# Thread: In which of the following will the gas exert the most pressure?

1. ## In which of the following will the gas exert the most pressure?

Four cylinders filled with gas are at the same temperature. In which of the following will the gas exert the most pressure?
A) A 2.0 L cylinder containing 4.0 g of H2.
B) A 2.0 L cylinder containing 4.0 g of He.
C) A 1.0 L cylinder containing 16.0 g of O2
D) None. At constant temperature, pressure is constant.

*I understand that when volume decreases, pressure increases but that is about all I know. Here it involves mass, molar mass and volumes and I don't know how to relate that to the basic knowledge I have that I just mentioned (volume decreases when pressure increases).

2. Originally Posted by s3a
Four cylinders filled with gas are at the same temperature. In which of the following will the gas exert the most pressure?
A) A 2.0 L cylinder containing 4.0 g of H2.
B) A 2.0 L cylinder containing 4.0 g of He.
C) A 1.0 L cylinder containing 16.0 g of O2
D) None. At constant temperature, pressure is constant.

*I understand that when volume decreases, pressure increases but that is about all I know. Here it involves mass, molar mass and volumes and I don't know how to relate that to the basic knowledge I have that I just mentioned (volume decreases when pressure increases).
are you familiar with the ideal gas law PV = nRT?

we have

P = nRT/V

calculate this for each of the gases and see which has the largest value

3. Temperature is constant so I can choose ANY TEMPERATURE I WANT AND APPLY IT TO THE FORMULA FOR EACH 4 CASES?

4. Originally Posted by s3a
Temperature is constant so I can choose ANY TEMPERATURE I WANT AND APPLY IT TO THE FORMULA FOR EACH 4 CASES?
no, just leave it as T and find an expression for each formula in terms of T

for instance, say for gas 1: P = 2T

and for gas 2: P = 3T

then clearly, whatever T is (as long as it is positive) 3T is bigger than 2T and so we would say gas 1 has more pressure. and so on, so you will be able to figure it out even if T is unknown