# A balloon inﬂated at 250 K has a volume of 4.0 L. What is the new volume at constant pressure if the temperature changes to 500 K?

Charles' law states that at constant pressure, absolute temperature and volume are proportional. Mathematically, $V$ $\propto$ $T$. $T$, the temperature, is quoted in Kelvins.
Given the proportionality, ${V}_{1} / {T}_{1}$ $=$ ${V}_{2} / {T}_{2}$. ${V}_{2}$ is unknown, but ${V}_{2}$ $=$ $\frac{{T}_{2} \times {V}_{1}}{T} _ 1$