Pressure, Celsius and Volume?

Question

What partial pressure of oxygen is a scuba diver breathing if the total pressure is 6.3 atm and 20 % of the air is oxygen?

An air-filled balloon has a volume of 225 L at .94 atm and 25ºC. Soon after, the pressure changes to .99 atm and the temperature changes to 0ºC. What is the new volume of the balloon? (Hint: Create a ratio of two ideal gas equations and cancel the variables that do not change)

A gas confined in a 515 cm3 container exerts a pressure of 107.4 kPa at 38.6ºC. At what Celsius temperature will it exert a pressure of 635.6 kPa if it is placed into a 644 cm3 container?

I don't really understand how to do these equations, could someone help?

Answer 1

0.2*6.3=1.26 atm

...................................

p1*V1=n*R*T1........(1)

p2*V2=n*R*T2........(2)

Divide (1) by (2) ==>

p1*V1/(p2*V2)=T1/T2 ==>

V2=p1*V1*T2/(p2*T1)

V2=0.94*225*(273+25)/(0.99*273) liters

...................................

Similarly to the previous:

p1*V1=n*R*T1........(1)

p2*V2=n*R*T2........(2)

Divide (1) by (2) ==>

p1*V1/(p2*V2)=T1/T2 ==>

T2=p2*V2*T1/(p1*V1)

T2=635.6*644*(273+38.6)/(107.4*515) K (kelvins)

T2(in ºC)=T2(in K)-273