Hello, Emma,
Ishwar has the correct answer, and a nice explanation. I only want to suggest an equation that I find to be very useful. In applies to all the gas laws when there are no changes in the moles of gas, n, in the PV=nRT ideal gas law.
When comparing two states of the same gas, I always count on the following:
P1V1/T1 = P2V2/T2
This covers all possible combinations of temperature, pressure, and volume between states 1 and 2 for problems in which there is no removal or addition of any gases. As an example, if a problem asks for the inital pressure, and values for the other variables are provided, we can rearrange the equation for the unknown, in this case P1:
P1 = P2(V2/V1)(T1/T2)
We can easily see that the initial pressure can be predicted from adjustments to the final pressure, P2, which are simply the ratios (V2/V1) and (T1/T2). This simplified expression is derived from the ideal gas law. Since no moles of gas are altered, the n in both equations cancel, as does R, the gas constant. If another variable is also held constant (e.g., the volume) then that ratio also cancels to 1. Makes it easier to compare conditions.
I confess I had a hard time remembering which was Boyle's Law and which was Charles Law. It is easier for me to remember p1V1 over T1 equals P2V2 over T2. Maybe you'll remember those better than I can.
Bob
