Question

Consider a reaction that has a negative ΔH and a positive ΔS. Which of the following statements is true?

Options:

1. This reaction will be spontaneous only at high temperatures.
2. This reaction will be spontaneous at all temperatures.
3. This reaction will be nonspontaneous at all temperatures.
4. It is not possible to determine without more information.
5. This reaction will be nonspontaneous only at high temperatures.
Options:
a. 1 and 3
b. 2 and 5
c. 1 and 4
d. 2 and 3

Answer 1

A reaction with negative ΔH and positive ΔS will be spontaneous at all temperatures because the Gibbs free energy (ΔG) will be negative at any temperature.

Step-by-step explanation:

If we consider a reaction that has a negative ΔH (enthalpy change) and a positive ΔS (entropy change), the Gibbs free energy (ΔG) equation, which is ΔG = ΔH - TΔS, can be used to determine the spontaneity of the reaction. Since temperature (T) is always positive (as it is measured in Kelvin in thermodynamics), the ΔS term will also be positive when multiplied by the temperature. Thus, we will have a negative ΔH and a negative TΔS term, which means that the value of ΔG will be negative at any temperature, and therefore, the reaction will be spontaneous at all temperatures.

According to the options presented in the question, this corresponds to the statement that 'this reaction will be spontaneous at all temperatures'. Therefore, the only true statement among the given options is number 2: This reaction will be spontaneous at all temperatures.