Question

What is the final enthalpy of the solution made by mixing 100 grams of 10% NaOH having enthalpy 40 J with 300 grams of 90% NaOH having enthalpy 20 J?

(a) 10 J

(b) 15 J

(c) 25 J

(d) 40 J

This question was posed to me in class test.

Query is from Effects of Mixing into Energy Balance in division Energy Balances that Include the Effects of Chemical Reaction, Ideal Processes, Efficiency and the Mechanical Energy Balance and Heats of Solution and Mixing of Basic Chemical Engineering

Answer 1

Correct answer is (c) 25 J

The explanation is: Final enthalpy = 0.25*40 + 0.75*20 = 10 + 15 = 25 J.