The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic systems.

First Law of Thermodynamics for a closed system undergoing a process neglecting kinetic and potential energy.

δQ = dU + δW

The heat added to the system has been considered to be a positive quantity.

Conversely, if heat were removed, then the heat would be a negative quantity.

Work done  on the system = sign convention is -ve

Work done by the system = sign convention is +ve

Note that if no heat transfer occurs, the system is called adiabatic.

Work is also subject to a sign convention, which is work done by a system is positive work done on a system is negative

Heat or energy transfer to the system = sign convention is +ve

Heat or energy transfer from the system = sign convention is -ve

Point functions:

• Point functions are defined as the thermodynamic variable which depends on end states only i.e. initial and final states. They do not depend upon the path followed.
• The differential of point functions is exact.
• Pressure, temperature, volume, entropy, enthalpy, etc are point functions.

Path functions:

• Path functions are defined as the thermodynamical variables which depend on the way/path in which the thermodynamical system achieved the initial and final states.
• The differential of path functions is inexact.
• Heat, Energy transfer, work and entropy generation are path functions.