Chemistry Master Doc PDF

Content IQ1 - Static and Dynamic Equilibrium Inquiry question: What happens when chemical reactions do not go through to completion? Students: conduct practical investigations to analyse the reversibility of chemical reactions, for example: – cobalt(II) chloride hydrated and dehydrated – iron(III)...

Content IQ1 - Static and Dynamic Equilibrium Inquiry question: What happens when chemical reactions do not go through to completion? Students: conduct practical investigations to analyse the reversibility of chemical reactions, for example: – cobalt(II) chloride hydrated and dehydrated – iron(III) nitrate and potassium thiocyanate – burning magnesium – burning steel wool model static and dynamic equilibrium and analyse the differences between open and closed systems analyse examples of non-equilibrium systems in terms of the effect of entropy and enthalpy, for example: – combustion reactions – photosynthesis investigate the relationship between collision theory and reaction rate in order to analyse chemical equilibrium reactions (ACSCH070, ACSCH094) IQ2 - Factors that Affect Equilibrium Inquiry question: What factors affect equilibrium and how? Students: investigate the effects of temperature, concentration, volume and/or pressure on a system at equilibrium and explain how Le Chatelier’s principle can be used to predict such effects, for example: – heating cobalt(II) chloride hydrate – interaction between nitrogen dioxide and dinitrogen tetroxide – iron(III) thiocyanate and varying concentration of ions explain the overall observations about equilibrium in terms of the collision theory examine how activation energy and heat of reaction affect the position of equilibrium IQ3 - Calculating the Equilibrium Constant (Keq) Inquiry question: How can the position of equilibrium be described and what does the equilibrium constant represent? Students: deduce the equilibrium expression (in terms of Keq) for homogeneous reactions occurring in solution perform calculations to find the value of Keq and concentrations of substances within an equilibrium system, and use these values to make predictions on the direction in which a reaction may proceed qualitatively analyse the effect of temperature on the value of Keq conduct an investigation to determine Keq of a chemical equilibrium system, for example: – Keq of the iron(III) thiocyanate equilibrium explore the use of Keq for different types of chemical reactions, including but not limited to: – dissociation of ionic solutions – dissociation of acids and bases IQ4 - Solution Equilibria Inquiry question: How does solubility relate to chemical equilibrium? Students: describe and analyse the processes involved in the dissolution of ionic compounds in water investigate the use of solubility equilibria by Aboriginal and Torres Strait Islander Peoples when removing toxicity from foods, for example: – toxins in cycad fruit conduct an investigation to determine solubility rules, and predict and analyse the composition of substances when two ionic solutions are mixed, for example: – potassium chloride and silver nitrate – potassium iodide and lead nitrate – sodium sulfate and barium nitrate derive equilibrium expressions for saturated solutions in terms of Ksp and calculate the solubility of an ionic substance from its Ksp value predict the formation of a precipitate given the standard reference values for Ksp IQ1 - Static and Dynamic Equilibrium IQ1 Dot Point 1 conduct practical investigations to analyse the reversibility of chemical reactions, for example: – cobalt(II) chloride hydrated and dehydrated What are – iron(III) nitrate and potassium thiocyanate reversible – burning magnesium reactions? – burning steel wool Thermodyna Reversible Reactions mic Reversible reactions can occur in both the forward and reverse directions, whereby properties of products can react to reform reactants reverse Reverse reaction has opposite thermodynamic properties compared to the forward reactions? reaction ○ i.e. if forward is exothermic, reverse is endothermic ○ i.e. if the forward is spontaneous, the reverse is non-spontaneous Cobalt (II) Chloride Hydration/Dehydration ➔ Dehydrating cobalt(II) chloride