# If I have 72 liters of gas held at a pressure of 3.4 atm and a temperature of 225K How many moles of gas do I have?

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Here again we have to assume that that the gas is behaving as an ideal gas. Then we can apply the ideal gas law to calculate the number of gas molecules in this question.

The ideal gas law can be expressed as,

`PV = nRT`

since it is required to find out the number of gas moles we can rearrange the equation as follows,

`n = (PV)/(RT)`

here,

P =3.4 atm

V =72 lit

T= 225K

R = 0.082057 lit.atm/(K.mol)

Then,

`n = (PV)/(RT)`

`n = ((3.4 atm)(72 lit))/((0.082057 (lit.atm)/(K.mol))(225K))`

n = 13.26 mol

**Therefore the number of gas moles is 13.26 mol**