# In a chemical reaction you collect 1L Hydrogen gas at STP. How many moles of hydrogen gas did you collect?

Mar 13, 2018

$\text{0.0446 mol}$.

#### Explanation:

In this question, we're given:

• $p$, or pressure, of $\text{1 atm}$. We know this because it tells us that we're at STP.
• $V$, or volume, of $\text{1 L}$.
• $T$, or temperature, at $\text{273.15 K}$. We know this because it tells us that we're at STP.

We need to find $n$, or number of moles.
The Ideal Gas Equation relates all of these variables!:

$p V = n R T$

We can rearrange this to only have $n$ on one side:

$n = \frac{p V}{R T}$

We know the value of $R$, or the Universal Gas Constant, to be $\text{0.08206 L atm/K mol}$ because the units for our given values are in $\text{L}$, $\text{atm}$, and $\text{K}$.
Now, we can just plug in the variables and solve:

$n = \left(\text{1 atm" xx "1 L")/("0.08206 L atm/K mol" xx "273.15 K}\right)$
$n = \left(1 \cancel{\text{atm") xx 1 cancel("L"))/(0.08206 cancel("L") cancel("atm")"/"cancel("K") "mol" xx 273.15 cancel("K}}\right)$
$n = \text{0.0446 mol}$

We can verify that our answer is correct by plugging everything into the Ideal Gas Equation again and seeing if $p V$ is really equal to $n R T$:

$p V = n R T$
$\text{1 atm" xx "1 L" = "0.0446 mol" xx "0.08206 L atm/K mol" xx "273.15 K}$
$1 = 1$

Yay! :)