hexahydrate forms the intermediate cobalt(II) chloride Explain the dihydrate, then the anhydrous cobalt (II) chloride cobalt (II) ➔ Dissolving anhydrous cobalt(II) chloride in water produces a pink solution of cobalt(II) chloride chloride hexahydrate hydration and dehydration? STEP 1: 𝐶𝑜𝐶𝑙2 · 6𝐻2𝑂(𝑠)⇌ 𝐶𝑜𝐶𝑙2 · 2𝐻2𝑂(𝑠) + 4𝐻2𝑂(𝑙) Type of STEP 2: 𝐶𝑜𝐶𝑙2 · 2𝐻2𝑂(𝑠)⇌ 𝐶𝑜𝐶𝑙2(𝑠) + 2𝐻2𝑂(𝑙) reaction? Cobalt (II) chloride hexahydrate - dark pink Colours for Cobalt (II) chloride dihydrate - purple reactants/pro Anhydrous (containing no water) cobalt (II) chloride - sky blue ducts of cobalt (II) THE REACTION IS REVERSIBLE chloride? THE FORWARD AND REVERSE REACTIONS DO NOT OCCUR AT THE SAME TIME Burning Magnesium and Steel Wool Colours for magnesium 2𝑀𝑔(𝑠) + 𝑂2(𝑔) → 2𝑀𝑔𝑂(𝑠) oxide and iron oxide in ➔ Magnesium oxide, a white solid, is formed burning Mg ➔ A bright light is emitted and steel? 4𝐹𝑒(𝑠) + 3𝑂2(𝑔) → 2𝐹𝑒2𝑂3(𝑠) What is the ion charge for ➔ Iron (III) oxide, a reddish-brown solid, is formed iron in the reaction (and When either solids are placed in an ice bath, which provides conditions for the reverse reaction is it to occur, no changes happen → THE REACTION IS IRREVERSIBLE reversible?)? Systems Explain the 3 Open systems: a system interacts with the surroundings by allowing the exchange of different matter and energy types of Closed systems: a system where only energy is exchanged with the surroundings systems? Isolated systems: a system that doesn’t allow the exchange of matter or energy BOTH STATIC AND DYNAMIC EQUILIBRIUM ARE ONLY ACHIEVABLE IN CLOSED SYSTEMS Define static equilibrium? Static Equilibrium What is Occurs when the rates of forward and reverse reaction are equal and zero happening macro vs Cases (3) microscopical Irreversible reaction at completion ly? ○ Initially, the rate of forward reaction starts high. It reduces over time as the concentration of reactants reduces What are the ○ The reverse reaction doesn’t occur, so it has a rate of zero 3 cases of ○ Eventually, the rate of forward reaction reaches zero (static eq achieved) static + − 𝑁𝑎𝐶𝑙(𝑠) ⇌ 𝑁𝑎(𝑎𝑞) + 𝐶𝑙(𝑎𝑞) equilibrium?  Irreversible reaction before initiation ○ If insufficient energy is inputted, the forward and reverse reactions remain at zero ○ The combustion of a fuel without an initial spark 25 𝐶8𝐻18 (𝑙) + 2 𝑂2 (𝑔) → 8𝐶𝑂2 (𝑔) + 9𝐻2𝑂(𝑙) Reversible reaction with insurmountable activation energy ○ The diamond-graphite equilibrium: Define 𝐶(𝑠, 𝑑𝑖𝑎𝑚𝑜𝑛𝑑) ⇌ 𝐶(𝑠, 𝑔𝑟𝑎𝑝ℎ𝑖𝑡𝑒) , ∆𝐻 < 0 dynamic equilibrium. Dynamic Equilibrium Occurs when the forward and reverse reaction are equal and non-zero such that the Describe concentrations of the products and reactants are constant what is happening Macroscopically → nothing is happening macroscopica Microscopically → reactants are forming products and products are forming reactants at the lly vs same, non-zero rate, the reactant and product concentrations remain the constant microscopical ly? Just accept they're the same in school tho (one is standard state)  IQ1 Dot Point 2 model static and dynamic equilibrium and analyse the differences between open and closed systems Modelling Dynamic Equilibrium Use counters/use the straws experiment (see in methods) Advantages ** Advantages vs This demonstrates that the rate of forward reaction is proportional to the amount of disadvantage reactants, and the rate of reverse reaction is proportional to the amount of products s of using straws Pipettes have different volumes - models cases where the stoichiometric ratio is not 1:1 experiment to model Dynamic equilibrium is reached → when the volumes of water in cylinder A and B are dynamic constant, the rate at which the pipette transfers water is the same in both directions, equilibrium? representative of … The equilibrium can be re-established if it is disturbed The equilibrium constant, modelled by the ratio of volumes, is the same in the face of any disturbances made to the vessel Disadvantages This model does not deal with concentrations; it deals with volumes, meaning certain properties such as the intensity of a solution being emblematic of its concentration are lost Water can be spilled - water loss This system only models one reactant and one product Can’t