The following elementary reactions have known standard entropy changes

CHEMISTRY · Single correct · A Level · Chemistry · Thermodynamics · Thermodynamics

Problem

The following elementary reactions have known standard entropy changes. (1)

\displaystyle \text{CaCO}_3(s) \rightarrow \text{CaO}(s) + \text{CO}_2(g) \qquad \Delta S_1^\circ = +160.5\,\text{J\,mol}^{-1}\,\text{K}^{-1}

(2)

\displaystyle \text{CaO}(s) + \text{H}_2\text{O}(l) \rightarrow \text{Ca(OH)}_2(s) \qquad \Delta S_2^\circ = -83.4\,\text{J\,mol}^{-1}\,\text{K}^{-1}

What is

\Delta S^\circ

for the overall reaction?

\displaystyle \text{CaCO}_3(s) + \text{H}_2\text{O}(l) \rightarrow \text{Ca(OH)}_2(s) + \text{CO}_2(g)

(a)

+243.9\,\text{J\,mol}^{-1}\,\text{K}^{-1}

(b)

-6.3\,\text{J\,mol}^{-1}\,\text{K}^{-1}

(c)

+77.1\,\text{J\,mol}^{-1}\,\text{K}^{-1}

(d)

-77.1\,\text{J\,mol}^{-1}\,\text{K}^{-1}