Equilibrium Key Terms and Processes Flashcards
Year 1 and Year 2
Dynamic Equilibrium
the rate of the forwards reaction is equal to the rate of the backwards reaction, and the concentrations of the reactants and products do not change
Le Chatelier’s Principle
When a system in equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of that change
Effect of temperature when the forwards reaction is exothermic (-ve ΔH)
Increased temperature;
Position of equilibrium moves to the LHS; more reactants are made
Decreased temperature;
Position of the equilibrium shifts to the RHS, more products are made
Effect of temperature when the forwards reaction is endothermic (+ve ΔH)
Increased temperature;
Position of the equilibrium moves to the RHS, more products are made
Decreased temperature;
Position of the equilibrium moves to the LHS, more reactants are made
Effect of pressure on a system
Increasing the pressure of the system will shift the position of the equilibrium to the side where the lowest volume of moles are created.
Decreasing the pressure of the system will shift the position of the equilibrium to the side where the most volume of moles are created
The effect of a catalyst on equilibrium
A catalyst has no effect on the the position of the equilibrium, it simply speeds up the rates of the forwards and backwards reaction. It increases the rate at which equilibrium is reached.
In Kc calculations , square brackets are representative of…?
Concentration
The Equilibrium law/Kc equation
[reactants]
Kc = 1 ?
position of equilibrium between
Kc > 1 ?
Position of equilibrium is towards the products
Kc < 1 ?
Position of equilibrium is towards the reactants
Homogeneous Equilibria
Contains equilibrium species that all have the same state or phase.
Heterogeneous Equilibria
Contains equilibrium species that have different states or phases.
Mole Fraction
The mole fraction of a gas is the same as its proportion by volume to the total volume of gases in a gas mixture
Partial Pressure
partial pressure =
mole fraction x total pressure
K = 100
indicates an equilibrium well in favour of the products
K = 1 x 10^-2
indictates an equilibrium well in favour of the reactants
At a set temperature Kc is..?
..constant and does not change despite any modifications to concentration, pressure or the presence of a catalyst.
When temperature is changed, Kc..?
Kc also changes, it is the only variable that will change the value of Kc
If the forwards reaction is exothermic and the temperature is raised, the equilibrium constant …
… decreases with increasing temperature, raising the temperature decreases the equilibrium yield of products, which means in the Kc equation the numerator will get smaller, while the denominator will get larger, which makes Kc smaller
If the forwards reaction is endothermic and the temperature is raised, the equilibrium constant…
…increases with increasing temperature, raising the temperature increases the equilibrium yield of products, which means that in the Kc equation the numerator will get larger, while the denominator will get smaller, which makes Kc larger
How do temperature and pressure affect equilibrium constants?
The value of an equilibrium constant Kc is seemingly unaffected by by changes in concentration and pressure