model the effects of temperature and pressure Does not show the chemical changes when reactants become products, and vice versa IQ1 Dot Point 3 analyse examples of non-equilibrium systems in terms of the effect of entropy and enthalpy, for example: – combustion reactions – photosynthesis Definition of Enthalpy enthalpy? The internal energy of a substance or group of substances (𝐽 𝑚𝑜𝑙 −1 −1 𝑂𝑅 𝑘𝐽 𝑚𝑜𝑙 ) Formula for enthalpy? ∆𝐻 = 𝐻𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 − 𝐻𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠 OR ∆𝐻 = Σ𝐻 − Σ𝐻𝑏𝑜𝑛𝑑𝑠 𝑓𝑜𝑟𝑚𝑒𝑑 𝑏𝑜𝑛𝑑𝑠 𝑏𝑟𝑜𝑘𝑒𝑛 Rules What is ➔ Absolute enthalpy cannot be measured; only the change in enthalpy can be measured standard ➔ The standard enthalpy of formation is the change in enthalpy associated with the enthalpy of formation of 1 mol of a substance in its standard state from its constituent elements in formation? standard state ➔ The standard formation of an element is defined to be 0𝑘𝐽/𝑚𝑜𝑙 Rules for ➔ ∆𝐻 > 0 - reverse enthalpy drive, endothermic enthalpy? ➔ ∆𝐻 < 0 - forward enthalpy drive, exothermic Entropy The number of possible microscopic arrangements of particles in a system, referred to as Definition of the measure of disorder entropy? ** “Positional disorder” → actually refers to the energy configurations/arrangements The standard entropy values (So) represent the increase in entropy that occurs when a Formula for substance is heated from 0 K to 298 K at 100 kPa pressure. (basically entropy AT 298K) entropy? −1 −1 −1 −1 A measure of the state of disorder in a chemical system ((𝐽 𝑚𝑜𝑙 𝐾 𝑂𝑅 𝑘𝐽 𝑚𝑜𝑙 𝐾 ) Rules for entropy? ** 𝑜 𝑜 𝑜 ∆𝑆𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛 = Σ𝑆𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 − Σ𝑆𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠 Rules ➔ Absolute entropy can be measured ➔ Absolute entropy is always positive (theoretically 0 for a perfect crystal lattice at 0K) ➔ ∆𝑆 > 0 - forward entropy drive ➔ ∆𝑆 < 0 - reverse entropy drive Laws of Thermodynamics The Zeroth Law of Thermodynamics: if two systems are in thermal equilibrium with a third system, then all the systems are in thermal equilibrium with each other What are the 4 laws of The First Law of Thermodynamics: energy movement into or out of a system is in thermodyna accordance with the law of conservation of energy mics? *** The Second Law of Thermodynamics: the entropy of an isolated system not at equilibrium will increase over time, approaching a maximum value at equilibrium  ∆𝑆𝑢𝑛𝑖𝑣𝑒𝑟𝑠𝑒 = ∆𝑆𝑠𝑦𝑠𝑡𝑒𝑚 + ∆𝑆𝑠𝑢𝑟𝑟𝑜𝑢𝑛𝑑𝑖𝑛𝑔𝑠 > 0 The Third Law of Thermodynamics: the entropy of a system approaches a minimum as temperature approaches zero What is the definition of combustion Combustion vs The burning of a substance in oxygen, producing energy photosynthesi It is an exothermic process that goes to completion (∆𝐻 < 0) s? ** Typically has a forward entropy drive Photosynthesis A reaction whereby carbon dioxide and water react with light energy to form glucose and energy in the form of ATP; occurs in plants It is an endothermic, and thus has a positive enthalpy change Reduces the entropy of the system since it forms solid glucose molecules (∆𝑆 < 0) Relationship 𝑜 𝑜 between ∆𝐺 Relationship between ∆𝐺 and Reversibility and 𝑜 A chemical reaction with ∆𝐺 > 0 for all temperatures is non-spontaneous, and is likely to Reversibility? be an irreversible chemical reaction ○ e.g. photosynthesis 𝑜 A chemical reaction with ∆𝐺 < 0 for all temperatures is spontaneous, and likely to be an irreversible chemical reaction ○ e.g. combustion Explain if Reversible reactions tend to have competing entropy and enthalpy drives: 𝑜 𝑜 photosynthesi ○ ∆𝐻 > 0 (reverse enthalpy) and ∆𝑆 > 0 (forward entropy) s and 𝑜 𝑜 ○ ∆𝐻 < 0 (forward enthalpy) and ∆𝑆 < 0 (reverse entropy) respiration are a fwd and There are exceptions to these rules reverse reaction pair. Note: PHOTOSYNTHESIS AND RESPIRATION ARE NOT A FORWARD AND REVERSE REACTION PAIR → the conditions of either reaction are vastly different What is an Exergonic Reaction exergonic vs A reaction where ∆𝐺 < 0, meaning that it is spontaneous and releases free energy endergonic? ** Endergonic Reaction A reaction where ∆𝐺 > 0, meaning that it is