Internal energy is the sum of a random distribution of kinetic and potential energies associated with the molecules of a system. It is determined by the state of the system and is a function of temperature, pressure, and volume.
A rise in temperature of an object is related to an increase in its internal energy. When heat is added to a system, its internal energy increases.
The work done when the volume of a gas changes at constant pressure is given by W = p∆V, where p is the pressure and ΔV is the change in volume. The work done by the gas is positive, while the work done on the gas is negative.
The first law of thermodynamics states that the change in internal energy (∆U) of a system is equal to the heat added to the system (q) plus the work done on the system (W), expressed as ∆U = q + W.
The first law of thermodynamics is a statement of the conservation of energy. It states that energy cannot be created or destroyed, only transferred or converted from one form to another.
The sign convention for work and heat is important in the first law of thermodynamics. Work done on the system is negative and work done by the system is positive. Heat added to the system is positive, while heat removed from the system is negative.