Chemistry Notes PDF

5.2 Chem Notes: Specific Heat Capacity: the quantity of thermal energy required to raise the temperature of 1 g of substance by 1°C. Certain substances require a lot more thermal energy to raise their temperature due to each one having different heat capacities. High heat capacities also req...

5.2 Chem Notes: Specific Heat Capacity: the quantity of thermal energy required to raise the temperature of 1 g of substance by 1°C. Certain substances require a lot more thermal energy to raise their temperature due to each one having different heat capacities. High heat capacities also require more time to cool down Calorimetry is the experimental process of measuring the thermal energy change in a chemical or physical change The total amount of thermal energy in a substance is sometimes called enthalpy. The energy change that occurs in the system during a reaction is called the enthalpy change. If pressure is constant, then SH system For chemical reaction temp change:1951 products Itreactants The molar enthalpy change of reaction for a substance is the energy that occurs when one mole of that substance undergoes, a physical chemical or nuclear change 5.3 Textbook Notes: The quantity of energy required to break a chemical bond is its bond dissociation energy (always positive values) For example, for C-H, it takes 413 kJ of energy to break one mole of the C-H bond into one mole of C atoms and one mole of H atoms The more bonds between atoms, for example, triple or double bonds, the more bond energy is required to break them To figure out the bond energy change, using bond energy values, the bonds in the reactants must first break. Energy must be added for bonds to break. The energy change or enthalpy of the reaction is the difference between these two sums. 5.4 Textbook Notes: The change in enthalpy in a chemical process is independent of the path taken. This means that in going from an initial set of reactants to a final set of products, the change in enthalpy is the same regardless of whether the conversion happens in one step or in a series of steps. The change in enthalpy would always be the same, no matter how many steps it took to obtain the desired product. Hess’ Law: the change for the conversion of reactants to products is the same whether the conversion occurs in one step or several steps. There are two rules to follow for Hess’ Law: 1. If you reverse a chemical reaction, you must also reverse the sign of H. 2. The magnitude of H is directly proportional to the number of moles of reactants in products in a reaction if the coefficient in a balanced equation or multiplied by a factor, the value of H is multiplied by the same factor. The law of conservation of energy states that energy cannot be created or destroyed, however, it can be converted from one form to another, and transferred between a system and its surroundings. Hess’s law supports this theory as the overall energy change of a chemical process equals the sum of the energy changes of the individual steps. This indicates that the overall change in energy of a process is constant—energy cannot be created or destroyed but transferred from step to step. The characteristic of enthalpy change that is the basis of Hess’s Law is the flow of thermal energy. If the direction of the reaction is reversed, the direction of the thermal energy flow must also be reversed. That is, the sign of the ΔH value, which indicates the flow of thermal energy, is reversed. 5.5 Textbook Notes: The standard enthalpy of formation of a compound is the change in enthalpy that occurs when 1 mol of a compound is formed from its elements, with all substances in their standard states. Standard state: a substance isn’t a standard state when it is in its most stable form at standard  pressure and room temperature (SATP) - 25C, 100KPA Remember that bromine and mercury are at a state at temperature while iodine is a solid. Meanwhile, the standard state for a substance in solution is at a concentration of one 1mol/L. An element in standard state by itself is assigned a standard enthalpy of formation of zero since nothing is being formed and since the element is in its most fundamental form at standard conditions. 6.1 Notes: Chemical kinetics is the branch of chemistry concerned with the rates of chemical reactions. A rate is a change in a measurable quantity over time. The reaction rate of a chemical reaction is the change in concentration of a reactant or product per unit time You can measure the rate of reaction for gas production, colour change using a spectrophotometer, even colour intensity, even pH, gas volume, etc. The change in concentration of a reactant or product over a specified time period is the average rate of reaction of a reactant or product. In the formula, the symbol, delta, indicates a change in a given quantity, and chemical symbols placed inside the square brackets indicate the entity’s concentration in moles per litre A negative sign indicates the consumption of a reactant while a positive sign indicates the production of a product. The numerical value of the reaction rate can therefore always be a positive number. 