Question

In a particular reaction, $1.5kJ$ of heat released from the system and $4.5kJ$ of work is done on the system. What are the changes in:
(i) Internal energy
(ii) Enthalpy of the system?

Answer 1

Given that the heat is released from the system and the work is done on the system.

Therefore,

$q=-1.5kJ$

$w=4.5kJ$

Now from first law of thermodynamics,

(i) $\Delta U=q+w$

$\Rightarrow \Delta U=-1.5+4.5=3kJ$

Hence the change in internal energy of the system is $3kJ$.

(ii) Now as we know that, enthalpy of the system is given as-

$\Delta H=\Delta U+w$

$\Rightarrow \Delta H=3+4.5=7.5J$

Hence the enthalpy of the system is $7.5J$.