Equilibria A2 Flashcards
Define Kc.
Kc is the equilibrium constant for concentrations. It measures the ratio of product concentrations to reactant concentrations at equilibrium.
How is Kc calculated?
Molar concentration of the products/reactants, with powers based on the number of moles of each present in the balanced equation
How are expressions for Kc constructed for homogeneous equilibria?
For homogeneous equilibria (same phase), the Kc expression includes concentrations of substances in that phase.
What is omitted in the Kc expression for heterogeneous equilibria?
For heterogeneous equilibria (different phases), solids and liquids are not included in the Kc expression.
What happens to Kc when the temperature increases in an endothermic reaction?
In an endothermic reaction, an increase in temperature shifts the equilibrium position to favor the products, increasing Kc.
What happens to Kc when the temperature increases in an exothermic reaction?
In an exothermic reaction, an increase in temperature shifts the equilibrium position to favor the reactants, decreasing Kc.
How does an increase in reactant concentration affect Kc?
An increase in reactant concentration shifts the equilibrium towards the product side, increasing Kc.
How does an increase in pressure (for gases) affect Kc?
An increase in pressure shifts the equilibrium toward the side with fewer moles of gas, changing Kc accordingly (for gas-phase reactions).
What is reaction rate?
The change in concentration of a reactant or product in a given time.
What makes an effective collision?
Particles must have sufficient energy
Particles must collide in correct orientation
Which factors can change the rate of a chemical reaction?
Concentration
Temperature
Use of a catalyst
Surface area of solid reactants
What effect does increasing temperature have on reaction rate?
Reaction rate increases
Explain why increasing temperature has its effect on reaction rate
Particles have more energy
Higher speed
Collide more frequently
More successful collisions
Rate increases
What is the rule of thumb for reaction rate and temperature?
A 10C increase in temperature doubles the rate.
What effect does increasing concentration/pressure have on reaction rate?
Reaction rate increases
Explain why increasing concentration/pressure has its effect on reaction rate
Concentration increases
More particles per unit volume
More frequent collisions
More successful collisions
Rate increases
How can progress of a chemical reaction be followed?
Monitoring the removal of a reactant.
Following the formation of a product.
What are the two methods of determining reaction rate, when a gas is produced?
Monitoring the volume of gas produced
Monitoring the loss of mass of reactants
What does a catalyst do?
A substance that changes the rate of a chemical reaction without undergoing any permanent change itself.
What are the main properties of a catalyst?
Not used up in the reaction.
May react with a reactant to form an intermediate or provide a surface for the reaction to take place.
The catalyst is regenerated at the end of the reaction.
What is a homogeneous catalyst?
Has the same physical state as the reactants.
How does a homogeneous catalyst interact with the reactants?
Forms an intermediate
This intermediate breaks down to give the product and regenerates the catalyst
Give two examples of homogeneous catalysts
Sulphuric acid in the production of esters
Chlorine radicals in ozone depletion
How are the units of Kc worked out?
Substitute units into the expression
Cancel common units
In a heterogeneous equilibrium, what is discounted in the expression for Kc?
Any species that are not a gas or in solution (aqueous) .
so solids and liquids are ommited
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.
mole fraction equation?
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.
what is Kp?
Kp is the equilibrium constant using gases.
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
K=100: equilibrium in favour of products
K=0.01: equilibrium in favour of reactants
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
so Reactants decrease
so Equilibrium shifts to right
What effect does increasing pressure have on a reaction with more moles of gaseous products than reactants?
Products decrease
Reactants increase
Equilibrium shifts to left
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.
