Question

t00 80 ner (k 60 40 20 Reaction Progress The diagram above represents the energy profile for the reaction: A + B - C +D. What is the value of the activation energy for the reaction: C+D—+A+B? (A) 25 kJ (B) 55 kJ (C) 85 kJ (D) -30kJ What is the equilibrium expression for this reaction? 2 HgO(s)-2 Hg(1) + O2(g) (A) K (Hg)[02] [HQ] (B) K [Hg] [02] [HgQ]2 (C)K-- [Hg]’to 2] (D) K [ 2]

Answer 1

1-

Activation energy is that energy which is required to raise the energy of reactant to the transition state, so as to form a product finally. In the reaction coordinate, activation energy is the energy level difference between transition state energy and reactant energy.

The given reaction is : A + B ----> C + D
Hence reactants are - A + B which are at energy level = 40kJ (approx)
products are- C+ D which are at energy level = 60kJ
And transition state is at energy level = 85kJ (Approx)

In the reaction coordinate it is denoted as:  

TS t00 85 80 ner (k F 60 C+D 40 A+B 20 Reaction Progress

Activation energy for reaction: A+ B ---> C +D is equal to : 85kJ - 40kJ = 45 kJ

Now for reaction C+ D --> A + B , same reaction coordinate can be used, just that the reactant is C+ D and transition state remains the same. Its activation energy is as:

TS t00 85 80 ner (k F 60 CAD 40 A+B 20 Reaction Progress

So, activation energy for C + D --> A + B is equal to 85kJ - 60 kJ = 25 kJ

Correct answer is option A - 25kJ

2-

For any reaction: aA + bB --> cC + dD, equilibrium constant is written as:

$K = \frac{[C]^{c}[D]^{d}}{[A]^{a}[B]^{b}}$ , where [A], [B], etc are equilibrium concentration of respective species.

So, we basically, have to write products in numerator - raised to powers equal to their stoichiometric coefficient and write reactants in denominator- raised to powers equal to their stoichiometric coefficient.

Also, note that pure solids and pure liquids do not appear among these species in the equilibrium constant, as their concentration remains constant.

Here, reaction is:

2 HgO(s) 2 Hg(1) + O2(g)

Note that HgO is pure solid and Hg is pure liquid.

So, equilibrium constant should contain only O₂ in its expression. Therefore, K = [O₂] for this reaction.

Correct answer is option D- K = [O₂]