Finding Pressure (in atm) when volume is reduced

Question

A gas at 379 K occupies 6.16 L at a pressure of 0.510 atm. What will its pressure (in atm) be at 250. K if its volume is reduced to 4.50 L? 

Answer 1

Need to use the combined gas law:

P₁ x V₁ P₂ x V₂

_{------------ = ---------------} substituting gives

T₁ T₂

0.51 x 6.16 P₂ x 4.50

--------------- = -------------- and rearranging gives

379 250

P₂ = 0.51 x 6.16 x 250

----------------------- = 0.461 atm

379 x 4.50

Answer 2

The Ideal Gas Law of PV = nRT is changed by dividing both sides by T. Then since n, the number of moles and R, the gas law constant, do not change the expression PV/T is a constant. Thus use the abbreviate Ideal Gas Law relationship of PV/T = PV/T.

Substituting in 0.510 * 6.16 / 379 = P * 4.5 / 250.

Solving for P: 0.510 * 6.16 * 250 / 379 * 4.5 = P = 0.461 atm.