[Frith 08]

I am having trouble with this particular question:

A fixed mass of gas has a volume of 750 ml at -23ºc and 800mm pressure. Calculate the pressure which at which it will have a volume of 720ml at -3ºc. Leave answer in fraction.

p1= 800 mm p2= ?

V1= 750 ml  v2= 720 ml

T1= -23ºc   T2= -3ºc

800X750  =    P2X720 
   -23ºc            -3ºc          
Then I'm stuck here. Can you please help me with this calculation.

Thank you

[sameeralord]

Great to see you have attempted the question. Good work 

800X750  =    P2X720
   -23ºc                       -3ºc   

So you are using the formula

pv=nrt

r=pv/nt

Since r is a constant the ratios should always equal

p1v1/n1t1 = p2v2/ n2v2

As same mass moles are the same and they cancel out.

So what you have done is right except some mistakes with the units I think. Volume in Litres and temp should be in Kelvins. Pressure in kilo pascals

101.325 : 760
 X         : 800

Work out X and use that for pressure. Add 273 to temp to get the temp in Kelvins. Example (273 -23 ). Convert ml to L

Then work out P2 using basic transposing.