6.2 Notes: The chemical nature of a pure substance gives it its chemical properties. A chemical property relates to the behaviour of a pure substance when it undergoes the chemical change or reaction. The tendency of a substance to undergo chemical reactions, such as combustion or oxidation reactions, is an example of a chemical property Sometimes the rate of a reaction is due to the chemical nature of the reactants such as the reactant oxidizing The rate of many chemical reactions increases at higher concentrations of reactants. When reactants are in different states of matter (ex: solid and liquid), the greater the surface area of the solid being reacted, the faster the reaction rate In general, the rate of a chemical reaction increases with the temperature at which it is carried out A catalyst is a substance that changes the rate of a chemical reaction but remains unchanged during the reaction, so it can participate in the same reaction over and over again A homogeneous catalyst, such as many enzymes in aqueous solutions in cells, has the same phase as the reactants. A heterogeneous catalyst, such as the metal in a catalytic converter, has a different phase than the reactants. Biological catalysts control most biological reactions, and most are enzymes 6.3 Notes: Collision theory states that chemical reactions can occur only if reactant atoms, molecules, or ions collide. Furthermore, the reactant entities must collide at an orientation and with enough kinetic energy that any bonds in the reactants will break and new bonds will form, making the products The rate of a reaction depends on the frequency and the proportion of collision that convert reactants into products. An increase in the frequency of effective collisions leads to a higher reaction rate For a reaction to actually occur, the reactants must also have sufficient enough kinetic energy The minimum amount of energy are reactant entity must have for a collision to be effective is called the activation energy (the minimum energy that reactant molecules must possess for a reaction to be  successful) READ ALL OF PAGE 367 OVER AGAIN In a chemical reaction, the potential energy is the energy stored in the bonds within and among the entities of the reactants, and the kinetic energy is their movement The activated complex is an unstable arrangement of atoms containing partially formed and unformed bonds that represent the maximum potential energy point in the change. Also called the transition state or the peak of the reaction or graph. As temperature increases, the kinetic energy of the molecules also increases, which can cause more collisions and more collisions can increase the chances of effective collisions and increase the rate of reaction Only entities with kinetic energy equal to or greater than the activation energy can be involved in an effective collision. At a given temperature, only a certain fraction of the reactant entities will possess enough kinetic energy to equal or exceed the activation energy and some might not have enough kinetic energy. This is why temperature is the average kinetic energy of the whole reaction shaboingle. Reaction rates usually increase exponentially with temperature. Increases in temperature also increase the probability of effective collisions. Reactions where bonds must be broken first took before forming new products require much more energy than if simply ions were being combined together More complex molecules with complex bonds require more energy and are actually less reactive, making it harder to react and requiring more energy Increasing the concentration of reactants increases the probability of collisions between reactants, and hence a greater number of effective collisions is likely to occur Increasing the surface area is similar to increasing the concentration in that your increasing the probability of effective collisions by breaking up larger molecules or large crystal lattices of molecules into smaller ones with more surface area and more chances to react with the other liquid reactant A catalyst, instead of increasing the number of collisions or increasing the kinetic energy of the entities, can actually provide an alternate pathway for the reaction which has a lower activation energy (this still increases the reaction rate) 6.5 Notes: A chemical rate law is an equation that connects the rate of a reaction with the concentrations of its reactants at a given temperature and pressure (think of it as a function that allows for the calculation of reaction rate as a function of reactant concentration) Experimental evidence has shown that the rate of a reaction is proportional to the product of the initial concentrations of the reactants (equation) The rate constant, also known as k, is unique for each reaction and must be determined experimentally. K also varies with temperature so temperature must be kept constant. The reaction law equation is the relationship among the rate, the rate constant, the initial concentrations of reactants and the orders of reaction with respect to the reactants The order of reaction is the exponent used to describe the relationship