Question

For a reaction that has a positive value of ΔH and a negative value of ΔS, which statement is true at equilibrium?

a) Reactants are favored at very low temperatures and reactants are favored at very high T

b) Reactants are favored at very low temperatures and products are favored at very high T

c) Products are favored at very low temperatures and reactants are favored at very high T

d) Products are favored at very low temperatures and products are favored at very high T

Note: “Reactants are favored” means they are present at equilibrium in greater amounts than products.

Answer 1

option a

When delta H is positive it is endo thermic reaction , not favorable for formation of products.

delta S is also negative which is again not favorable for product formation.

We know

delta G = delta H - T.delta S

for a reaction to be spontaneous (favorbale in the given direction) delta S has to be negative.

However the givendelta H positive and delta S negative can never give a negative value for Delta G (at low or high temperatures).

Thus the reaction remains non-spontaneous at all temperatures, which means it is reactant favored at all temperatures.

Thus option a

reactants are favored at very low temperatures and reactants are favord at very high temperature is correct.