CHEMISTRY COMMUNITY

Does the equilibrium shift if pressure is changed? If so, why?

The equilibrium does change when pressure changes due to the fact that when you change pressure you can change the volume in which the reactants/products are kept in which subsequently changes the concentrations of the products/reactants which can then change the Q value and indicate which way the reaction will proceed. The short cut in which Dr. Lavelle addressed in class is to look at the number of mols indicated by the balanced equation of the reactants. When the pressure is increased then the reaction will favor the side with the least number of total mols.

The equilibrium only changes if the change in pressure is due to a changing volume. If the volume decreases, the pressure will increase and the reaction will try to stabilize by decreasing pressure and the system will shift to the side with less moles of gas. However, if pressure changes due to an inert gas, there is no change in equilibrium and the new inert gas has no effect on the reaction or concentrations of reactants or products.

reaction response to minimize the effect of an increasing pressure by decreasing volume. When volume decreases and there are more moles of gas on the left then the reaction --> and favors products. When volume decreases and there are more moles of gas on the right then the reaction <---- favors reactants.

The K value is same though.

Look at how many mols are on both sides of the equation. If the pressure increases, the equilibrium shifts towards the side with less mols.

Can the Q value change if the pressure is changed?

The equilibrium will shift to the side of the equation where there are less moles of gas if the pressure is increased by decreasing volume. If an inert gas is pumped in, the reaction will neither favor forward nor backward. The reason the pressure change moves the equation to one side is because Concentration= moles divided by Volume, if volume is cut in half, concentration doubles. depending on if Q is greater or less than Kp, the equilibrium will shift reverse or forwards respectively.

Why does a change in pressure due to an inert gas not affect the equilibrium?