First Law Budget - Heat & Thermodynamics Step by Step

The first law tracks where transferred energy goes in a process.

highlighted = computed this step

Start with a heat input

A process receives 20 joules of heat. Some energy leaves as work and the rest stays as internal energy.

Q_{\text{in}} = 20\ \text{J}

The process does 12 joules of work and stores 8 joules as internal energy.

Q_{\text{in}} = W + \Delta U

Adding 12 joules and 8 joules gives the original 20 joules.

Q_{\text{in}} = 12\ \text{J} + 8\ \text{J} = 20\ \text{J}