non-spontaneous and requires free energy  IQ1 Dot Point 4 investigate the relationship between collision theory and reaction rate in order to analyse chemical equilibrium reactions (ACSCH070, ACSCH094) Collision Theory Collision States that chemical reactions occur when particles with sufficient energy collide at the theory correct orientation in a successful collision to form stable bonds definition? Explanation for Reversible Reactions (for concentration/progress of reaction) ➔ Initially, there is a high concentration of reactants, causing a high frequency of collisions between reactant particles, by collision theory, and thus meaning that the rate of the Collision forward reaction is high theory ➔ Overtime, the concentration of reactants decreases as they are converted to products, explanation decreasing the frequency of reactant particle collisions and causing the rate of the for reversible forward reaction to reduce reactions? ** 𝑅𝑎𝑡𝑒 𝑜𝑓 𝑓𝑜𝑟𝑤𝑎𝑟𝑑 𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛 α 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠 ➔ Conversely, due to the increased concentration of products, the frequency of collisions between products will rise, increasing the rate of the reverse reaction 𝑅𝑎𝑡𝑒 𝑜𝑓 𝑓𝑜𝑟𝑤𝑎𝑟𝑑 𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛 α 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 ➔ This continues until the forward and reverse reactions equalise at the same, non-zero rate at dynamic equilibrium, whereby the concentrations of the reactants and products are constant EXAMPLE 2𝐴(𝑔) ⇌ 𝐵(𝑔), ∆𝐻 < 0  The ratio of the rate of reaction increases are not relevant to the stoichiometric ratio (above diagram 1 and 2 wrong) IQ2 - Factors that Affect Equilibrium IQ2 Dot Point 1 investigate the effects of temperature, concentration, volume and/or pressure on a system at equilibrium and explain how Le Chatelier’s principle can be used to predict such effects, for example: – heating cobalt(II) chloride hydrate – interaction between nitrogen dioxide and dinitrogen tetroxide – iron(III) thiocyanate and varying concentration of ions What is the Le Chatelier’s Principle (LCP) definition of If a system at dynamic equilibrium is disturbed, then the system will shift to minimise the Le Chatelier’s disturbance until a new equilibrium is reached Principle? ** ➔ If the system shifts to the RIGHT, then the rate of forward reaction begins to exceed the rate of reverse reaction ➔ If the system shifts to the LEFT, then the rate of reverse reaction begins to exceed the rate of forward reaction What are the The factors that affect the point of Equilibrium factors that Concentration affect the Temperature point of Pressure/volume equilibrium? Concentration Concentration increase by By LCP LCP vs ➔ If the concentration of a substance in equilibrium is changed, the system will shift to collision favour the reaction that counteracts the initial change theory? (use ➔ In general, if a pure solid or liquid is added or removed from a system, there will be no reactants) effect on the equilibrium ◆ This is because solids and liquids are virtually incompressible, and their Does concentrations are essentially constant removing/ad ding a solid or ➔ If a solvent is added or removed from a system, changes to the equilibrium will be liquid affect observed the + − ◆ 𝐴𝑔𝐶𝑙(𝑠) ⇌ 𝐴𝑔(𝑎𝑞) + 𝐶𝑙(𝑎𝑞) equilibrium? ◆ Addition of liquid water will cause a reduction in the concentrations of + − 𝐴𝑔(𝑎𝑞) 𝑎𝑛𝑑 𝐶𝑙(𝑎𝑞) , since c=n/V ◆ By LCP, the system will shift to increase the concentration of the ions, and hence the forward reaction is favoured and the system shifts to the side of the products (to the right) − − + e.g. 