Moles and PTVN problems

Question

I am confused....

If I have 500mL for my initial volume and 350mL for my final volume, this means that the effect is decreasing, I also have 0.0166 moles for my initial number of molecules. It is asking what my final number of moles is, but in order to solve that, I have to figure out whether the effect on the moles is increasing or decreasing. Doesn't it stay the same? If so how do I solve the problem then?

Answer 1

The number of moles WILL stay the same unless you add or remove some of the gas. Changing the volume by changing the pressure (without adding or removing gas) will not affect the number of moles. Now, the way you write the question, it appears that some gas has leaked out and the volume has gone from 500 ml to 350 ml. You say "the effect is decreasing", but what is "the effect"? If gas has leaked out, the number of moles will decrease by the same fraction, i.e. 0.7 or 70% and the moles remaining will be 0.0116 moles.