between the initial concentration of a particular reactant and the rate of the reaction 6.6 Notes: an elementary step is a step that only involves one-, two- or three-entity collisions and that cannot be explained in terms of simpler reactions A reaction mechanism is the series of elementary steps by which the chemical reaction occurs. The rate-determining step is the step in a reaction mechanism that determines the rate of the overall reaction; it is the slowest step in a reaction mechanism A reaction intermediate is an entity that is neither a reactant nor a product, but is formed and consumed during the reaction sequence  Reaction steps that involve only 1 reactant entity include those in which a single entity collides with the size of the container and breaks apart into smaller entities Elementary steps involving three reactant molecules are very rare because it can be quite rare for three entities to simultaneously collide with each other than for just two entities to collide with each other The rate light equation cannot be derived from a balanced chemical equation, however it can be written directly from the balanced equations representing elementary steps Noticed that the rate law equation for an elementary step with one reactant molecule is always first order and the rate law equation for an elementary step with two reactant molecules is always second order To be plausible, a reaction mechanism must satisfy two requirements: firstly sum the elementary steps in the reaction mechanism must give the overall balanced equation for the reaction. Secondly, the reaction mechanism must agree with the experimentally determined rate law. The rate of the overall reaction is primarily controlled by the rate of this step, just as the slowest part of a journey to a concert might be the bus ride The slowest step in the elementary step steps is the red determining factor because that is the rate of the entire reaction throughout 7.1 Notes: any chemical reaction carried out in a close system will eventually reach chemical equilibrium. Chemical equilibrium is the state of a reaction in which all reactants and products have reached constant concentrations in a closed system All reactions in chapter 7 take place in a closed system All chemical equilibrium are dynamic equilibrium. A dynamic equilibrium is an equilibrium which the rates of four and reverse processes are equal. It is a balance between forward and reverse processes that are occurring simultaneously at equal rates. Under the conditions of a closed vessel at a high temperature, the chemical reaction begins immediately and progresses very quickly. The equilibrium position is the relative concentration of reactants and products in the system in a dynamic equilibrium Reversible reactions are chemical reactions that can proceed in both the forward and reverse directions. In a dynamic equilibrium the reaction rates in the forward and reverse directions of a reversible reaction are equal, and so a constant concentration of reactants in products will always be present. The system reaches equilibrium once the rate of the forward reaction becomes equal to the rate of the reverse reaction. Any equilibrium position can be reached starting from the forward reaction or from the reverse reaction Regardless of which substance was the reactant, and which was the product, the final concentrations of the gases at equilibrium are the same in a reverse or forward reaction. For a close chemical equilibrium system in constant environmental conditions, the same equilibrium concentrations or reach, regardless of the direction by which equilibrium was reached. You can predict the changes and concentration of reactants and products as a system approaches equilibrium from the coefficients of a balanced chemical equation. 7.2 Notes: The equilibrium constant is a constant numerical value that defines the equilibrium law forgiven system. The units are not included on giving the value of K. In a closed system under the same environment for a chemical reaction, even if the concentrations are changed, the equilibrium constant will still be the same every time. The value remains the same regardless of initial concentrations. However, the value of the equilibrium constant depends on the reaction temperature The equilibrium constant K can be used to determine the equilibrium position of a chemical reaction  system as being far right or far left. Even though the forward and reverse reactions in an equilibrium reaction are the same rates, the equilibrium constants of these two reactions are different, however they are mathematically connected, with one of them being the reciprocal of the other The ratio of the rate constants (little k) of the forward and reverse reactions is equal to the equilibrium constant, K A homogeneous equilibrium is where all reactants and products in the system are in the same state of matter. When the reactants and products in the chemical equilibrium system are present in more than one state, the system is a heterogeneous equilibrium The concentrations of pure solids or pure liquids cannot change If pure solids or pure liquids are involved