Not sure how to go about working this gas law problem.

Not sure how to go about working this problem.

A 550 ml volume of hydrogen chlorine gas, HCl, is collected at 27C and 790 mmHg.
What volume would it occupy at STP?

Not sure if it is a PV = nRT or V2P2T1 = T2P1V1 problem.

It is a PV= nRT problem

First you convert mmHg to atm

790(1/760) = 1.04 atm

Then plug everything into the equation

n = PV/RT = (1.04*.550) / (.08206*300) = .023 moles HCl

then change the pressure and temperture to STP and solve

V = nRT/P = (.023*.08206*273) / (1) = 0.515 L of HCl or 515 mL of HCl

You can use P1V1/T1 = P2V2/T2 or the fact that at 1 STP, pressure is 1 atm and 273 K. And, at STP, 1 mol of any gas will have the volume of 22.41 liters.

First, find the number of moles.
Use of PV=nRT and solve for n.

PV/RT=n
[(790 mm Hg x 1 atm/760 mm Hg)(0.550 L)] / [ (0.0821 L-atm/mol-K)(27C +273)] = n
0.0232 mol = n

So, you can use PV=nRT now.

V= nRT/P
= [(0.0232 mol)(0.0821 L-atm/mol-K)(273 K)] / [( 1 atm)]
= 0.520 L

Or, you can use the fact that 1 mol at STP is 22.4 L.

1 mol/ 22.4 L = 0.0232 mol/ V
and then solve for V

V= 0.520 L

Or, if you dont want to solve for moles, you can use P1V1/T1 = P2V2/T2.

V2= T2(P1V1) / (T1P2)
=[(273 K)(790 mm Hg x 1 atm/760 mm Hg)(0.550 L)] / [(27C +273)(1 atm)
= 0.520 L

Hope this helps!!

The gas law is PV = nRT. Memorize that. Since N does not change, and R does Not change, you can call them both a constant. That gives you PV = KT which you rewrite as PV/T = K.

Now you introduce your sub1 and sub 2: P1V1/T1 = P2V2/T2 (both equal K so they are equal to each other)

Next you change Centigrade to Absolute and solve the arithmetic.

calculate the number of moles of HCl of STP..

so you know that there are 22.4 liters of one mole of any gas at stp... use it as a conversion factor to get moles.

so, convert 550 ml to L.. then use 550 ml time 1 mole / 22.4 L

then you have moles for n in Pv=nrt, now solve for V!