Enter the heat energy of a system and the work performed on that system to calculate the change in internal energy.

Change in Internal Energy Formula

The following formula is used to calculate the change in internal energy.

\Delta U = q + w

  • Where \Delta U is the change in internal energy (J)
  • q is the change in heat energy
  • w is the work performed on or by the system

Change in Internal Energy Definitoin

A change in internal energy is defined as the total sum of the change in heat energy and change in work performed on or by a system.

Change in Internal Energy Example

How to calculate the change in internal energy?

  1. First, determine the change in heat.

    For this example we will say the change in heat energy was 20J.

  2. Next, determine the work done on or by the system.

    For this example, we will say the system performed 10J of work on something outside the system, i.e. -10J of work done.

  3. Finally, calculate the change in internal energy.

    Using the formula we find the change in internal energy to be 20J + (-10J) = 10J.

FAQ

What is internal energy?

Internal energy is the total energy contained within a system including heat energy and potential energy.

Can you calculate internal energy?

In general, it’s only appropriate to calculate the change in internal energy of a system since it’s typically impossible to measure internal energy directly.