Which equation relates internal energy, heat, and work?

The equation that relates internal energy, heat, and work is ∆U = Q + W. This equation is derived from the first law of thermodynamics, which states that the change in internal energy of a system (∆U) is equal to the heat added to the system (Q) plus the work done on the system (W).

In this context, Q represents the thermal energy transfer into or out of the system, while W signifies the mechanical work done on or by the system. If heat is added to the system, Q is positive, contributing to an increase in internal energy. Likewise, if work is done on the system, W is also positive, leading to an increase in internal energy. Conversely, if heat is lost from the system or work is done by the system, these values would be negative, resulting in a decrease in internal energy.

This fundamental relation is critical in both thermodynamics and physical chemistry as it provides a clear understanding of how energy is conserved and transformed within a system.