# Pressure-temperature question

Hello guys!

Can someone explain me the answer of that question ?

1 litre of oxygen has temperature of 0 Celsius. What happens to the volume if the temperature is raised to 275 Celsius, keeping the pressure constant?

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cronxeh
Gold Member
Well if you use ideal gas law P*V=n*R*T, Keep in mind that the are same number of moles so n is constant, R is constant, thus P*V = constant = Temperature

Same applies for same instance when temperature is raised to 275 deg C: Pressure2*Volume2 = constant = Temperature2

So with some rearranging, P1*V1/T1 = n*R = P2*V2/T2, keeping pressure constant (0 C = 273 Kelvin, 275 C = 548 Kelvin) :

V1/T1 = V2/T2

V2 = V1*T2/T1 = 1 Liter*548/273 = 2 Liters

The volume doubles

First thank you very much for the quick reply but I couldn't understand what you mean by :

Same applies for same instance when temperature is raised to 275 deg C: Pressure2*Volume2 = constant = Temperature2

why you do " pressure2* " , it means "to square" ?

cronxeh
Gold Member
First thank you very much for the quick reply but I couldn't understand what you mean by :

Same applies for same instance when temperature is raised to 275 deg C: Pressure2*Volume2 = constant = Temperature2
Increasing the temperature does not change the number of moles or the ideal gas constant R. You simple have all these little gas balls bouncing around the container they are enclosed in increasing the pressure when you increase temperature. The higher the temperature the more bouncing is going on, generally speaking. So you can assume these things are constant. Pressure*Volume when temperature is 0 deg C is one instance and when temperature is 275 deg C it is (Pressure #2) * (Volume #2) that is constant

why you do " pressure2* " , it means "to square" ?
No Pressure2 means Pressure when the temperature is 275 deg C. It is a different pressure than when the temperature is 0 deg C. However for this problem this is not even important because pressure is constant (Meaning Pressure1 = Pressure2), so you can just simplify the ideal gas law to Charles Law. I would rather learn how to think critically than learn 3 different laws. Instead you just learn the Ideal Gas Law and how to apply it.

And for future reference pressure squared is written as pressure^2

Oh ok * now it's all clear!

And also 1 small thing : why did you convert the temperature to Kelvin instead of solving by Celsius? Is it a rule?

Because it's the point that I couldn't solve the problem.