General Chemistry 1 Final Examination (OCR) PDF

The change in the concentration of a GENERAL reactant or a product with time CHEMISTRY 1 One mole of A disappear for each mole...

The change in the concentration of a GENERAL reactant or a product with time CHEMISTRY 1 One mole of A disappear for each mole of B that is formed FINAL EXAMINATION UNIT: Molarity per Second [M/s] Term 1: 2nd Quarter ○ Can be any unit if problem does ⓒ Academics, Secretariat, and not indicate that it needs to be Pool-of-Staff Committee M/s TOPIC OVERVIEW GENERAL EQUATION 1. CHEMICAL KINETICS A→B Rate of a Reaction Factors that influence Rate of As the reaction progresses, Reactant Reaction decrease and Product increases The Collision Theory The Rate Laws Reaction Mechanism ↱ if reactant ↱ if product Half Life ∆[𝐴] ∆[𝐵] Catalysis 𝑅𝑎𝑡𝑒 =− ∆𝑡 or = ∆𝑡 2. CHEMICAL EQUILIBRIUM The Equilibrium Condition Writing the Reaction LEGENDS: Quotient/Equilibrium Constant Expression ○ ∆ = Final - Initial Predicting the Direction of a ○ [] = Concentration Reaction Calculating the Equilibrium ○ A = Reactant Concentrations in Reversible ○ B = Product Reaction Le Chatelier’s Reaction ○ t = Time ○ - = Left and Downward, used the reactant. LESSON 1: CHEMICAL KINETICS ○ + = Right and Upward, used the Product. Area of Chemistry concerned with the speed or rate at which a chemical reaction occurs ❗ Magnitude of Reaction Rate can NEVER be negative. The signs used in the solution are purely for showing if reactant 01 REACTION RATE [-] or product [+] is used in the solution.  02 RATE EXPRESSION Equation used for Reaction Rate when NO CONCENTRATION is given but 1 03 COLLISION THEORY compound has a given reaction rate Two moles of A disappear for each mole of B that is formed For a reaction to occur, molecules must collide GENERAL EQUATION Explains why chemical reactions have different reaction rates. 2A → B ↑ Molecules Present ;↑ Collisions ;↑ Rate aA + bB → cC + dD ○ Lowercase letters denote the REQUIREMENTS FOR A CHEMICAL REACTION stoichiometric coefficients ＞ 1 𝑅𝑎𝑡𝑒 =− 1 ∆[𝐴] =− 1 ∆[𝐵] = 1 ∆[𝐶] = 1 ∆[𝐷] Reacting Particles Collide 𝑎 ∆𝑡 𝑏 ∆𝑡 𝑐 ∆𝑡 𝑑 ∆𝑡 Sufficient Energy Rate Expression: ○ At least equal to the Activation 1 ∆[𝐴] ∆[𝐵] 𝑅𝑎𝑡𝑒 =− 2 ∆𝑡 = ∆𝑡 Energy ○ Activation Energy (Ea) - EXAMPLE Consider the reaction: Minimum energy required to 4 𝑁𝑂2( 𝑔) + 𝑂2 ( 𝑔) → 2 𝑁2𝑂5( 𝑔) initiate a chemical reaction Correct orientation Suppose that, at a particular moment during the reaction, molecular oxygen is reacting at ○ The Orientation Factor - Similar the rate of 0.024 M/s. to the lock & key model. Affects a.) At what rate is 𝑁2𝑂5 being formed? the effectiveness of the collision ★ Used the long method 04 FACTORS AFFECTING REACTION RATE CONCENTRATION OF REACTANTS An increased concentration yields more b.) At what rate is 𝑁𝑂2 reacting? reactants and less spaces between ★ Used the more efficient formula to get the reaction rate them allowing for more collisions per 𝐷𝑒𝑠𝑖𝑟𝑒𝑑 𝐶𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 ○ 𝐺𝑖𝑣𝑒𝑛 𝑅𝑅 𝑥 𝐺𝑖𝑣𝑒𝑛 𝐶𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡  unit area that induce a chemical 05 MONITORING KINETICS reaction SPECTROMETER TEMPERATURE Measures the absorption through the Increasing the temperature directly wavelength. increases the frequency of collisions and the fraction of the collisions that have MANOMETER sufficient energy to be effective. Measures Pressure PHYSICAL STATE OF REACTANTS Applicable for Gas samples only throughout a chemical reaction. Solid ○ Particles are Restricted in their 06 RATE LAW motion ○ SLOWEST Gas & Liquid Expresses the relationship of the rate of a ○ Particles have Free Motion reaction to the rate constant and the ○ FASTEST concentration of the reactants raised to some powers PRESENCE OF A CATALYST Always determined experimentally A presence of a catalyst increases the GENERAL FORM Reaction Rate ○ Acids A + B → Products 𝑥 𝑦 ○ Metals 𝑅𝑎𝑡𝑒 = 𝑘[𝐴] [𝐵] ○ Enzymes ○ k = Rate Constant ○ x = Rate Order