𝐶𝑙2 (𝑔) + 𝐻2𝑂(𝑙) ⇌ 𝐶𝑙(𝑎𝑞) + 𝐶𝑙𝑂(𝑎𝑞) + 2𝐻(𝑎𝑞) If KCl is added to the system: − [𝐶𝑙 ] increases − System shifts to the left by favouring the reverse reaction to remove 𝐶𝑙 (by LCP) − − This lowers [𝐶𝑙 ], thereby minimising the overall change in [𝐶𝑙 ] By Collision Theory The concentration of the reactants is increased Increase in the frequency of collisions, by collision theory Increase in the number of successful collisions Increase in the rate of the forward reaction, by collision theory System will favour the forward reaction and shift right Temperature Temperature By LCP increase by The system will shift as to minimise the effect of the temperature change LCP vs by 𝑁2 (𝑔) + 3𝐻2(𝑔) ⇌ 2𝑁𝐻3(𝑔), ∆𝐻 < 0 collision theory? (use If the temperature is increased: example on ○ System shifts to favour the reverse, endothermic reaction that removes heat i.e. the right) ** shifts to the LEFT ○ Thus, the temperature is lowered, minimising the initial change ○ NOTE: [𝑁2] and [𝐻2] increases, while [𝑁𝐻3] decreases If the temperature is decreased: ○ System shifts to favour the forward, exothermic reaction to produce heat i.e. shifts to the right ○ NOTE: [𝑁2] and [𝐻2] decreases, while [𝑁𝐻3] increases NOTE: rate of reaction change is instantaneous for temperature What does an increase in temperature look like on a rate of reaction-time graph? ** By Collision Theory Increase in the temperature will increase the proportion of particles with enough energy to overcome the activation energy barrier → this increases the success rate ○ Increasing the temperature has a greater effect on the reaction rate when the activation energy is higher → this is because a greater relative proportion of molecules will now have enough energy to overcome the activation energy barrier  2 Additionally, since 𝐾 α 𝑣 , the velocity will increase, resulting in an increase in the frequency of collisions OVERALL, increase in the number of successful collisions → increase in ROR ALWAYS DRAW MAXWELL BOLTZMANN FOR TEMP E.g. IF a reaction has forward endo, reverse exo However, since the forward endothermic reaction has a higher activation energy, the rate of forward reaction is increased to a greater extent than the rate of reverse reaction → formation of more product molecules THUS the endo reaction is favoured Explanation: An endothermic reaction will have a greater activation energy Thus, any increase to the number of particles with energy > activation energy by temperature, will be greater %-wise compared with exothermic reactions As a result, the increase in reaction rate will be more significant for an endothermic reaction as there is a greater % increase in particles with energy > activation energy Pressure increase by LCP vs by collision theory**? Pressure AND/OR Volume Partial pressure: a gas’ hypothetical pressure if it were the only gas occupying the volume of the mixture Total pressure of an ideal gas mixture: the sum of the partial pressures of each of the component gases By LCP Partial pressure example 2𝑁𝑂2(𝑔) + 𝐻2𝑂(𝑙) ⇌ 𝐻𝑁𝑂3 (𝑎𝑞) + 𝐻𝑁𝑂2 (𝑎𝑞) If 𝑁𝑂2 (𝑎𝑞)is pumped in: Since the number of moles of NO2 per unit volume increases, the partial pressure of 𝑁𝑂2 increases as per 𝑃 α 𝑛/𝑉 (rearrange ideal gas law) The system shifts to favour the forward reaction, which consumes 𝑁𝑂2 , and so lowers the number of moles of 𝑁𝑂2 per unit volume This decrease the partial pressure of 𝑁𝑂2 , counteracting the initial change. The system has shifted to the right Total pressure example 𝑁2 (𝑔) + 3𝐻2(𝑔) ⇌ 2𝑁𝐻3(𝑔), ∆𝐻 < 0 If the total pressure of the system increased ○ The number of moles of gas per unit volume increases, since the volume decreases for the same number of moles Increase in ○ Since the molar gas ratio for reactants and products is 4:2, the system will favour pressure graphical the forward reaction which decreases the number of moles present in the system illustration? and thus counteracts the initial change by LCP ○ Therefore, the system will shift to the right 1. Reaction with gases and other states - refer to partial pressure only 2. Reaction with only gases - refer to total pressure (talk about molar ratio as seen above) By Collision Theory 𝑁2 (𝑔) + 3𝐻2(𝑔) ⇌ 2𝑁𝐻3(𝑔) Decrease in volume, increase in the total pressure Both reactants and products are closer together, increasing the collision frequency and thus the rate of reaction in both the forward and reverse direction However, since there are more moles of reactants, there are more frequent collisions between reactant particles, meaning there is greater increase in the no. of successful collisions for reactants The rate of forward reaction increases to a greater extent than the rate of reverse reaction, until a point where enough product molecules are formed that both the forward and reverse reaction rates are equal at dynamic equilibrium. Since more product molecules were formed, the equilibrium shifted to the right Addition of an 2𝐴(𝑔) ⇌ 𝐵(𝑔), ∆𝐻 < 0 inert gas increase by LCP and collision theory?