Answer to Question #336333 in General Chemistry for jay

Question

What is the change in internal energy (in J) of a system that absorbs 0.521 kJ of heat from its surroundings and has 0.597 kcal of work done on it? Give your answer in scientific notation.

Answer 1

The first law of thermodynamics relates the work and the transferred heat exchanged in a system through internal energy. This energy is neither created nor destroyed, it is only transformed.

Taking into account that the internal energy is the sum of all the energies of the particles that the system has, you have:

ΔU = Q + W

where U is the internal energy of the system (isolated), Q is the amount of heat contributed to the system and W is the work done by the system.

By convention, Q is positive if it goes from the environment to the system, or negative otherwise, and W is positive if it is carried out on the system and negative if it is carried out by the system.

In this case:

Q = 0.521 kJ (because the energy is absorbed, this is,it goes from the environment to the system)

W = 0.597 kcal = 2.499 kJ (because the work is done on the system, and being 1 kcal = 4.184 kJ)

Replacing:

ΔU = 0.521 kJ + 2.499 kJ = 3.02 kJ