Question

Consider the following hypothetical chemical reactions. All of them have the same heat of reaction. The activation energies for the forward and bacward processes are also the same in all cases. Which of these chemical reactions is likely to reach a larger extent at equilibrium (i.e., a larger fraction of products present in the equilibrium mixture)?

Answer 1

If same Heat of reaction

assume

enthalpy = Hrxn

same kinetics so ignore that, that has nothing to do with equilibrium

entropy = more mol of gas, more entropy generation

Then, according to Gibbs

G = H - TS

if in all cases H is the same, we might ignore, let us concentrate in TS term

assume same temperature so

only S is a factor

in order to G to be in forward reaction, it mus be negative i.e. G < 0

that is

G = H - TS = S (according to our study)

so

S > 0

S generation must be HIGH

so

A)

3 mol of gas turn to 2 mol o fgas, decrease

B)

3 mol of gas = 4 mol of gas, increase

3 mol of gas = 3 mol of gas, same

Therefore, choose B, since mol of gas increase, that is, entropy increase, therefore -TS increases and G is likely to be forward