# Homework Help: PV=nRT Need help asap

1. Apr 27, 2012

### cuddlylover

PV=nRT Need help asap :)

An ideal gas has an initial volume of 500 cm3, an initial temperature of 20C, and an initial
pressure of 2 atm. What is its nal pressure if the volume is allowed to expand to 1000 cm3
while the temperature increases to 60C?

Im trying to work this out i have got it to 2atm.500cm3/293k = p2.1000cm3/333k but cant work out how to get p2.

If someone could point me the right way would be a big help.

2. Apr 27, 2012

Re: PV=nRT Need help asap :)

Hello cuddlylover

First off, I'd strongly recommened that getting into the habbit converting all figures into base units. This makes things easier for much tougher problem solving questions so:

Convert 2atm would = 2(101325)pa

anyway...

Lets look the forumla:

I think the forumla you're using is incorrect, in the title, you are using the ideal gas equation. whereas, I think you need the combined gas law which is:
$\frac{PV}{T}$ = k
or
$\frac{PV}{T}$=$\frac{PV}{T}$

If you wanted to find P on the right hand side, take T then V to the other side ;)

3. Apr 27, 2012

### cuddlylover

Re: PV=nRT Need help asap :)

Thanks for that. You where right i was using the combined gas law.

"If you wanted to find P on the right hand side, take T then V to the other side ;)"

Sorry im a comp sci major being made to do this :)

4. Apr 27, 2012

Re: PV=nRT Need help asap :)

No worries, we all have our strengths are weaknesses :P

... finish this sentence...

because the T on the right hand side is divided by, on the left and side it will be...

and this one

because the V is being multiplied by on the right hand side, on the left it will be...

Now take the T and the V to the left hand side of the equation

5. Apr 27, 2012

### RoshanBBQ

Re: PV=nRT Need help asap :)

Since when does a computer science major claim he is unable to do high school chemistry due to his major?
$$pv=nrt$$
n and r are constants. We see then that
$$\frac{pv}{t} = nr$$
This means
$$\frac{p_1v_1}{t_1} = \frac{p_2v_2}{t_2}$$
I am pretty sure he is not having problems doing algebra...

The formula is not incorrect. Calling upon an arbitrary manipulation of gas law and renaming it "combined gas law" is just plain confusing. You should just show him the common sense manipulation of gas law.

6. Apr 27, 2012

### cuddlylover

Re: PV=nRT Need help asap :)

Still not getting it so if i have p1.v1/t1 = p2.v2/t2 i can just more them over to make p1.v2/t2 and that will give me p1?

7. Apr 27, 2012

### RoshanBBQ

Re: PV=nRT Need help asap :)

I'm not sure the answer can be any clearer. Just remember to watch your units.