Question

A science class puts a balloon containing 1.25 l of air at 101 kpa into a bell jar. using an air pump, the class removes some of the air in the jar, causing the balloon to expand to a volume of 2.25 l. assuming a constant temperature, what is the new pressure inside the jar?

Answer 1

The first thing you should know in this case is the following definition:
PV = nRT
Then, as the temperature is constant, then:
PV = k
Then, we have two states:
P1V1 = k
P2V2 = k
We can then equalize both equations:
P1V1 = P2V2
Substituting the values:
(1.25) * (101) = (2.25) * (P2)
Clearing P2:
P2 = ((1.25) * (101)) /(2.25)=56.11Kpa
answer:
the new pressure inside the jar is 56.11Kpa