Question

The molar heat capacities at constant pressure (assume constant with respect to temperature) of $A,B$ and $C$ are in ratio of $1.5:3.0:2.0$ . If enthalpy change for the exothermic reaction $A+2B \rightarrow 3C$ at $300K$ is $-10kJ/mol\&C_{p , m}\left(2\right)$ is $300Jmol^{- 1}$ then enthalpy change at $310K$ is

• A. $-8.5kJmol^{- 1}$
• B. $8.5kJmol^{- 1}$
• C. $-11.5kJmol^{- 1}$
• D. none of these

Answer 1

Answer: (C)

Using $\triangle H=nC_{p}​\triangle T$
$C_{p},m​\left(\right.B\left.\right)=300J/mol$
So by the ratio $1.5::3.0::2.0$ we get
$C_{p},m​\left(\right.C\left.\right)=200J/mol$ and $C_{p},m​\left(\right.A\left.\right)=150J/mol$
Now
$\triangle H_{300 K}​=-10KJ$
Also
$\triangle H310K​-\triangle H_{300 K}=\left(\right.3\times 200-2\times 300-1\times 150\left.\right)\times \triangle T=-1500=-1.5kJ/mole$
So for reaction enthalpy change at $310K$ :
$\triangle H_{310 K}​=-1.5-10=-11.5KJ/mole.$