Topic 11.1 Further Equilibrium Flashcards
Homogenous
A homogenous is where all the reactants are in the same phase (state)
Heterogenous
A heterogeneous is where all reactants and products are in different phases (states)
Equilibrium constant: Kc
Equilibrium constant using concentration
—> only affected by temperature
(can be obtained experimentally or by using thermodynamic data)
Equilibrium constant: Kp
Equilibrium constant using partial pressures
(Temperature is the only factor that will affect Kp)
Partial pressures
-Used to express the concentration of gases in reactions
-Partial pressure of an individual gas is the pressure that the gas would exert alone if it occupied the volume of the mixture
Calculating partial pressure
Calculating individual partial pressures using the mole fraction and the total pressure:
P= toatal pressure of the system
PA= partial pressure
Qc reaction quotient
-Mathematical relationship between the concentrations of the components of an equilibrium mixture
-When concentration of one of the compounds is changed then the value of Qc changes and is no longer equal to Kc
-The equilibrium composition changes until Qc = Kc
Effect of pressure on Qc
If the partial pressure of one component gases is changed we predict the overall effect in the same way as we did with Kc
(At a constant temperature, a change in pressure has no effect on Kc and Kp)
Writing equilibrium constants for heterogenous
Eg: CaCO3(s) ⇌ CaO(s) + CO2
we obtain:
[CaO(s)][CO2(g)]
———————— = a constant
[CaCO3(s)]
The effect of temperature on Kc and Kp
-Exothermic reaction: the value of Kp decreases with increasing temperature
(Increase in temp. decreases forward reaction; equilibrium favours left; increases the conc. of reactant; decreases conc. of products)
-Endothermic reaction: the opposite occurs
(the same trend with Kc)
The effect of temperature on equilibrium position
If a equilibrium constant for a reaction changes with a change in temperature, then it follows that the equilibrium position also changes.
—> Increasing temp. equilibrium shifts to endothermic reaction.
—> Decreasing temp. quilibrium shifts to exothermic reaction.
The effect of concentration on Kc and Kp
When the concentration of one of the components is altered, there is an immediate change of Qc.
At this point Qc ≠ Kc.
Therefore equilibrium composition changes until Qc = Kc.
The effect of pressure on Kc and Kp
At a constant temperature, a change in pressure has no effect on Kc and Kp.
The effect of adding a catalyst on Kc and Kp
The catalyst does not affect the value of the equilibrium constant so the equilibrium position does not change.
(The catalyst does not appear in the overall equation so cannot influence the value of the equilibrium constant).
