Equilibrium Constants
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What do equilibrium constant allow you to do?
Work out the actual concentration values that occur when changes in temperature happen in a closed system under le chateliers principle.
What is Kc?
equilibrium constant in terms of concentration
What is Kp?
equilibrium constant in terms of partial gas pressures
What are partial gas pressures?
The pressure an individual gas would exert in a mixture if it occupied the whole volume at the same temperature.
What is the relationship between partial pressure and concentration?
Partial pressure is proportional to the concentration of the gas
What are the units of Kc?
Mol and dm
What are the units of Kp?
kPa
What does it mean when the value of Kc is 1?
If Kc = 1, then the equilibrium has equal amounts of starting materials and products.
What does it mean when the value of Kc is greater than 1?
If Kc is much greater than 1, then we have an equilibrium favouring the side of the products, with most of the reactants being converted. This reaction is occurring spontaneously, so ΔG will be negative.
What does it mean when the value of Kc is less than 1?
If Kc is much less than 1, then the equilibrium is favouring the side of the reactants, with very few products being formed. We can relate this to ΔG. As this reaction is not spontaneous, ΔG is positive.
If the forward reaction is exothermic, how does changing the temperature affect the rate constant (Kc)?
Increasing temperature favours the endothermic reaction causing equilibrium to shift left towards the reactants. This means the concentration of products decrease so that the concentration of reactants can increase. This means Kc decreases as the value at the bottom of the equation is larger than the top.
If the forward reaction is endothermic, how does changing the temperature affect the rate constant (Kc)?
Increasing the temperature favours the endothermic direction so equilibrium shifts right towards the products. This means the concentration os reactants decreases so that the concentration of the products can increase. Thus the value of Kc increases.
What is the equation to calculate mole fraction?
Mole fraction of gas X= No of moles of gas X / total no. of moles of gas in mixture
What is the equation to calculate the partial pressure of a gas?
Partial pressure of gas X= (mole fraction of gas X) x (total pressure of the mixture)