# A balloon has a volume of 1.0L at 21.0 degrees C and 750 mmHg. What is the balloon's volume at STP ?

Aug 18, 2016

We need first to define conditions of $\text{STP}$.

#### Explanation:

$\text{Standard temperature and pressure}$ specifies $273.15 \cdot K$ and $100 \cdot k P a$ $=$ $\text{1 bar}$

Now $\text{1 bar}$ $\equiv$ $\text{750 mm Hg}$

Thus $\frac{{\cancel{P}}_{1} {V}_{1}}{T} _ 1$ $=$ $\frac{{\cancel{P}}_{2} {V}_{2}}{T} _ 2$

${V}_{2}$ $=$ ${V}_{1} / {T}_{1} \times {T}_{2}$ $=$ $1.0 \cdot L \times \frac{294.15 \cdot K}{273.15 \cdot K}$ $=$ $\text{a bit over 1 litre}$.

The volume increase makes sense as we increase the temperature, we should increase the volume of a fixed quantity of gas.