High School

Calculate the [tex]\Delta G[/tex] for the following system. Then state if the system is spontaneous or not spontaneous.

[tex]\[
\begin{array}{l}
\Delta H = 147 \, \text{kJ} \\
\Delta S = -67.0 \, \text{J/K} \\
T = 149^{\circ} \text{C}
\end{array}
\][/tex]

A. [tex]2.8 \times 10^4 \, \text{kJ}[/tex]; spontaneous
B. 175 kJ; not spontaneous
C. 157 kJ; not spontaneous
D. 175 kJ; spontaneous
E. [tex]2.8 \times 10^4 \, \text{kJ}[/tex]; not spontaneous
F. 157 kJ; spontaneous

Answer :

To solve for the Gibbs free energy change ([tex]$\Delta G$[/tex]) and determine the spontaneity of the process, we start with the formula:

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

Step 1. Convert Units (if necessary):

- The enthalpy change is given as [tex]$\Delta H = 147\,\text{kJ}$[/tex]. We need to convert this to joules since the entropy change ([tex]$\Delta S$[/tex]) is in joules per kelvin. Thus,

[tex]$$
\Delta H = 147\,\text{kJ} = 147\,000\,\text{J}.
$$[/tex]

- Temperature is given as [tex]$149^\circ\text{C}$[/tex]. Converting to Kelvin:

[tex]$$
T = 149 + 273.15 = 422.15\,\text{K}.
$$[/tex]

Step 2. Calculate [tex]$T\Delta S$[/tex]:

- The entropy change is given as [tex]$\Delta S = -67.0\,\frac{\text{J}}{\text{K}}$[/tex], so

[tex]$$
T\Delta S = 422.15\,\text{K} \times (-67.0\,\frac{\text{J}}{\text{K}}) \approx -28\,284.05\,\text{J}.
$$[/tex]

Step 3. Calculate [tex]$\Delta G$[/tex]:

Substitute the values into the formula:

[tex]$$
\Delta G = 147\,000\,\text{J} - (-28\,284.05\,\text{J}) = 147\,000\,\text{J} + 28\,284.05\,\text{J} \approx 175\,284.05\,\text{J}.
$$[/tex]

Convert [tex]$\Delta G$[/tex] back to kilojoules:

[tex]$$
\Delta G \approx \frac{175\,284.05\,\text{J}}{1000} \approx 175\,\text{kJ}.
$$[/tex]

Step 4. Determine Spontaneity:

A process is spontaneous if [tex]$\Delta G$[/tex] is negative. Here, [tex]$\Delta G$[/tex] is positive ([tex]$175\,\text{kJ}$[/tex]), which means the process is not spontaneous.

Final Answer:

[tex]$$
\Delta G \approx 175\,\text{kJ}; \quad \text{the system is not spontaneous}.
$$[/tex]

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