Question

$\Delta H\&\Delta S$ for a reaction are $+30.0kJmo{l}^{-1}$ and $0.06kJ{K}^{-1}mo{l}^{-1}$ at $1atm$ pressure. The temperature at which free energy change is equal to zero and nature of the reaction below this temperature are

• A. $500{}^{\circ }C$ and non-spontaneous
• B. $227^{\circ }C$ and non-spontaneous
• C. $400{}^{\circ }C$ and spontaneous
• D. $127^{\circ }C$ and spontaneous

Answer 1

Answer: (B)

Given
$\Delta H=+30.0kJmo{l}^{-1}$
$\Delta S=0.06kJ{K}^{-1}mo{l}^{-1}$
$p=1atm$
$\Delta G=0$
We know that,
$\Delta G=\Delta H-T\Delta S$
$\Rightarrow 0=\Delta H-T\Delta S$
if, we put temperature $227^{\circ }C$
or $227+273=500K$
In equation then the value of free energy is obtained will be zero.
Hence, $\Delta G=30-500\times 0.06$
$\Delta G=30-30=0$
and nature of reaction will be non-spontaneous.