Unit 8 Flashcards
Dynamic equilbrium
The rate of the forward reaction is the same as the rate of the backward reaction in a closed system
The concentrations of the reactants and products are constant
Closed system
none of the reactants or products escape from the reaction mixture
Open system
some matter is lost to the surroundings
Equilibrium law
explains how the equilibrium constant, K, can be found from the stoichiometry of the reaction
Equilibrium constant expression
expression that links the equilibrium constant, K, to the concentrations of reactants and products at equilibrium taking the stoichiometry of the equation into account
Equilibrium constant formula
aA + bB ⇌ cC + dD
K = (C)^C * (D)^D / (A)^A * (B)^B
- [A] and [B] = equilibrium reactant concentrations (mol dm-3)
- [C] and [D] = equilibrium product concentrations (mol dm-3)
- a, b, c and d = number of moles of corresponding reactants and products
- Solids are ignored in equilibrium constant expressions
Size of equilibrium constnat
tells us how the equilibrium mixture is made up with respect to reactants and products
What happens if equilibrium constant K > 1
The concentration of products is greater than the concentration of reactants and we say that the equilibrium lies to the right hand side. When K»1, reaction almost goes to completion
What happens if equilibrium constant K=1
there are significant amounts of both reactants and products and equilibrium does not lie in favour of either the reactants or products
What happens if equilibrium constant K<1
then the concentration of reactants is greater than the concentration of products and we say that the equilibrium lies to the left hand side. When K«1, reaction hardly proceeds.
Relationship between K values that are reverse of each other
K(reverse) = 1 / K(forward)
Position of equilibrium
relative amounts of products and reactants in an equilibrium mixture.
- When the position of equilibrium shifts to the left, it means the concentration of reactants increases
- When the position of equilibrium shifts to the right, it means the concentration of products increases
Le chatelier’s principle
if a change is made to a system at dynamic equilibrium, the position of the equilibrium moves to minimize this change, used to predict changes to the position of equilibrium when there are changes in temperature, pressure or concentration
Effect of concentration on position of equilibrium
- The value of Kc does not change.
- When a concentration of a substance increases: To re-decrease the substance’s concentration, it favors the opposite side
When a concentration of a substance decreases : To re-increase the substance’s concentration, it favors that side
Effect of pressure on position of equilibrium
- The value of Kc does not change.
- When pressure increases, favors the side with less moles of gas. Less gas means less collision of gas particles with the container’s wall, so the pressure decreases.
- When pressure decreases, Favors the side with more moles of gas. More gas means more collision of gas particles with the container’s wall, so the pressure increases.
Effect of temperature on position of equilibrium
- When temperature increases, favors endothermic reaction to absorb energy and re-decrease the temperature.
- When temperature decreases, favors exothermic reaction to release energy and re-increase the temperature.
Effect of temperature on equilibrium constant K value
- When temperature changes and forward reaction favored, Kc Increases
- When temperature changes and reverse reaction favored, Kc decreases
Effect of catalysts on position of equilibrium
Catalysts only cause a reaction to reach its equilibrium faster and therefore have no effect on the position of the equilibrium or on the value of K
Heterogenous equilibria example
- in a fizzy drink bottle, an equilibrium exists between the dissolved CO2 and gaseous
- When the bottle is opened, some CO2 (g) escapes, the equilibrium shifts to the left to reduce the effect of this change and bubbles of CO2 (g) are observed
