Question

The internal energy change in a system that has absorbed 2 Kcal of heat and done 500 J of work is:

• A. 7900 J
• B. 8900 J
• C. 3400 J
• D. 5400 J

Answer 1

The correct option is A 7900 J

The First Law of Thermodynamics states that energy can be converted from one form to another with the interaction of heat, work and internal energy, but it cannot be created nor destroyed, under any circumstances. Mathematically, this is represented as

$\Delta H=\Delta U+\Delta nRT$

where,

$\Delta H$ is the heat exchanged between a system and its surroundings,

$\Delta U$ is the total change in internal energy of a system,

$\Delta nRT$ is the work done by or on the system.

Given,

$\Delta H=2Kcal=8400JW=500JSo,\Delta U=8400-500=7900J$.

Hence,option A is correct.