of Reactant A SUMMARY ○ y = Rate Order of Reactant B Concentration of Reactants ↑ C ↑ RR x + y = Overall Rate Order Temperature ↑ T ↑ RR Physical State of Reactants ↑ SA ↑ RR 6.1 REACTION ORDER Presence of Catalyst Ca ↑ RR Determines how concentration of reactants affect reaction rate  EXAMPLE REACTION ORDER Determine rate law for this reaction: Zero Order Reaction Rate is NOT 𝐹2 ( 𝑔) + 2𝐶𝑙𝑂2 ( 𝑔) → 2𝐹𝐶𝑙𝑂2 ( 𝑔) dependent on the Table 1 Rate Data for Reaction between 𝐹2 and 𝐶𝑙𝑂2 concentration of reactants Trial # [𝐹2] (𝑀) [𝐶𝑙𝑂2] (𝑀) Initial Rates (M/s) No effect at all 1 0.10 0.010 0.0012 2 0.10 0.040 0.0048 Exponent is 0 3 0.20 0.010 0.0024 0 0 0 2 = 1 ; 5 = 1 ; 10 = 1 a.) Determine Reaction Order of [𝐴] 𝑥 ★ Reactant A should have a CHANGE ★ Reactant B should be CONSTANT 𝑦 b.) Determine Reaction Order of [𝐵] Fir st Order Doubling the concentration of ★ Reactant A should be CONSTANT reactant causes the rate to ★ Reactant B should have a CHANGE double c.) Determine Overall Reaction Order Exponent is 1 1 1 1 2 = 2 ; 5 = 5 ; 10 = 10 Second Doubling the concentration Order of reactant causes the rate to quadruple Exponent is 2 2 2 2 2 = 4 ; 5 = 25 ; 10 = 100 Reaction Order Rate M/t Unit of k Overall Sum of the reaction orders of 0 Zero 𝑘[𝐴] 𝑘 𝑀/𝑠 Reaction ALL the reactants 1 −1 First 𝑘[𝐴] 𝑘𝑀 𝑠 Order Second 2 𝑘[𝐴] 𝑘𝑀 2 1/𝑀. 𝑠 𝑜𝑟 𝑀 𝑠 −1 −1 x+y 6.2 INTEGRATED RATE LAW 08 REACTION MECHANISM Rate Law with Time & Utilizes calculus Detailed steps of the reaction that occur at a molecular level OVERALL RATE LAW CONCENTRATION - A sequence of elementary steps or so ORDER TIME called details of the journey towards the 0 𝑅𝑎𝑡𝑒 = 𝑘 [𝐴]𝑡 = [𝐴]0 − 𝑘𝑡 final balanced equation 1 𝑅𝑎𝑡𝑒 = 𝑘[𝐴] 𝐼𝑛[𝐴]𝑡 = 𝐼𝑛[𝐴]0 − 𝑘 INTERMEDIATES 2 𝑅𝑎𝑡𝑒 = 𝑘[𝐴] 2 1 [𝐴]𝑡 = 1 [𝐴]0 + 𝑘𝑡 Species that appears in a reaction mechanism but NOT in the overall ○ In = Natural Logarithm (𝑙𝑜𝑔𝑒) balanced equation ○ e = 2.7183 Product at first, Reactant at the End ○ [𝐴]𝑡= Concentration at any given Neither an original reactant nor a final time product ○ [𝐴]0= Initial Concentration Overall balanced equation is written by ○ k= rate constant combining the species of the elementary ○ t= time steps that appear on both sides of the equation This also tells us the molecularity of the 07 HALF-LIFE elementary step ○ Unimolecular - 1 GENERAL FORM ○ Bimolecular - 2 ○ Termolecular - 3 Time taken for the concentration of a reactant to drop to HALF of its original 3.1 IN RELATION TO RATE LAW value ↑ k = ↑ Rate = ↓ Half Life Reaction Order is equal to the Coefficient of the elementary step. 𝐼𝑛2 𝑡1 = 𝑘 TYPE ELEM STEP RATE 2 Uni 𝐴→𝑝𝑟𝑜𝑑𝑢𝑐𝑡 𝑟𝑎𝑡𝑒 = 𝑘[𝐴] Bi 𝐴 + 𝐵→𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 𝑟𝑎𝑡𝑒 = 𝑘[𝐴][𝐵] ○ In 2 = approx. 0.693 Ter 𝐴 + 𝐴→𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 2 𝑟𝑎𝑡𝑒 = [𝐴] RATE DETERMINING STEP Reactants and Catalysts are at If more than 1 elem step, rate law is given different phases Initial step is by the rate-determining step or rate absorbtion of limiting step. reactants SLOWEST STEP in all the steps leading to ○ Absorbtion = product formation Binding of ○ ANALOGY molecules to Traffic on a narrow road. the surface Cars can't move past ○ Absorption = Uptake of each other, rate at which molecules into a car travels is interior of a determined by the slowest substance moving car Enzymes Biological catalysts Slowest moving car is the Increase rate by 6 18 rate determining step 10 − 10 Highly specific 09 CATALYSIS ○ Acts only on substrates or reactant and A catalyst is a substance that increases leave the rest the rate of a chemical reaction without of the system itself being consumed unaffected Lowers the Activation energy for a reaction and Create a different pathway LESSON 2: CHEMICAL EQUILIBRIUM (shortcut) from reactant to product that require less energy and therefore increasing reaction rate [#of collisions] Also known as dynamic equilibrium The state of a chemical reaction when TYPES OF CATALYST the concentration of the products and