Question

Calculate the work done in the following reaction at 50°C. State whether work is done on the system or by the system.
${\displaystyle {\text{SO}}_2\left(\text{g}\right)+\frac{1}{2}{\text{O}}_{2\left(\text{g}\right)}\to {\text{SO}}_{3\left(\text{g}\right)}}$

Answer 1

${\displaystyle {\text{SO}}_2\left(\text{g}\right)+\frac{1}{2}{\text{O}}_{2\left(\text{g}\right)}\to {\text{SO}}_{3\left(\text{g}\right)}}$
Δn =  (moles of gaseous product) -  (moles of gaseous reactant)
= 1-(1+${\displaystyle \frac{1}{2}}$)
=${\displaystyle -\frac{1}{2}}$
w = - ΔnRT
-( ${\displaystyle -\frac{1}{2}\times 8.314\times 323}$)
=1342.7J
As work done is positive. Therefore work is done by surrounding on system.

(OR)

The standard enthalpy of combustion of formaldehyde Δ ₀H⁰ = -571 kJ How much heat will be evolved in the formation of 22 g of CO₂ ?