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bog standard a2 gas law question calculate the pressure...

A sealed can of fixed volume contains air at a pressure 101kpa at 100c. The can is then cooled to a temperature of 20c. calculate the pressure of the air in the can.

I thought this was just p1/t1 = p2/t2

so rearrange to : (p1t2)/ t1 = P2

but this isnt working for me :frown:

answer should be 79kpa

Reply 1

Who_Is_It?

Did you remember to convert your temperature in degrees Celsius to kelvin??
That may be the problem :smile:

Reply 2

2cool

Original post by Who_Is_It?

Did you remember to convert your temperature in degrees Celsius to kelvin??
That may be the problem :smile:

nope ! will try that now and edit this post in a minute :smile:

damn that was dumb!

edit: thank you ! but im immediately stuck on this now:

A hand pump of volume 2.0x10^-4 is used to force air through a valve into a container of volume 8x10^-4 which contains air at initial pressure of 101kpa. calculate the pressure of the air in the container after one stroke of the pump, assuming temperature is unchanged....

im confused with what to do for this as the volume of the container cant change :s-smilie:

(edited 11 years ago)

Reply 3

Who_Is_It?

Original post by 2cool

nope ! will try that now and edit this post in a minute :smile:

I remember doing something like this before. You're just using Boyles law which is pV=constant

Initially the pump and container are connected so the total initial volume would be (2.0x10^-4 + 8x10^-4)
When you compress the pump the total volume in the pump would become zero (because its completely pressed in) but the volume of the container remains at 8x10^-4. So final volume becomes 8x10^-4.

Because the volume is decreasing the pressure is increasing. This is because the amount of gas in the system stays the same but its just confined to a smaller space/volume if you know what I mean :tongue: