Please help for my Chemistry class

Question

An ideal gas occupying a 2.0 L flask at 760 torr is allowed to expand to a volume of 6L. Calculate the final pressure in atm.

 

A gas occupies a volume of 400 mL at a pressure of 3.3 atm. At what pressure would its volume be 42 mL?

Answer 1

Hello, Josefa,

Use the gas law relationship P1V1/T1 = P2V2/T2, where 1 and 2 represent the initial and final states. Temperature must always be in K. Rearrange the equation to isolate the unknown. and then plug in the other values.

The first question ask for P2, the final pressure.

P2 = P1(V1/V2)(T2/T1)

Note that I rearranged the values of volume and temperature as ratios, in order to help us understand what is happening. No temperatures are given,so we can assume the temperature is constant. (T2/T1) simply reduces to 1, regardless of the actual temperature.

P2 = P1(V1/V2)(T2/T1)

We can see that since the volume increases in the problem, that P2 will decrease, since (V1/V2) is less than 1.

P2 = 760 torr*(2L/8L)

P2 = 250.3 torr

They want the answer in atm, so

(253.2 torr)*(1 atm/760torr) = 0.333 atm

The second problem is done the same way. The unknown in this case is P2.

P2 = P1(V1/V2)(T2/T1)

The temperature is assumed to be constant.

P2 = P1(V1/V2)

P2 = 3.3atm*(400 ml/42 ml)

P2 = 31.4 atm

Bob