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 $A+2B\to 3C$ at $300K$ is $-10kJ/mol\&C_{p,m}\left(2\right)$ is $300Jmo{l}^{-1}$ then enthalpy change at $310K$ is

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

Answer 1

Answer: (C)

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