**impo rtant Catalyst Addition of Inert Gas effect By LCP explanation? 𝑁2 (𝑔) + 3𝐻2(𝑔) ⇌ 2𝑁𝐻3(𝑔), ∆𝐻 < 0 Addition of an inert gas will increase the total pressure of the system However, the partial pressure of each reactant and product is unchanged, since the number of moles of each gas and the volume of the CONTAINER is unchanged Therefore, there will be no effect on the equilibrium position. However, the inert gas will decrease the rate of reaction and increase the time of reaction.  By Collision Theory Will not change the partial pressures Any collisions between inert gas molecules and the molecules partaking in the chemical reaction will be unsuccessful However, these additional unsuccessful collisions will obstruct potentially successful collisions, and reduce both the forward and reverse rates of reaction Hence, the time taken to reach equilibrium will be longer Catalysis By LCP (A non-reagent that increases the rate of reaction by providing an alternate pathway with a lower activation energy, and is not consumed at the end of the reaction) Catalysts have no effect on the equilibrium position What is the INSTEAD, they hasten the attainment of equilibrium. rule of ○ The reactants will be depleted more rapidly nullification? ○ The products will be produced more rapidly What are the colours of dinitrogen tetroxide and nitrogen dioxide? ** What is a metal The rate of forward and reverse reaction rate will increase complex?** Example? Nullification How does the Any disturbance to the system will be counteracted by a shift in the system, but it will example never be completely nullified or overcompensated for work? → this includes any changes in concentration induced by pressure changes (if pressure decreases, the system will shift to increase the pressure of the system; the concentration of the Effect of reactant that is favoured will never exceed its initial CONCENTRATION) → use quantitative Keq changing the calculation/graph to confirm. temperature? ** Need to know the colours of dinitrogen tetroxide and nitrogen dioxide NO2 - brown N2O4 - colourless  A metal complex has a metal ion at its centre with a number of other molecules or ions surrounding it → cobalt hexahydrate is a metal complex − This metal complex interacts with the dissociated 𝐶𝑙(𝑎𝑞) via the following: 2+ − 2− 𝐶𝑜(𝐻2𝑂)6 (𝑎𝑞) + 4𝐶𝑙(𝑎𝑞) ⇌ 𝐶𝑜𝐶𝑙4 (𝑎𝑞) + 6𝐻2𝑂(𝑙), ∆𝐻 > 0 Cl and H2O are colourless The forward reaction is endothermic: If the reaction mixture is heated, the equilibrium will shift to favour the forward endothermic reaction (RIGHT), resulting in the solution becoming more blue If the reaction mixture is cooled, the equilibrium will shift to favour the reverse exothermic reaction (LEFT), resulting in the solution becoming more pink IQ2 Dot Point 3 examine how activation energy and heat of reaction affect the position of equilibrium Catalyst What are Catalysts are non-reagents that increase the rate of reaction by providing an alternate catalysts? pathway with a lower activation energy. The rates of the forward and reverse reactions will be simultaneously increased, so this Explain its will not change the relative concentrations of reactants and products at equilibrium effect on the Hence, changes to the activation energy due to the presence or absence of a catalyst will equilibrium. NOT affect the value of 𝐾𝑒𝑞 However, a catalyst will hasten the attainment of equilibrium  IQ3 - Calculating the Equilibrium Constant IQ3 Dot Point 1, IQ3 Dot Point 2, IQ3 Dot Point 3 deduce the equilibrium expression (in terms of Keq) for homogeneous reactions occurring in solution perform calculations to find the value of Keq and concentrations of substances within an equilibrium system, and use these values to make predictions on the direction in which a reaction may proceed qualitatively analyse the effect of temperature on the value of Keq Equilibrium Constant What is the For a reaction at equilibrium, there is a quantitative relationship between the equilibrium concentrations of reactants and products referred to as the equilibrium constant 𝐾𝑒𝑞 constant? 