# How many hydrogen molecules are in 2.75 L of H_2 gas at STP?

Jun 27, 2016

$\frac{2.75 \cdot L}{22.4 \cdot L \cdot m o {l}^{-} 1} \times 6.022 \times {10}^{23} {\text{ hydrogen molecules mol}}^{-} 1$ $=$ ??"hydrogen molecules"
The molar volume of an ideal gas at $\text{STP}$ is $22.4 \cdot L$.
We assume (reasonably) that dihydrogen behaves ideally, and mulitply the quotient of volumes by $\text{Avogadro's number, } {N}_{A} , 6.022 \times {10}^{23} \cdot m o {l}^{-} 1$ to give an answer in numbers of hydrogen molecules.