Question

1. Consider the three reaction energy diagrams below. Make sure you can justify your answer for the purposes of Exam 3 - simply guessing on this multiple choice question will NOT help you when you're asked to explain your reasoning on the exam! energy- energy- reaction coordinate reaction coordinate reaction coordinate i) Which forward reaction do you expect to proceed fastest, assuming the same energy scale for each? ii) Which reaction do you expect to be the most favorable in the forward direction, assuming the same energy scale for each? iii) Which energy diagram would you expect to have the largest Keq, assuming the same energy scale for each? iv) Which energy diagram would you expect to have the smallest Keq, assuming the same energy scale for each? v) Which reaction has a transition state that most resembles the structure of the product? vi) Which reaction has the largest negative AG? (ie, AG<0) A. i) = Y, ii) = Z, iii) = Z, iv) = X, v) = X, vi) - Z B. i) = Y, ii) = Z, iii) = X, iv) = Z, v)=X, vi) - Z C. i) = Z, ii) = X, iii) = X, iv) = Z, v) = Z, vi)=Y D. i) = Y, ii) = Z, iii) = Z, iv)-X, v)=Y, vi) =Y E. i) = X, ii) = Y, iii) = Z, iv) = Y, v)=X, vi) - Z F. i) = X, ii) = Y, iii) = Z, iv) = Y, v)=X, vi) = X

Answer 1

The correct answer is option: A

(i) Among the given three graphs the fastest forward reaction is shown by graph-Y because here first the gibbs free energy is negative unlike graph-X where it is positive and also its activation energy (amount of energy required to cross the energy barrier is low) compared to graph-Z therefore thhe fastest forward reaction is shown by graph-Y.

(ii) Most favourable reaction among the three graphs is graph-Z because first the change in gibbs free energy is negative and second the product occupies lowest energy state.

(iii)Equillibrium constant (K_eq) value is directly proportional to temperature thus if heat is released out as that in exothermic reactions than the equillibrium constant will increase, thus the graph-Z is expected to have the maximum K_eq value.

(iv) Similarly, for endothermic reactions in which heat is required possess minimum equilibrium constant value, thus the graph-X shows smallest K_eq value.

(v) Endothermic reaction has a transition state that most resembles the structure of product thus the answer is graph-X.

(vi) The distance between the energy states of reactants and products is maximum in the case of graph-Z because of the largest activation energy barrier thus the largest negative gibbs free energy value is for graph-Z.