Chemistry Homework

Question

A gas sample contains 1.44 moles at 21° C exerts a pressure of 300. torr. Some gas is 

added to the same container and the temperature is increased by 40° C. If the pressure increases 

to 750 torr, how many moles of gas were added to the container? Assume a constant- volume container.

Answer 1

Using a modification of the ideal gas law, we can obtain a modification of the combined gas law such that

P1V1/T1n1 = P2V2/T2n2

Since the volume is constant, we obtain

P1/T1n1 = P2/T2n2

P1 = 300 torr

T1 = 21ºC + 273 = 294K

n1 = 1.44 moles

P2 = 750 torr

T2 = 40ºC + 21ºC = 61ºC + 273 = 334K

n2 = ?

Solving:

(300 torr)/(294K)(1.44 moles) = (750 torr)/(334K)(n2)

n2 = (294)(1.44)(750)/(300)(334) = 3.17 moles

Moles added = 3.17 moles - 1.44 moles = 1.73 moles