A certain homogenous gas-phase reaction is exothermic and proceeds with an increase in the number of moles of gas. Which of the following statements concerning this reaction is true?

Options

A. This reaction is spontancous at lower temperatures but non-spontancous at higher temperatures.
B. This reaction is is non-spontaneous over all possible temperatures
C. This reaction is is spontancous over all possible temperatures
D. There is a temperature at which this reaction can be at equilibrium where all species are present at standard concentrations.

Answer

To solve the problem, we need to analyze the given information about the reaction and apply the principles of thermodynamics, particularly focusing on Gibbs free energy and the relationship between enthalpy, entropy, and temperature.

### Step-by-Step Solution:

1. **Identify the Nature of the Reaction**:
- The reaction is described as exothermic, which means that the change in enthalpy (ΔH) is negative (ΔH < 0).
- The reaction also proceeds with an increase in the number of moles of gas, indicating that the entropy (ΔS) of the system increases (ΔS > 0).

2. **Write the Gibbs Free Energy Equation**:
- The Gibbs free energy change (ΔG) for a reaction is given by the equation:
\[ \Delta G = \Delta H - T \Delta S \]

3. **Substitute the Values**:
- Since ΔH is negative and ΔS is positive, we can substitute these values into the Gibbs free energy equation:
\[ \Delta G = \text{(negative)} - T \times \text{(positive)} \]
- This implies that ΔG will always be negative for any positive temperature (T), since both terms contribute to making ΔG negative.

4. **Conclusion on Spontaneity**:
- A negative ΔG indicates that the reaction is spontaneous. Therefore, since ΔG is negative at all temperatures, we conclude that the reaction is spontaneous at all temperatures.

5. **Evaluate the Statements**:
- We need to evaluate the provided statements regarding the spontaneity of the reaction:
- **Statement 1**: This reaction is spontaneous at lower temperatures, but non-spontaneous at higher temperatures. (Incorrect)
- **Statement 2**: This reaction is non-spontaneous at all temperatures. (Incorrect)
- **Statement 3**: This reaction is spontaneous at all temperatures. (Correct)
- **Statement 4**: This reaction is spontaneous only at higher temperatures. (Incorrect)

6. **Final Answer**:
- The correct statement concerning this reaction is that it is spontaneous at all temperatures.