Thermodynamics: the study of systems involving energy in the form of heat and work.

The First Law of Thermodynamics: Q = ΔU + W

Q represents heat added to a system (or removed if it is negative)

U is the internal energy of the system (the energy associated with the motion of the atoms and/or molecules), so ΔU is the change in the internal energy. This is directly proportional to the change in temperature.

W is the work done by the system.

The First Law is often written as ΔU = Q - W