Question

When a graph of energy vs, reaction progress was graphed for the reaction A + B rightarrow C + D, the following data was obtained: a) Draw a rough sketch of what this activation energy diagram looks like. Make sure axes and points are labeled appropriately. B) What is the numerical value of the activation energy obtained from the graph? c) Are reactants or products more stable? d) Is the reaction endothermic or exothermic? Explain. d) On the graph you drew in part A, show an example of what the reaction could look like if a catalyst was added. A reaction, A + 2B rightarrow C + D, was nun in a laboratory setting. Given the following plausible reaction mechanism, answer the questions below: Elementary step 1: A + B rightarrow I (slow step) Elementary step 2: I + B rightarrow C + D (fast step) a) What is the rate law that was experimentally determined? Explain. b) What is/are the reaction intermediates? c) If the speeds of the elementary steps were switched (i.e. elementary step 1 was fast and elementary step 2 was slow), could this reaction mechanism still be plausible? Explain.

Answer 1

3)


4)
a) The slow step is always the rate-determining step in the experiment,
rate law = K [A] [B]
b) I is the only reaction intermediate.
c) In 2 steps equilibrium steps such as those given in question, intermediate concentrations are
   somehow connected to reactant concentrations. So, even if the speeds are switched the
   mechanism will be plausible only when reasonable order (correct) is obtained.

(b) Activation Energy E_a = 140 kJ - 100 kJ = 40 kJ (c) products are at lower energy than Reactants [E_R > E_P] Therefore products are more stable [Exothermic Reaction]. (d) Exothermic Reaction Delta E = E_P - E_R = 40 - 100 = -60 kJ downarrow negative sign. 4) a) The slow step is always the rate-determining step in the experiment, rate law = K [A] [B] b) I is the only reaction intermediate. c) In 2 steps equilibrium steps such as those given in question, intermediate concentrations are somehow connected to reactant concentrations. So, even if the speeds are switched the mechanism will be plausible only when reasonable order (correct) is obtained.