The first case: the volume can be changed: if the pressure increases, the piston can be squeezed inward. At this time, if the pressure increases, it should move in the direction of decreasing pressure. If the pressure decreases, the total number of molecules in the gas after the reaction will also decrease, such as the balance of 2SO2+O2==2SO3. If the piston pushes inward, the pressure increases and the balance moves to the right, if there are 5mol of sulfur dioxide, 5mol of oxygen and 5mol of tri in the original volume. Then, after the reaction, it is assumed that there are 3mol of sulfur dioxide, 4mol of oxygen and 7mol of sulfur trioxide, the total amount of raw gas is 15mol, and the total volume of gas after the reaction is 14mol. Moreover, after reaching equilibrium, the pressure in the container is the same as atmospheric pressure, and the pressure before the reaction is the same, that is, the pressure before and after the reaction is the same. According to clabolone equation pv=nrt,
In the second case, the volume of the container cannot be changed. There are two situations. One is to charge a gas unrelated to the reaction, such as helium, and the mass fraction of each substance in the container remains unchanged, and the balance will not move at this time; There is also a charged reaction gas, so it is good to do it according to the general equilibrium motion at this time.
I don't know if you are aware of this.