Do it that way. Use your gas laws.
OK, so V can always be defined as the number of moles of each species, multiplied by Vm
, summed. So we can write it as such, assuming the change in volume is referring to the effects of the reaction itself (no. of moles changing) rather than, say, the container volume being externally changed.
Then the question is what is Vm
: if it's constant, then I just write it in as such; otherwise, using the gas laws, it will be a function of pressure, temperature and nothing else (and then gas constants, depending on which gas law is used). If pressure is non-constant (as a result of changing number of moles of gas), anything I can do to model it?