Question

The heat of reaction for an endothermic reaction at constant volume in equilibrium is $1200cal$ more than the heat of reaction at constant pressure at $300K$. Calculate the ratio of equilibrium constants $K_p$ and $K_c$.

• A. $1.648\times {10}^{-3}$
• B. $2.658\times {10}^{-3}$
• C. $1.848\times {10}^{-3}$
• D. None of these

Answer 1

Answer: (A)

$1.648\times {10}^{-3}$

Given that: $\Delta U-\Delta H=1200cal$

where $\Delta U$ is the heat of reaction at constant volume and $\Delta H$ is the heat of reaction at constant pressure.

Also, we have $\Delta H=\Delta U+\Delta nRT$

$\therefore \Delta nRT=-1200$

or $\Delta n=\frac{-1200}{2\times 300}=-2$ $(R=2cal)$

Now, $K_p=K_c{\left(RT\right)}^{\Delta n}$

$\therefore \frac{K_p}{K_c}={(0.0821\times 300)}^{-2}=1.648\times {10}^{-3}$