OCR A-Level Chemistry: Chapter 19 - Equilibrium
This flashcard set explains how to determine units for the equilibrium constant Kc, distinguishes between homogeneous and heterogeneous equilibria, and outlines key gas-phase concepts like mole fraction and partial pressure used in equilibrium calculations.
How are the units of Kc worked out?
Substitute units into the expression
Cancel common units
Key Terms
How are the units of Kc worked out?
Substitute units into the expression
Cancel common units
What is a homogeneous equilibrium?
Equilibrium species all have the same state.
What is a heterogeneous equilibrium?
Equilibrium species that have different states.
In a heterogeneous equilibrium, what is discounted in the expression for Kc?
Any species that are not as a gas or in solution.
What is a mole fraction?
The proportion of the volume of a gas to the total volume of gases in the mixture.
What is the partial pressure?
The contribution that the gas makes towards the total pressure P.
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| Term | Definition |
|---|---|
How are the units of Kc worked out? | Substitute units into the expression Cancel common units |
What is a homogeneous equilibrium? | Equilibrium species all have the same state. |
| Equilibrium species that have different states. |
In a heterogeneous equilibrium, what is discounted in the expression for Kc? | Any species that are not as a gas or in solution. |
What is a mole fraction? | The proportion of the volume of a gas to the total volume of gases in the mixture. |
What is the partial pressure? | The contribution that the gas makes towards the total pressure P. |
How is a mole fraction calculated? | Mole fraction χ(A) = n(A)/n(total) |
How is partial pressure calculated? | p(A) = mole fraction x total pressure P p(A) = χ(A) x P |
What is the way to check the partial pressures are correct? | Sum of the partial pressures equals the total pressure. |
With the equilibrium H(2) + I(2) 2HI, what is the expression for Kp? | Kp = p(HI)^2 / p(H(2)) x p(I(2)) |
What does the magnitude of an equilibrium constant represent? | The extent of an equilibrium |
What would K=1, K=100 and K=0.01 represent? | K=1: equilibrium halfway between reactants and products |
What is the effect on K when the temperature is increased and the forward reaction is exothermic? | Equilibrium constant decreases Equilibrium shifts to reactant side |
What is the effect on K when the temperature is increased and the forward reaction is endothermic? | Equilibrium constant increases Equilibrium shifts to product side |
What effect does increasing pressure have on a reaction with fewer moles of gaseous products than reactants? | Products increase |
What effect does increasing pressure have on a reaction with the same number of moles of gaseous products and reactants? | No change Equilibrium stays the same |
What is the effect of a catalyst on the equilibrium constant? | Catalysts affect the rate but not the equilibrium position. Equilibrium is reached faster but position does not change. |