How to work out this ideal gas equation questions? (changing conditions of gas?) A l

40 cm3 of oxygen and 60 cm3 of carbon dioxide, each at 298 K and 100 kPa, were placed into an
evacuated flask of volume 0.50 dm3
. Calculate the pressure of the gas mixture in the flask at 298 K.

The answer is 20,000Pa

Im not sure what to do! We are not given the moles nor the concentration to work out the moles of the molecules. Furthermore re-arranging PV= nrt won't do anything as even when we have found the moles i'm not sure what to do next? :/

Hi
Find moles :
n = Pv /RT
= (100*1000) * ((40+60)/1,000,000) / 8.31*298
=4.038*10-3

Then put moles back into the equation to find pressure
P=nRT/v
=(4.038*10-3) * 8.31 * 298 / (0.50/1000)
= 20,000 Pa

Feel free to ask any questions if u didnt understand then it’s my fault since I didn’t explain well

Step 1: Find moles of CO2 and O2 at 298 and 100kpa. Use ideal gas law. Then sum the # of moles together

Step 2: Then use ideal gas equation again, with volume being 0.5 dm3, temp being 298 and the moles being what you just calculated.

Does that help? (don't forget to convert volume units btw)

Hi thank you so much I understand now haha! So I assume to use this method for similar questions with different volumes for different gases put into one container.

I actually got this example from a revision guide on the website. https://chemrevise.files.wordpress.com/2019/12/1.2-revision-guide-calculations-aqa.pdf
page 9. It talks about the first method like you did up there.
But then it goes on about a second method which I have never seen before in my specification nor really understand? It seems like a whole new ideal gas equation. I have copied and pasted the text below but honestly its clearer on the link

There are two approaches to solving this

1. Work out moles of gas using ideal gas equation then put back into ideal gas equation
with new conditions

2. Or combine the equation n= PV/RT as on below
(Can do this as moles of gas do not change)
P1V1 = P2V2
-------- ---------
T1 T2

As temperature is the same can make the above equation P1V1 = P2V2 P2 = P1V1 /V2 = 100000 x 1x 10-4 / 5x10-4 = 20 000 Pa

Hi I have never seen / studied that method but if it works then it’s alright to use and if itsnot in your specification then stick with the 1st method that is in your specification and especially if you do understand the method in your specification then just stick with that. It’s not in my specification either I don’t think

Cheers buddy! Yeah haha I will it's really weird Thanks again

40 cm3 of oxygen and 60 cm3 of carbon dioxide, each at 298 K and 100 kPa, were placed into an
evacuated flask of volume 0.50 dm3
. Calculate the pressure of the gas mixture in the flask at 298 K.

The answer is 20,000Pa

Im not sure what to do! We are not given the moles nor the concentration to work out the moles of the molecules. Furthermore re-arranging PV= nrt won't do anything as even when we have found the moles i'm not sure what to do next? :/