The equation [tex]$CaCO_3(s) \rightarrow CaO(s) + CO_2(g)$[/tex] shows the decomposition of calcium carbonate.

Given:
- [tex]$\Delta H = 178.3$[/tex] kJ/mol
- [tex]$\Delta S = 160.5$[/tex] J/(mol·K)
- The free energy change for the reaction is [tex]$\Delta G = 130.5$[/tex] kJ/mol

Which correctly states the temperature at which the reaction took place and whether the reaction is spontaneous or nonspontaneous? Use [tex]\Delta G = \Delta H - T \Delta S[/tex].

A. 0.30 K, spontaneous
B. 1.92 K, spontaneous
C. 297.8 K, nonspontaneous
D. 1924 K, nonspontaneous



Answer :

To determine the temperature at which the reaction took place and whether the reaction is spontaneous or nonspontaneous, we can use the Gibbs free energy equation:

[tex]\[ \Delta G = \Delta H - T \Delta S \][/tex]

### Step-by-Step Solution:

1. Given Data:
- [tex]\(\Delta H = 178.3 \,\text{kJ/mol}\)[/tex]
- [tex]\(\Delta S = 160.5 \,\text{J/(mol·K)}\)[/tex]
- [tex]\(\Delta G = 130.5 \,\text{kJ/mol}\)[/tex]

2. Convert [tex]\(\Delta S\)[/tex] into kJ/(mol·K):
- Since 1 kJ = 1000 J, we convert [tex]\(\Delta S\)[/tex] from J/(mol·K) to kJ/(mol·K).
[tex]\[ \Delta S = 160.5 \,\text{J/(mol·K)} = 0.1605 \,\text{kJ/(mol·K)} \][/tex]

3. Rearrange the Gibbs Free Energy equation to solve for temperature, [tex]\( T \)[/tex]:
[tex]\[ T = \frac{\Delta H - \Delta G}{\Delta S} \][/tex]

4. Substitute the values into the equation:
[tex]\[ T = \frac{178.3 \,\text{kJ/mol} - 130.5 \,\text{kJ/mol}}{0.1605 \,\text{kJ/(mol·K)}} \][/tex]

5. Calculate the numerator:
[tex]\[ 178.3 - 130.5 = 47.8 \,\text{kJ/mol} \][/tex]

6. Divide by [tex]\(\Delta S\)[/tex]:
[tex]\[ T = \frac{47.8 \,\text{kJ/mol}}{0.1605 \,\text{kJ/(mol·K)}} = 297.8 \,\text{K} \][/tex]

7. Determine the spontaneity of the reaction:
- A reaction is spontaneous if [tex]\(\Delta G < 0\)[/tex], and nonspontaneous if [tex]\(\Delta G > 0\)[/tex].
- Given [tex]\(\Delta G = 130.5 \,\text{kJ/mol}\)[/tex], the reaction is nonspontaneous as [tex]\(\Delta G > 0\)[/tex].

### Conclusion:
The correct temperature at which the reaction took place is approximately [tex]\(297.8 \,\text{K}\)[/tex], and since [tex]\(\Delta G\)[/tex] is greater than zero, the reaction is nonspontaneous. Therefore, the correct statement is:

- [tex]\(297.8 \,\text{K}\)[/tex], nonspontaneous