in a chemical equilibrium system, their concentrations are not included in the equilibrium law equation for the reaction system In the equation for the equilibrium constant, you do not include pure liquids or pure solids because their concentrations cannot change. However, aqueous solutions and gases can have their concentrations changed for the same amount of volume, which is why they can be included in the equation Pure solids and liquids are not included in the equilibrium expression because their concentrations do not change during the reaction. The concentration of a pure solid or liquid is essentially its density, which remains constant regardless of the amount present. The mass amounts may change, but not the concentration, and the equilibrium constant is dependant on concentrations and temp only 7.4 Notes: Le Chatelier principle: when a chemical system equilibrium is disturbed by a change in a property, the system adjusts in a way that opposes the change. Basically a chemical system always tries to restore equilibrium whenever a change occurs to its original equilibrium. An equilibrium shift is a change in concentrations of reactants and products in order to restore an equilibrium state When additional reactants are added, the equilibrium concentration of the added reactant in the new equilibrium is usually higher than was its equilibrium concentration in the original equilibrium. Le Chatelier’s principle also predicts that removing some of the reactant in a chemical system at equilibrium will shift the equilibrium to the left towards the reactants to partially counteract the lower reactant concentration At the chemical level, the reason why adding reactants to an equilibrium system shifts it to the right is because there are more effective collisions happening due to their being more concentration. If instead, we add more product entities, then the number of successive collisions for the reverse reaction will increase, and the equilibrium will shift to the left. A system at equilibrium will also shift when it is disturbed by the addition or removal of energy (temperature - thermal energy) If an endothermic reaction is cooled, so the thermal energy is removed, we can consider that the quantity of one of the reactants has been decreased, therefore, we can predict that the equilibrium will shift to the left towards the reactants and energy will be released. If thermal energy is removed from an exothermic reaction where energy is a product, then the equilibrium will shift to the right toward the products, and energy will be released counteract to change A partial pressure is the pressure that a gas in a mixture of gases would exert if it alone occupied the whole volume or occupied by the mixture. It is basically the pressure exerted by one gas in a mixture, and is the same pressure as it would exert alone. It is possible to modify the amount of reactions and products using methods that do not change the equilibrium position. This can include adding a catalyst, adding an inert gas, or changing the state of the reactants. A catalyst lowers the activation energy of a reactant so the equilibrium point is the same however,  the reaction is simply just faster. An inert gas is a gas that is not reactive so it can be placed into a container with a set volume to increase the pressure which can increase the amount of product yield When a chemical system involves entities in more than one state of matter, equilibrium is affected only by the changes in concentration of entities that are in the same state of matter as the substances involved in the chemical reaction system. 7.5 Notes: The equilibrium law equation allows us to predict equilibrium shifts quantitively The reaction quotient is the ratio of of the product of the concentrations of the products to the product of the concentrations of the reactants. It doesn’t necessarily have to be equilibrium and can be at any point in the reaction. instantaneous concentrations are set of concentrations that correspond to a particular instant in time When the concentration of any reactant or product is zero, the chemical equilibrium system will shift in the direction that produces the missing substance 7.6 Notes: Solubility is the quantity of a solute that dissolves in a solvent under specific conditions such as the amount of sugar that can dissolve in water at 100°C The reason why a chemical reaction that forms a precipitate is a dynamic equilibrium is because: at the beginning, the molecule might split up into its individual ions however, as the reaction proceeds, those ions might collide with each other in the solution to form a precipitate solid again until a dynamic equilibrium is achieved. At this point, the rate at which ions in the solid dissolve, is equal to the rate at which the aqueous ions themselves precipitate. At equilibrium, the solution is saturated in that it contains the maximum quantity of solute at a given temperature and pressure Solubility equilibrium is a dynamic equilibrium between a solute and a solvent that occurs in a saturated solution A solubility equilibrium is a heterogeneous equilibrium system between a