𝑐 𝑑 [𝐶} ·[𝐷] Formula? 𝑎𝐴 + 𝑏𝐵 ⇌ 𝑐𝐶 + 𝑑𝐷 → 𝐾𝑒𝑞 = 𝑎 𝑏 [𝐴] ·[𝐵]  A,B,C and D must be aqueous or gaseous, since the concentration of solids/liquids is constant Explain what If 𝐾𝑒𝑞 is large, the equilibrium position lies significantly to the side of the products (to the right) can be If 𝐾𝑒𝑞 has a middling value (0.1 to 10), there are comparable amounts of both reactants and inferred if the K is large, products middling or If 𝐾𝑒𝑞 is small, the equilibrium position lies significantly to the side of the reactants (to the left) small. What are the three different strategies for solving questions involving K? Explain the 3 manipulations of the equilibrium constant.  The Reaction Quotient The quantitative relationship between the concentrations of the reactants and products for a reaction not yet at equilibrium: What is the reaction 𝑐 𝑑 quotient? [𝐶} ·[𝐷] 𝑄 = 𝑎 𝑏 [𝐴] ·[𝐵] What does the relative If 𝑄 < 𝐾 (inferring that [products] < [reactants] since products are on the numerator), the magnitude of system will proceed to the right, to increase the concentration of the products Q to K tell us? If 𝑄 > 𝐾, the system will proceed to the left, to increase the concentration of the reactants If 𝑄 = 𝐾, the system is at equilibrium What is the factor that Note: a “new” equilibrium is established when rates changed AND new concentration changes the established equilibrium The pressure, volume or concentration will establish a new equilibrium, but the old K constant? value will satisfy Temperature is the only factor that can change the K value Temperature and Equilibrium Constant K value changes based on whether the forward reaction in the equilibrium is exothermic or endothermic: An increase in temperature would cause an exothermic reaction to shift left by Le Chatelier’s Principle, thus reducing the concentration of products, hence reducing 𝐾𝑒𝑞. The converse will happen with an increase in 𝐾𝑒𝑞 in an endothermic reaction. A decrease in temperature would cause an exothermic reaction to shift right by Le Chatelier’s Principle, thus increasing the concentration of products, hence increasing 𝐾𝑒𝑞. The converse will happen with a decrease in 𝐾𝑒𝑞 in an endothermic reaction. IQ3 Dot Point 4 conduct an investigation to determine Keq of a chemical equilibrium system, for example: – Keq of the iron(III) thiocyanate equilibrium 3+ − 2+ 𝐹𝑒(𝑎𝑞) + 𝑆𝐶𝑁 ⇌ (𝐹𝑒𝑆𝐶𝑁)(𝑎𝑞), ∆𝐻 < 0 Iron thiocyanate 3+ reaction and 𝐹𝑒(𝑎𝑞) is pale yellow → apparently pale-orange too? colours − please. 𝑆𝐶𝑁 is colourless  2+ (𝐹𝑒𝑆𝐶𝑁)(𝑎𝑞) is blood-red What is Colorimetry: a method of analysis which relates the absorption of light of a specific wavelength colourimetry? by a coloured solution to a quantitative measure of the concentration of the solute ** 𝐴𝑏𝑠𝑜𝑟𝑏𝑎𝑛𝑐𝑒 α 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 Creating the Calibration Curve 2+ To create standard solutions of (𝐹𝑒𝑆𝐶𝑁)(𝑎𝑞), we need to react iron (III) nitrate and potassium thiocyanate 3+ − 2+ 𝐹𝑒(𝑎𝑞) + 𝑆𝐶𝑁 ⇌ (𝐹𝑒𝑆𝐶𝑁)(𝑎𝑞) How do you create Since the reaction is reversible however, we need to ensure that the position of standard − solutions? equilibrium lies heavily to the right, such that the amount of 𝑆𝐶𝑁 which is not converted 2+ to (𝐹𝑒𝑆𝐶𝑁)(𝑎𝑞) is negligible We can do this by using a concentration of iron (III) nitrate at least 100 times greater than that of potassium thiocyanate. Since the molar ratio of thiocyanate ion to the iron (III) thiocyanate ion is 1:1, the concentration of iron thiocyanate produced will be virtually equal to the concentration of thiocyanate ion consumed 2+ Alternatively, standard solutions of (𝐹𝑒𝑆𝐶𝑁)(𝑎𝑞) can also be created by using solutions − 3+ where [𝑆𝐶𝑁 ]>> [𝐹𝑒 ] (better as SCN is colourless, no inference with colorimetry) LIMITING REAGENTS ARE NOT RELEVANT IN THE CONTEXT OF EQUILIBRIUM IQ3 Dot Point 5 explore the use of Keq for different types of chemical reactions, including but not limited to: – dissociation of ionic solutions – dissociation of acids and bases  IQ4 - Solubility Equilibria IQ4 Dot Point 1 describe and analyse the processes involved in the dissolution of ionic compounds in water Rule for Like