Question

For an open unsteady state system, 15 J of heat was taken off and 10 J of work was done by the system, what is the value of a change in enthalpy?

(a) – 5 J

(b) 5 J

(c) 25 J

(d) – 25 J

The question was asked by my school teacher while I was bunking the class.

This intriguing question comes from Vaporization and Energy Balances for Open, Unsteady-State Systems in chapter Introduction to Energy Balances for Processes without Reaction and Calculation of Enthalpy Changes of Basic Chemical Engineering

Answer 1

Right option is (a) – 5 J

Easiest explanation: ∆H = 10 – 15 = – 5 J.