Learning objectives
The magnitude of Kc can be calculated if the initial concentrations are known for all components of the equilibrium AND the equilibrium concentration of one component is known.
This method depends on the fact that the change in the amount in moles of the one component due to the reaction occurring to reach equilibrium is be related to the change in all other components through the stoichiometry of the reaction.
Consider a system where given amounts of NO and O2 react to give NO2 according to the equation shown.
The concentrations of all reactants and products before reaction occurs are known (initial concentrations).
Additionally, the equilibrium concentration of one component (NO2) is given.
Thus the change in concentration due to reaction of one component (NO2) can be calculated.
Changes due to the reaction for other components (NO and O2) can be deduced using the reaction equation.
Therefore all equilibrium concentration of all components can be deduced and used to calculated Kc.
This activity provides guided problems using the procedure above to calculate Kc.
On completion of the activity you should be able to
This method depends on the fact that the change in the amount in moles of the one component due to the reaction occurring to reach equilibrium is be related to the change in all other components through the stoichiometry of the reaction.
Consider a system where given amounts of NO and O2 react to give NO2 according to the equation shown.
2NO(g) + O2(g)  2NO2(g)
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The concentrations of all reactants and products before reaction occurs are known (initial concentrations).
Additionally, the equilibrium concentration of one component (NO2) is given.
Thus the change in concentration due to reaction of one component (NO2) can be calculated.
Changes due to the reaction for other components (NO and O2) can be deduced using the reaction equation.
Therefore all equilibrium concentration of all components can be deduced and used to calculated Kc.
This activity provides guided problems using the procedure above to calculate Kc.
On completion of the activity you should be able to
- use the given initial and equilibrium concentration for one component to calculate the change due to reaction
- use the calculated change in one component to deduce the change in the other components
- calculate the equilibrium concentration of all components from their initial concentration and the change due to the reaction to reach/restore equilibrium
- calculate Kc for the reaction.