Question

A chemical reaction is carried out by supplying 8 kJ of heat. The system performs the work of 2.7 kJ. Calculate ΔH and ΔU.

Answer 1

Given :

Q = + 8 kJ 

(since heat is absorbed by the system) 

W = -2.7 kJ 

(It will be a work of expansion) 

ΔH = ?, 

ΔU = ? 

ΔU = Q + W 

= 8 + (-2.7) 

= 5.3 kJ 

Internal energy of the system will increase by 5.3 kJ.

Due to expansion, 

ΔV > 0,

ΔH = ΔU + PΔV 

= 5.3 + 2.7 

= 8 kJ 

Enthalpy of the system will increase by 8 kJ

∴ ΔU = 5.3 kJ, ΔH = 8 kJ