# A balloon with a volume of 2.00L is filled with helium gas at a temperature of 27.0˚C and a pressure of 1.20 atm. How many grams of helium are in the balloon?

May 28, 2017

A mass of approx. $0.4 \cdot g$ is contained........

#### Explanation:

Given $n = \text{Mass"/"Molar mass} = \frac{P V}{R T}$.

$\text{Mass"=(PV)/(RT)xx"molar mass}$,

.........Agreed........?

And, as is typical, we use the value of..........

$R = 0.0821 \cdot L \cdot a t m \cdot {K}^{-} 1 \cdot m o {l}^{-} 1$

The which has units that chemists typically use. And so we plugs in the numbers:

$\text{Mass} = \frac{1.2 \cdot a t m \times 2.00 \cdot L \times 4.00 \cdot g \cdot m o {l}^{-} 1}{0.0821 \cdot \frac{L \cdot a t m}{K \cdot m o l} \times 300 \cdot K}$

$\cong 400 \cdot m g$