A Levels Chemistry

Which equations apply to an ideal gas?
[p = pressure, V = volume, M = molar mass, p = density, c = concentration, R = gas constant,
T= temperature]
PRT
2 pV = MRT
cRT
3 pV =
M
1
p =
M


Choice D is correct for the following reasons:

The equation p = ρRT/M is correct. 

It connects pressure, density, temperature, and molar mass for an ideal gas, and is derived from the Ideal Gas Law:

pV = nRT 

n = m/M, where m = mass of gas 

pV = (m/M)RT 

p = mRT/MV 

p = (m/V) x RT/M 

p = ρ x RT/M

The equation pV = MRT is incorrect. 

The correct equation for an ideal gas is pV = nRT, where n represents the number of moles.

The equation pV = cRT/M is incorrect. 

The correct equation for an ideal gas is pV = nRT, which can be transformed into p = cRT, where c is the concentration (n/V):

pV = nRT 

p = nRT/V 

p = (n/V) x RT 

p = c x RT

Choices A, B, and C are incorrect because they include one or both of the incorrect equations, 2 and/or 3.

States of Matter | 2011 - M/J - 9701/12 | Q33