Question

What is the new volume of a balloon originally at 755 torr and 5.00 l is placed in a container in which the pressure is increased to 1.25 atm?

Answer 1

Answer is: volume will be 3.97 liters.

Boyle's Law: the pressure volume law -  volume of a given amount of gas held  varies inversely with the applied pressure when the temperature and mass are constant.

p₁V₁ = p₂V₂.

p₁ = 755 torr.

V₁ = 5.00 l.

p₂ = 1.25 atm · 760 torr/atm.

p₂ = 950 torr.

755 torr · 5 l = 950 torr · V₂.

V₂ = 755 torr · 5 l / 950 torr.

V₂ =  3.97 l.

When pressure goes up, volume goes down.

When volume goes up, pressure goes down.

Answer 2

Boyle's law states that pressure is inversely proportional to volume at constant temperature 
PV = k
where P - pressure , V -volume and k - constant 
P1V1 = P2V2
where parameters for the first instance are on the left side and parameters for the second instance are on the right side of the equation 
P1 - 755 torr x 0.00131 atm/torr  = 0.989 atm
substituting the values in the equation 
0.989 atm x 5.00 L = 1.25 atm x V 
V = 3.96 L
new volume is 3.96 L