a gas occupied 500.0L when it was collected over water at a pressure of 750mmHg and a temperature of 21 C. calculate the volume of dry gas at 730mmHg and 5 C.

It would be a very big help if someone can help me answer this. Please and thank you!

Question

a gas occupied 500.0L when it was collected over water at a pressure of 750mmHg and a temperature of 21 C. calculate the volume of dry gas at 730mmHg and 5 C.

It would be a very big help if someone can help me answer this. Please and thank you!

aaronq · Answer

you only need to apply the ideal gas law, PV=nRT. You're comparing two conditions of the same system, so you can move all the terms to one side, $\dfrac{PV}{nRT}=C$ and make it equal to the other system.

so it's $\underbrace{\dfrac{P_1V_1}{nRT_1}}=\underbrace{\dfrac{P_2V_2}{nRT_2}}$

    conditions 1   conditions 2

since since it's a closed system, n is constant (R is always constant so we can drop them.

the formula is reduced to: $\dfrac{P_1V_1}{T_1}=\dfrac{P_2V_2}{T_2}$

anonymous · Answer

Okay. and we are looking for V2 correct? I've just been very very confused with this question. I appreciate you helping me!

aaronq · Answer

no problem ! and yes you're looking for the new volume, $V_2$. So convert the temp to the Kelvin scale, plug in your values, then solve (algebraically) for the new V.

anonymous · Answer

okay, this is what I did. V2=(T2)(P1)(V1)/(T1)(P2)

anonymous · Answer

V2= (278K)(750mmHg)(500.0L)/(294K)(730mmHg)

anonymous · Answer

V2= 258852040.82 but something seems weird. this answer is too large lol

aaronq · Answer

i got 485.7422421023203802

aaronq · Answer

you messed up somewhere plugging into your calculator

anonymous · Answer

hahahaha!!! I'm sure I did!!!

aaronq · Answer

haha you should do it in steps, first do the top multiplication, the bottom multiplication, then the top and the bottom division.

anonymous · Answer

oh okay! yes I got the same answer now!

anonymous · Answer

I have my answer in least number of sig figs, so would the final answer be 485.7?

anonymous · Answer

I have to have my answer in*

aaronq · Answer

hm so is the least number of sig figs 1, because 5 Celsius?

aaronq · Answer

or are we using the sig figs of the volume 500.0 L?

anonymous · Answer

well since I had to change the temperatures to kelvin... I think it would be 2 because 500.0 is 4, the temperatures are both 3, and both 750mmHg & 730mmHg are 2 sig figs

anonymous · Answer

Oh I see what you are saying, going by the least number of decimal points.

aaronq · Answer

hmm i would try 486 first

anonymous · Answer

I'll put 486 as my final answer. Thank you so much for all of your help! I really appreciate it!!!!

aaronq · Answer

no problem !