Reaction Kinetics Cheat Sheet

Kinetics H2 CHEMISTRY ORDERS OF REACTION RATE EQUATION DEFINITIONS CONTINUOUS METHOD QUESTIONS Question: Consider the reaction 2A + B → C. A couple of experiments wereconducted to study the reaction kinetics. B is kept in excess for all experiments.Find the order of reaction with respect to A and B. Observations Order of reaction When [A] is doubled, the rate ofreaction doubles Rate ∝ [A]Reaction is first order with respect to [A] When [A] is doubled, the rate ofreaction quadruples Rate ∝ [A]²Reaction is second order with respect to [A] When [A] is doubled, the rate ofreaction does not change Rate ∝ [A] ⁰Reaction is zero order with respect to [A] Term Definition Rate equation An experimentally-determined equation that relates the rate of reactionto the concentrations of the reactants raised to the appropriate orders. Order of Reaction The power on a reactant’s concentration term in the rate equation. Thispower is determined experimentally. Overall Order ofReaction The sum of the individual orders. k The proportionality constant in the experimentally-determined rateequation. INITIAL RATE METHOD QUESTIONS Consider the reaction 2A + B → C. A couple of experiments were conducted to find the order of reaction with respect to A and B. Exp V of A /cm³ V of B /cm³ V of H ₂ O/cm³ Initial rate 1 5 5 10 1.0 2 5 10 5 2.0 3 10 10 0 8.0 Therefore, rate = k[A]²[B] This is to ensure that total volume remains constant. Whentotal volume is constant, the concentration of reagents isproportional to volume ( [A] ∝ V of A. When volume doubles,concentration doubles). What is the rate equation? Comparing experiments 1 and 2, where [A] is constant, when [B]doubles, the initial rate doubles. Therefore, reaction is first orderwith respect to [B].Comparing experiments 2 and 3, where [B] is constant, when [A]doubles, the initial rate increases by 4 times. Therefore, reactionis second order with respect to [A]. Why must water be added to experiments 1 and 2? If order ofreaction w.r.tA is... Zero Order First Order The[reactant]-time graphwould looklike... Answeringtechnique The [A] decreases linearly overtime. This suggests that thedecrease in [A] has no effect onthe rate of reaction. *find two half-lives: 100% → 50% and 50%→ 25%*Since, half-life is constant at 10 min,reaction is first order w.r.t. [A]. The[product]-time graphwould looklike... Answeringtechnique The [C] increases linearly overtime. This suggests that thedecrease in [A] has no effect onthe rate of reaction. *find final [C] (100%) + two half-lives: 0%→ 50% and 50% → 75%*Since, half-life is constant at 10 min,reaction is first order w.r.t. [A]. [A] time [A] time 100% 50% 25% 1010 [C] time [C] time 100% 50%75% 1010 If order ofreaction w.r.t Bis... Zero Order First Order The [reactant]-time graphwould look like... The [product]-time graphwould look like... Answeringtechnique When the [B] halves, the initialrate of the reaction did notchange. This suggests that thedecrease in [B] has no effect