Question

Metallic mercury is obtained by roasting mercury (II) sulphide in a limited amount of air. Estimate the temperature range in which the standard reaction is product - favoured.
$HgS\left(s\right)+O_2\left(g\right)\to Hg\left(l\right)+S{O}_2\left(g\right)$
$△H^o=-238.6kJ/moleand△S^o=+36.7J/mole\cdot K$

• A. When $T>200K$
• B. When $T>300K$
• C. At all temperatures
• D. None of these

Answer 1

The correct option is C At all temperatures

Assume that $△Hand△S$ values do not depend on temperature.

As $△H^0$ is negative and $△S^0$ is positive, using the equation $△G^0=△H^0-T△S^0$

$△G^0$ should be negative so the reaction is product-favoured.

$\Rightarrow △H^0-T△S^0<0$

In the question $△H^0$ is negative and $△S^0$ is positive and we know temperature is always positive. So, $△H^0-T△S^0$ will be negative for all temperatures.