solid ionic compound and its ions dissolved in a saturated aqueous solution A solubility product constant is the value obtained from the equilibrium law applied to a saturated solution. It is the value for a solubility equilibrium. The solubility of an ionic compound varies with the ions it contains. Basically, the more highly charged the anions and cations are, the less soluble the ionic compound will be because it takes more energy for a solvent to break the ionic bonds in the crystal lattice. Divalent ions in ionic compounds, such as calcium (Ca2+) are usually less soluble than something monovalent like sodium (Na+). Keep in mind that the solubility of a given ionic compound is different from its solubility product constant. The solubility of an ionic compound simply tells us the maximum quantity that will dissolve in a given volume of solvent at a particular temperature to form a saturated solution. Meanwhile, the solubility product constant of that compound will be set to always the same constant. The SP is the equilibrium constant while the solubility would be the X that goes into the ICE table. Basically, the SP is the ratio and the molar solubility is the specific concentration of the ions that are plugged into the Ksp formula. The trial ion product(Q) is the reaction quotient applied to the initial ion concentration of a slightly soluble ionic compound Note that we always write the equilibrium reaction equation so that the dissolution reaction occurs to the right 8.1 Notes: The Arrhenius theory is a theory stating that in an aqueous solution and acid is a substance that  produces hydrogen ions, and a base is a substance that produces hydroxide ions This theory was limited because it allowed for only one kind of base - compounds containing the hydroxide ion - and it assumed that all acid-base reactions occur in aqueous solutions The Bronsted-Lowry theory states that an acid is a hydrogen (proton) ion donor and a base is a hydrogen ion acceptor (proton) Water is a Bronsted-Lowry base because it accepts a proton from the hydrogen fluoride molecule in the HF dissolving example In general, the Bronsted-Lowry bases contain at least one atom with one or more lone electron pairs (most often, O, N, or P) Since acid base reactions are reversible, a hydrogen ion (proton) transfer may occur in the forward reaction and also in the reverse reaction A conjugate acid is an acid formed when a base accepts a hydrogen ion from an acid. A conjugate base is a base formed when an acid loses a hydrogen ion to a base. For any acid base reaction, there will always be one conjugate acid based pair made up of an acid and its conjugate base and another conjugate acid base pair made up of a base and its conjugate acid Note that a substance can be classified as an acid or a base according to the Bronsted-Lowry theory only for specific reaction; however, a substance may act as an acid in one reaction and a base in another reaction. Again, the hydrogen fluoride example, where water is a base but in ammonia, water is a acid. Substance that may act as a Bronsted-Lowry acid in some reactions and as a Bronsted-Lowry base in others is called amphiprotic (or amphoteric). For example, water and the hydrogen carbonate ion (HCO3) are amphiprotic (able to both donate or accept a hydrogen ion (proton) The equilibrium constant for the ionization of an acid, also called the acid disassociation constant 8.2 Notes: when acids dissolve in water, they form a dynamic equilibrium between reactants and products. A strong acid is an acid for which the equilibrium position in an aqueous solution likes far to the right A weak acid has the position far to the left (a weak acid ionizes only to a very small extent) The stronger an acid, the weaker its conjugate base, and conversely, the weaker an acid, the stronger its conjugate base Strong bases almost dissolve entirely, NaOH for example. All hydroxides of group 1 and group 2 elements are strong bases. Alkaline bases are strong, but slightly soluble, and low solubility prevents a quick dissociation A base like ammonia doesn’t need hydroxide, but may increase the concentration of hydroxide ions in aqueous solutions because of their reaction with water (Bronsted-Lowry Bases) Weak base: a base that only partially reacts with water to produce hydroxide ions Weak bases are the conjugate bases of weak acids. Autoionization of water: the transfer of a hydrogen ion from one water molecule to another. The products are a hydrogen ion and a hyrdonium ion The ion-product constant for water is the equilibrium constant for the autoionization of water In any aqueous solution at 25 degrees C, no matter what the solution contains, the the product of [H+] and [OH-] must always equal 1.0 x 10-14 Ka x Kb = Kw A pH meter has a probe that can be inserted into a solution and it allows hydrogen ions to pass through. Displays the pH electronically When you put a base in pure water, the extra hydroxide ions will react with the hydrogen ions and subsequently lessen the concentration of hydrogen ions from 1.0 x 10-7 while the hydroxide concentration will increase from 1.0 x 10-7 8.4 Textbook Notes:.