Question

A reaction takes place in a several sequential steps $A$, $B,C$ and $D$. The value of enthalpy change for sequential steps are $p,q,r$ and $s$, respectively. If $B$ and $C$ have equal values of enthalpy change with total enthalpy change $t$, then choose the incorrect symbolic equation among the following.

• A. $q=r$
• B. $q+r=t-(s+p)$
• C. $2q=t-(s+p)$
• D. $q+r=p+s$

Answer 1

Answer: (D)

According to the question, the diagrammatic representation of given reaction can be

As given, $q=r$
[Hence, (a) is correct]
Using concept of Hess's law, $t=p+q+r+s$
$\therefore q+r=t-(s+p)$ [Hence, (b) is correct]
$2q=t-(s+p)$ [Hence, (c) is correct]
$[\because q=r]$
but $q+r=p+s$ is incorrect because exact amount of enthalpy change for each step is not given.