Chemistry question about Boyle's law

Question

To apply Boyle's law to a gas, what properties of the gas must remain constant? Select all that apply.

1. amount in moles
2. volume
3. pressure
4. temperature

I know the temperature should remain constant but the amount in moles should remain too?

Answer 1

The ideal gas law says PV=nRT. If we assume that a gas is in a closed container where no gas is let in and none escapes, then we can calculate how pressure, temperature, and volume change over time.

If PV = nRT, then using algebra, we can solve for nR to get nR = PV/T.

In a closed container, the number of moles of the gas will not change. And R is a constant as well. So if P₁, V₁, T₁, are the pressure, volume, and temperature at time 1, and P₂, V₂, and T₂ are the pressure, volume, and temperature at time 2, then (since nR don't change P₁V₁/T₁ = nR = P₂V₂/T₂ or:

P₁V₁/T₁ = P₂V₂/T₂

Boyle's Law says P₁V₁ = P₂V₂ so, iyou can see that temperature has been removed from the equation. That's because they assume that temperature is held constant so does not play a part in this particular situation.

So, the amount of moles must be constant (the gas must be in a sealed container where nothing escapes and nothing comes in) and temperature must be constant.