# The temperature of a fixed mass of an ideal gas goes from 40ºC to 80ºC at a constant volume. If the initial pressure was x, what is the new pressure?

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The mark scheme says it's 2x, but do we use ºC or K in the equation P1/T1 = P2/T2?

The mark scheme says it's 2x, but do we use ºC or K in the equation P1/T1 = P2/T2?

##### 1 Answer

Dec 21, 2017

Celsius.

#### Explanation:

Given:

#P_1=x# #T_1=40^oC=313K# #T_2=80^oC=353K#

We can see that the temperature is *not* the same ratio in Kelvin as Celsius, as while 40 is half of 80, 313 is not half of 353.

With Kelvin:

#P_1/T_1=P_2/T_2#

#=>P_2=(P_1T_2)/(T_1)#

#=>P_2=x*353/313#

With Celsius:

#P_1/T_1=P_2/T_2#

#=>P_2=(P_1T_2)/(T_1)#

#=>P_2=x*80/40#

#=>P_2=2x#

So it appears they wanted you to use Celsius.