Question

The molar heat capacities at constant pressure (assume constant with respect to temperature) of $A,B$ and $C$ are in the ration of $1.5:3.0:2.0$.

If enthalpy change for the exothermic reaction $A+2B\to 3C$ at $300K$ is $-10kJ/mol$ & $C_{p,m}\left(B\right)$ is $300J/mol$ then enthalpy change at $310K$ is:

• A. $-8.5kJ/mol$
• B. $8.5kJ/mol$
• C. $-11.5kJ/mol$
• D. none of these

Answer 1

The correct option is C $-11.5kJ/mol$

$△H=n{C}_p△T$ and
$C_{p,m}\left(B\right)$ is $300J/mol$ so by their ration
$C_{p,m}\left(C\right)$ is $200J/mol$ and
$C_{p,m}\left(A\right)$ is $150J/mol$.
$△H_{300K}=-10KJ$
And $△H_{310K}-△H_{300K}=(3\ast 200-2\ast 300-1\ast 150)\ast △T=-1500$

$=-1.5$ kJ/mole
So for reaction enthapy change at 310K is -
$△H_{310K}=-1.5-10=-11.5$KJ/mole.