When reaction systems at equilibrium are subjected to a disturbance, the equilibrium adjusts to minimize the effect of the disturbance.
For equilibria involving gases, a change in the overall pressure results in a change in equlibrium composition for reactions IF the total number of gas particles in the reactants is different to the total number of gas particles in the products.
Examples:
2SO2(g) + O2(g)
2SO3(g) (3 moles of gases in reactants gives 2 moles in products)
If the reaction is carried out at constant volume, the overall pressure decreases as reaction proceeds.
2N2O(g) 2N2(g) + O2(g) (2 moles of gases in reactants gives 3 moles in products)
If the reaction is carried out at constant volume, the overall pressure increases as reaction proceeds.
The nature of the change in equilibrium composition depends on whether pressure increases or decreases.
The change in composition can be predicted from the fact that net reaction occurs to counteract the change in pressure.
This principle is used in reactions that are carried out on a commercial scale in order to obtain the maximum amount of the substance desired.
For equilibria involving gases, a change in the overall pressure results in a change in equlibrium composition for reactions IF the total number of gas particles in the reactants is different to the total number of gas particles in the products.
Examples:
2SO2(g) + O2(g)
2SO3(g) (3 moles of gases in reactants gives 2 moles in products)If the reaction is carried out at constant volume, the overall pressure decreases as reaction proceeds.
2N2O(g)
2N2(g) + O2(g) (2 moles of gases in reactants gives 3 moles in products) If the reaction is carried out at constant volume, the overall pressure increases as reaction proceeds.
The nature of the change in equilibrium composition depends on whether pressure increases or decreases.
The change in composition can be predicted from the fact that net reaction occurs to counteract the change in pressure.
To restore equilibrium after an increase in pressure, net reaction to form fewer gas particles and decrease pressure occurs.
For the SO3, SO2, O2 equilibrium, net reaction would occur to form SO3. When equilibrium is restored, the pressures of all gases are increased but the increase in pressure of SO3 is greater than for SO2 or O2 because SO3 is formed in the reaction to reaction equlibrium.
For the N2O, N2, O2 equilibrium net reaction would occur to form N2O. When equilibrium is restored, the pressure increase for this gas would be greater than for N2 and O2.
To restore equilibrum after a decrease in pressure (or an increase in volume) net reaction occrs to form more gas particles and increase the pressure.
For the SO3, SO2, O2 equlibrium, net reaction would form SO2 and O2 to increase the pressure. When equilibrium is restored, the pressure of all gases would be decreased, but the pressure of SO3 would decrease to the greatest extent since it is consumed in the reaction to restore equilibrium.
For the N2O, N2, O2 equilibrium will result in net reaction to form N2 and O2 and increase the pressure. When equilibrium is restored, the pressures of all gases will be decreased, but the decrease in the pressure of N2O will be greater than for N2 and O2 due to N2O having been consumed in the reaction to restore equilibrium.
For the SO3, SO2, O2 equilibrium, net reaction would occur to form SO3. When equilibrium is restored, the pressures of all gases are increased but the increase in pressure of SO3 is greater than for SO2 or O2 because SO3 is formed in the reaction to reaction equlibrium.
For the N2O, N2, O2 equilibrium net reaction would occur to form N2O. When equilibrium is restored, the pressure increase for this gas would be greater than for N2 and O2.
To restore equilibrum after a decrease in pressure (or an increase in volume) net reaction occrs to form more gas particles and increase the pressure.
For the SO3, SO2, O2 equlibrium, net reaction would form SO2 and O2 to increase the pressure. When equilibrium is restored, the pressure of all gases would be decreased, but the pressure of SO3 would decrease to the greatest extent since it is consumed in the reaction to restore equilibrium.
For the N2O, N2, O2 equilibrium will result in net reaction to form N2 and O2 and increase the pressure. When equilibrium is restored, the pressures of all gases will be decreased, but the decrease in the pressure of N2O will be greater than for N2 and O2 due to N2O having been consumed in the reaction to restore equilibrium.