Question

A balloon vendor at a street fair is using a tank of helium to fill her balloons. The tank has a volume of 155.0 L and a pressure of 126.0 atm at 23.0 °C. After a while she notices that the valve has not been closed properly. The pressure had dropped to 116.0 atm (The tank is still at 23.0 °C). How many moles has she lost?

Answer 1

we have:

P = 126.0 atm

V = 155.0 L

T = 23.0 oC

= (23.0+273) K

= 296 K

find number of moles using:

P * V = n*R*T

126 atm * 155 L = n * 0.08206 atm.L/mol.K * 296 K

n = 804 mol

This is initial number of moles of gas in tank

we have:

n1 = 804 mol

P1 = 126.0 atm

P2 = 116 atm

we have below equation to be used:

P1/n1 = P2/n2

126.0 atm / 804 mol = 116.0 atm / n2

n2 = 740 mol

this is final number of moles of gas

gas escaped = initial - final

= 804 mol - 740 mol

= 64 mol

Answer: 64 mol