Does pressure and volume affect equilibrium?
Pressure change will not affect the equilibrium concentration of solids and liquids. It will only affect the gaseous reactions. For example - There are four moles of reactants that react to form two moles of product.
When there is an increase in pressure, the equilibrium will shift towards the side of the reaction with fewer moles of gas. When there is a decrease in pressure, the equilibrium will shift towards the side of the reaction with more moles of gas.
Because there are more moles of reactants, an increase in volume will shift the equilibrium to the left in order to favor the reactants. When there is a decrease in volume, the equilibrium will shift towards the side of the reaction with fewer moles.
Only three types of stresses can change the composition of an equilibrium mixture: (1) a change in the concentrations (or partial pressures) of the components by adding or removing reactants or products, (2) a change in the total pressure or volume, and (3) a change in the temperature of the system.
Decreasing the pressure
The equilibrium will move in such a way that the pressure increases again. It can do that by producing more gaseous molecules. In this case, the position of equilibrium will move towards the left-hand side of the reaction.
The Relationship between Pressure and Volume: Boyle's Law. As the pressure on a gas increases, the volume of the gas decreases because the gas particles are forced closer together. Conversely, as the pressure on a gas decreases, the gas volume increases because the gas particles can now move farther apart.
Pressure does not affect the value of Kp, just as concentration does not affect the value of Kc. An increase in pressure causes equilibrium to shift in favor of the direction with the fewer moles so that the pressure decreases. The partial pressure ratio of reactant to products stays the same so Kp does not change.
Le Chatelier's principle implies that a pressure increase shifts an equilibrium to the side of the reaction with the fewer number of moles of gas, while a pressure decrease shifts an equilibrium to the side of the reaction with the greater number of moles of gas.
First, let's look at Le Chatelier's principle. If we mechanically decrease the volume of a container of gases the pressure inside the container will increase. Le Chatelier's principle tells us the reaction will re-achieve equilibrium by shifting to counteract this change.
Decreasing the volume of a contained gas will increase its pressure, and increasing its volume will decrease its pressure. In fact, if the volume increases by a certain factor, the pressure decreases by the same factor, and vice versa. Volume-pressure data for an air sample at room temperature are graphed in Figure 5.
What factors affect the equilibrium position and how they effect it?
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The equilibrium position can be changed by adjusting:
- the concentrations of reactants.
- the pressure of reacting gases.
- the temperature at which the process takes place.
A catalyst does not affect the chemical equilibrium. It only speeds up a reaction. In fact, catalyst equally speeds up the forward as well as the reverse reaction.
Two conditions of equilibrium must be satisfied to ensure that an object remains in static equilibrium. Firstly, the net force acting upon the object must be zero. Secondly, the net torque acting upon the object must also be zero.
Catalysts do not affect the equilibrium because they are not involved in the chemical reaction.
How does changing pressure and volume affect equilibrium systems? If you increase the pressure of a system at equilibrium (typically by reducing the volume of the container), the stress will best be reduced by reaction that favors the side with the fewest moles of gas, since fewer moles will occupy the smallest volume.
The amount of substance increases due to the forward reaction. Therefore, an increase in pressure will lower the equilibrium yield.
According to Le Chatelier's principle, if pressure is increased, then the equilibrium shifts to the side with the fewer number of moles of gas. This particular reaction shows a total of 4 mol of gas as reactants and 2 mol of gas as products, so the reaction shifts toward the products side.
Decreasing the concentration of a reactant causes the equilibrium to shift to the left, producing less products. Decreasing the concentration of a product causes the equilibrium to shift to the right, producing more products.
Figure 9.14 The relationship between pressure and volume is inversely proportional.