Homogenous Acids or Bases the reactants are unchanged over time Reactants are The forward rate of the reaction equals dispersed in a single the backward rate of the reaction phase Heterogenous Metals ○ Platinum, Gold Reactants are absorbed HOW IT REACHES EQUILIBRIUM Examples of this include gas reactions and solution reaction As substances A and B react, their HETEROGENEOUS EQUILIBRIUM concentrations fall ○ Particles are less likely to collide The components are present in more ○ Less rate of reaction than 1 phase As substances C and D react, their Examples of this include solid-gas concentrations increase reactions and solid-liquid reactions ○ Particles are more likely to collide therefore, more likely to react 2.1 EQUILIBRIUM CONSTANT EXPRESSION The rates of the 2 reactions will become equal as A and B convert to C and D at The value is always the same, exactly the same rate as C and D irrespective of the components A, B, C, convert back to A and B and D amounts. It is also unaffected by the change in pressure and whether or not there is a CONSTANT EXPRESSIONS catalyst Constants within the range of 0.01 to 100 KC → concentration indicate that a chemically significant KP → pressure amount of all components in the reaction system will be present in an 01 LAW OF MASS ACTION equilibrium mixture By Cato Maximillian Guldberg and Peter Waage The law of mass action states that the rate of a reaction is proportional to the active masses of each reacting substance. Make sure the equation is balanced before proceeding with the solution 02 TYPES OF EQUILIBRIUM DERIVING PRESSURE FROM HOMOGENEOUS EQUILIBRIUM CONCENTRATION All the components are present in the The components are present in more same phase than 1 phase  Kp = Kc(RT)Dn 04 LE CHATLIER’S PRINCIPLE Note that Dn is the difference in the number of moles of gasses on each side States that a system at equilibrium will of the balanced equation respond to any stress on that system to relieve it and establish a new equilibrium 02 CALCULATING EQUILIBRIUM Helps predict what change in CONCENTRATIONS temperature, pressure, and concentration will affect the reaction ICE TABLE Initial Change in Equilibrium 4.1 EFFECT OF CONCENTRATION STEP-BY-STEP GUIDE If concentration is increased, the 1. Note the initial concentrations of reactants equilibrium will shift so that the concentration decreases 2. Construct the a table in which we The equilibrium will shift towards the tabulate the initial concentrations direction of the reaction that uses a. TIP: Place the balanced equation as the heading of the reactants table to be guided 3. Use the stoichiometry of the reaction to determine the changes in 4.2 EFFECT OF TEMPERATURE concentration that occur as the reaction proceeds to equilibrium. If the temperature is increased, the a. Represent the change with x equilibrium will shift to decrease temperature 4. Use the initial concentration and its ○ It will favor the reaction using changes to express equilibrium changes more heat energy - the endothermic reaction 5. Substitute the equilibrium A decrease in temperature favors the concentrations into the equilibrium forward reaction - the exothermic constant expression and solve for x reaction because it produces energy 4.3 EFFECT OF PRESSURE When the pressure increases, the equilibrium will shift to a direction that  reduces the amount of particles so that pressure is reduced 4.4 EFFECT OF A CATALYST Does not change K Does not shift the position of an equilibrium system System will reach equilibrium sooner Catalyst lowers Ea for both forward and reverse reactions. Catalyst does not change equilibrium constant or shift equilibrium. EXAM TIPS: 1. Practice solving word problems prior to the exam, Chemistry is best learned through application. 2. Understand the formulas rather than memorizing, this will help you in deriving formulas. 3. Always keep an eye out for the SI units and SF utilized in the problem. PREPARED BY: Julee Austria Megan Bernice Aseron