Question

For the reaction $H_2\left(g\right)+I_2\left(g\right)\rightleftharpoons 2HI\left(g\right)$ $K_i=66.9$ at ${350}^o$C and $K_i=50.0$ at ${448}^o$C. The reaction has:

• A. $\Delta H=+$ve
• B. $\Delta H=-$ve
• C. $\Delta H=$zero
• D. none of the above

Answer 1

Answer: (B)

$\Delta H=-$ve

Solution:- (B) $\Delta H=-ve$

Given:-

$K_i$ at $350℃=66.9$

$K_i$ at $448℃=50.0$

As the ionisation constant is decreasing with increase in temperature, i.e., the reaction is exothermic. Hence $\Delta H$ will be negative.