dissolves like solubility, as A solute will dissolve if the formation of intermolecular forces between the solute and in what solvent are more favourable than the existing intermolecular forces between the solute dissolves molecules and between the solvent molecules (explicitly state it with the actual what? molecule names) What ○ Solute-solute interactions are overcome interactions ○ Solvent-solvent interactions are overcome are ○ Ion-dipole focus are formed overcome/for med? e.g. When NaCl dissolves in water, the slightly positive hydrogens in the polar H2O molecule will − orient themselves towards the 𝐶𝑙 anions, while the slightly negative oxygens orient themselves + towards the 𝑁𝑎 cations Name 3 that Dissolve exothermically Dissolve endothermically dissolve exo vs CaCl2 KCl endothermica lly. ** Na2CO3 NaHCO3 NaOH NH4NO3 How does the entropy of a The entropy of the system usually increases during dissolution solid system The ionic lattice has a low entropy since the ions are fixed in position and exhibit very little increase movement during Following dissolution, the hydrated ions are free to move about in solution, giving the dissolution? system a high entropy How does dissolution occur? - Ionic bonds are extremely strong. So how do the water molecules with their weak intermolecular forces break ionic lattices? Multiple water molecules surround the “weakest” points on the ionic lattice, namely the edges or corners, and are capable of accumulating sufficiently strong attractive ion-dipole forces to exceed those solute-solute interactions (ionic bonds), and break off ions from these sites Dissolution as an Equilibrium Dissolution can either be static or dynamic, depending on whether it is unsaturated or saturated  2+ − 𝐶𝑎𝐶𝑙2(𝑠) → 𝐶𝑎(𝑎𝑞) + 2𝐶𝑙(𝑎𝑞) If only a small sample of CaCl2(s) is added to water, it will completely dissolve and there will be no CaCl2(s) left over. This is known as an unsaturated solution. ○ This is because static equilibrium and not dynamic equilibrium is reached, since the forward reaction is heavily favoured with small quantities of solute. 2+ − 𝐶𝑎𝐶𝑙2(𝑠) ⇌ 𝐶𝑎(𝑎𝑞) + 2𝐶𝑙(𝑎𝑞) A saturated solution is formed when sufficient CaCl2(s) is dissolved in water such that a dynamic equilibrium is just established ○ The rates of the forward and reverse reaction gradually become equal, and dissociation is occurring at the same rate as precipitation ○ When solute is added to a saturated solution, the total mass of dissolved solute will NOT increase. However, a dynamic equilibrium is still formed such that the ions are in constant motion (since the forward reaction of dissociation is equal to the reverse reaction of precipitation) > 10g/L → soluble 1-10g/L → sparingly soluble 0 4. Define LCP 5. The crushed kernel is placed into a stream of running water to leach out the cycasin, causing the depletion of aqueous cycasin. The system will shift to the right by favouring the forward, endothermic reaction to increase the concentration of aqueous cycasin and minimise the change by LCP. 6. By placing the kernel in boiling water to increase the temperature, the system will favour  the forward, endothermic reaction to counteract the increase in temperature, thus increasing the yield of aqueous cycasin and speeding up the process of leaching. 7. Repeated steps of this leaching and boiling rids of most of the solid cycasin toxin. Solubility Rules ** Structure for LCP Increase in temperature Equilibrium shifts to the left  1. Explain the disturbance and its effect on the system (for a pressure or concentration question, also state the stoichiometric coefficients) 2. Explain how LCP will negate the disturbance, and its effect on the concentration of species in the reaction 3. State which direction the reaction will favour 4. State that this is in accordance with LCP 5. State that this will occur until equilibrium is restored assuming a constant temperature The pressure increases. As the gas molar ratio is 2:1, the system will shift right by favouring the forward reaction to decrease the total concentration of all gaseous species, decrease the total pressure and thus minimise the disturbance until a new equilibrium is reached by Le Chatelier’s Principle.