Charles' Law - Heat & Thermodynamics Step by Step

At fixed pressure, volume is proportional to absolute kelvin temperature. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Use absolute kelvin

At fixed pressure, compare volume to absolute temperature. The first state is 6 cubic meters at 300 kelvin.

\frac{V_i}{T_i} = \frac{6\ \text{m}^{3}}{300\ \text{K}}

Raise kelvin temperature

The second state is 8 cubic meters at 400 kelvin.

\frac{V_f}{T_f} = \frac{8\ \text{m}^{3}}{400\ \text{K}}

The ratio stays constant

Both ratios equal one fiftieth cubic meter per kelvin.

\frac{V}{T} = \tfrac{1}{50}\ \text{m}^{3}/\text{K}

Volume follows absolute kelvin

The diagram draws the last two rows. At fixed pressure, doubling absolute kelvin doubles volume in this ideal-gas comparison.

\begin{array}{c|c|c}V&T&V/T\\3\ \text{m}^{3}&150\ \text{K}&\tfrac{1}{50}\ \text{m}^{3}/\text{K}\\6\ \text{m}^{3}&300\ \text{K}&\tfrac{1}{50}\ \text{m}^{3}/\text{K}\\8\ \text{m}^{3}&400\ \text{K}&\tfrac{1}{50}\ \text{m}^{3}/\text{K}\\\end{array}