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.

= q + w

- Where 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?

**First, determine the change in heat.**For this example we will say the change in heat energy was 20J.

**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.

**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 an internal energy directly.