Does mass affect pressure? I understand volume, and temperature does but not sure about mass. If I have a gas with mass 15 g, wont this exert less pressure than a gas have a mass of 30 g?

Yes, mass does indeed affect pressure. In a closed system, pressure is directly proportional to the amount of force exerted by gas molecules on the walls of the container. The more mass there is in a given volume, the more gas molecules there are, and thus, the more force they exert collectively.

To understand this concept more deeply, we can use the ideal gas law equation, which is expressed as follows:

PV = nRT

Where:
P = Pressure
V = Volume
n = Number of moles
R = Ideal Gas Constant
T = Temperature

According to the ideal gas law, pressure (P) is directly proportional to the number of moles (n) of gas present. The number of moles, in turn, is directly proportional to the mass of the gas.

Since mass affects the number of moles (n) and the number of moles affects pressure (P), it follows that mass also has an impact on pressure.

Using this information, if you have two gases with different masses, the gas with a higher mass will exert more pressure compared to the gas with a lower mass, all other factors being equal.

In your specific example, if you have a gas with a mass of 15 g and another gas with a mass of 30 g, the gas with a mass of 30 g will exert more pressure than the gas with a mass of 15 g, assuming they are at the same temperature and in the same volume.