## Decrease in volume

$PV=nRT$

904611851
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

### Decrease in volume

For the equation:
2HCl(g) + I(s) --> 2HI(g) + Cl2(g)

why does the number of moles of HCl increase when the volume in the container decreases?

Ronald Yang 2F
Posts: 86
Joined: Fri Sep 25, 2015 3:00 am

### Re: Decrease in volume

If the volume of the container decreases, essentially pressure in the container increases (pressure and volume have an inverse relationship). This pressure is created by the collisions of gas molecules. Thus, we only look at molecules in the gas phase. For 2HCl(g) + I(s) --> 2HI(g) + Cl2(g), we only look at the HCl, HI, and Cl2, so, to balance out the increase in pressure, the reaction shifts to the side with less moles, which is the left side. Thus, the number of moles of HCl would increase.