# How many moles of hydrogen are there in 1.5 L balloon at STP? (r = 0.0821 L*atm*K^-1*mol^-1)

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justaguide | Certified Educator

The volume (V) of ideal gases is related to the temperature (T) of the gas and the pressure (P) in which it is placed by the formula: P*V = n*R*T where n is the number of moles and R is a constant equal to 0.0821 L*atm*K^-1*mol^-1.

STP or standard temperature and pressure is defined by IUPAC as a condition where the temperature is 273.15 K and pressure is 0.986 atm.

Taking hydrogen as an ideal gas and substituting these values in the formula given earlier:

1.5*0.986 = n*0.0821*273.15

=> n = (1.5*0.986)/(0.0821*273.15)

=> n = 0.0659

There are 0.0659 moles of hydrogen in a 1.5 L balloon at STP.