[arinarinarin]

Hey guys...i have a question in chemistry with probably many more to come....

Guys...how do I do this question...

A 798 ml sample of gas is collected at 5.00C, 621 mmHG. What is the volume at STP....Thanks

I am not sure which law I should use...

[Borek]

pV = nRT

or

p₁V₁/T₁ = p₂V₂/T₂

[arinarinarin]

thanks a loott...what would the n be in for the eqaution...how do i found out the number of moles..


i know 1 mol =22.4 L

EDIT: Is the answer 6.4?

[Borek]

what would the n be in for the eqaution

number of moles, R is universal gas constant

how do i found out the number of moles

solve for n?

Is the answer 6.4?

Without checking - no. You started collecting gas close to the STP (621 mmHg vs 760 mmHg and 5 deg C vs 0 deg C - or rather 278K vs 273K) so the change in the voulme will be not that large.

Although digits 6 and 4 suggest that you are on the right track. Check your units.

[arinarinarin]

ok...this is very perplexing....i got 640 using the combined gas law..

[arinarinarin]

how would the eqation be set up..


621x=1x278x?

[Borek]

how would the eqation be set up..


621x=1x278x?

Do you use x for unknown and for multiplication at the same time?

p₁V₁/T₁ = p₂V₂/T₂

so if V₂ is the volume you are looking for:

621 mmHg * 798 mL / 278 K = 760 mmHg * V₂ mL / 273 K

Note that as long as you use same units on both sides it doesn't matter what units are used as they cancel out.

[arinarinarin]

using your eqaution...i got 640ml...does that sound right?

[arinarinarin]

do u have aim...or any messenge program.....mine mine is "dummehead"...im me if possible...thasnk a lot for having patients in me..

[Borek]

using your eqaution...i got 640ml...does that sound right?

Exactly 

[arinarinarin]

so its righttttttttttt.....YEEEYYY i feel smart

[Borek]

do u have aim...or any messenge program

No, but even if I don't plan to use it on forums - other may learn something too from our discussion.

[arinarinarin]

oh ok...thast sounds far...i ahve many queestions too...but i fel like I have already taken enough of you time....I;m in tenth grade and I have a final tomorrow...our teahcer is like th e worst chemistry teacher that does not teach us anything...we aslo ahve theose tenth grads who think they are cool that distrupt the whole class...anyways...thanks a lot ofr your help.

[Donaldson Tan]

We all love to help you.

The ideal gas law states that PV = nRT where
P: Pressure
V: Volume
n: number of moles (amount)
R: Universal Gas Constant
T: Absolute Temperature

In the process of changing the pressure and temperature of the gas, its mass remains constant. This means n is constant.

PV = nRT
PV/T = nR = constant

Hence, P₁V₁/T₁ = P₂V₂/T₂

You can use this equation to evaluate the volume of the gas at STP.