Consider a reaction that has a positive ΔH and a positive ΔS. Which of the following statements is TRUE? A. This reaction will be spontaneous only at high temperatures. B. This reaction will be nonspontaneous at all temperatures. C. This reaction will be spontaneous at all temperatures. D. This reaction will be nonspontaneous only at high temperatures. E. It is not possible to determine without more information.

E

Explanation:

The spontaneity of a reaction is basically dependent on the value of the change in free energy written symbolically as ΔG.

For a reaction to be spontaneous, this value must be negative. To compute the value, we need some very important information. We need the temperature of the system, the entropy value and the change in enthalpy. These are related by the formula

ΔG = ΔH - T ΔS

We are told to consider a reaction that has a positive ΔH and ΔS, this means that for the change in free energy to be negative, we need to know the value of the temperature.

Unfortunately, we do not know how positive they both are, I. e the magnitude of their positive value and thus we cannot say with certainty of the value of the change in free energy will be positive or negative. Thus we need more information and cannot predict accurately the spontaneity of the reaction with the information presented.