Topic 7: Equilibrium Flashcards
Chemical Equilibrium
- forward and backward reaction occur at the same rate
- concentration of reactants and products remain constant
- can only occur in a closed system
- equilibrium is dynamic, meaning at a microscopic level the reaction does not stop and the reactants are continuously changing to products and the products are continuously changing into reactants
- there is no change in the any physical properties
Physical Equilibrium
- does not involve a chemical reaction, rather a change in state
- the rate of the foward reaction = the rate of the backward reaction
- the volume of liquid remains constant
- can only occur in a closed system
- equilibrium is dynamic, meaning at a microscopic level, the liquid is continuously getting evaportated and the gas is continuously getting condensed
- physical preoperties remain the same
Equilibrium Constant
- is the ratio between the concentration of products and the concentration of reactants
- can only be changed by temperature
Equilibrium Constant Formula
aA + bB ⇄ cC + dD
Kc = ([C]^c [D]^d)/([A]^a [B]^b)
Kc = products ÷ reactants
What does a large Kc value show?
- concentartion of products is greater than concentration of reactants at equilibrium
- foward reaction is favoured
- mixture mostly contains products
What does a small Kc value show?
- concnetration of reactants is gretaer than concentration of products at equilibrium
- backward reaction is favoured
- mixture mostly contains reactants
What does Kc = 1 show?
- there are equal amounts of reactants and products
Reaction Quotient
- a measure of the relative amounts of products and reactants, when reaction is not at equilibrium
- unlike the equilibrium constant, reaction quotient takes into consieration the concentration of reactants and products even when the reaction is not at equilibrium
- gives an idea of what needs to occur to bring the reaction to equilibrium
If Q < Kc
State what happens for the following scenerio.
- concentration of reactants is greater than the concentration of products
- to bring the reaction to equilibrium, the reactants needs to be decreased
- the foward reaction is favoured to bring reactionn to equilibrium
If Q > Kc
State what happens for the following scenerio.
- concentration of products is greater than the concentration of reactants
- concentration of products needs to be decreaesed to bring the reaction to equilibrium
- the backward reaction is favoured to bring the reaction to equilibrium
If Q = Kc
State what happens for the following scenerio.
- the reaction is at equilibrium
Le Chatelier’s Principle
- the principal predicts how a reaction will respond to one or more changes and what direction the equilibrium will shift
According to Le Chatelier’s principle, what are the parameters that can influence the equilibrium of a reaction
- temperature
- catalyst
- pressure
- concentration
Le Chatelier’s principle
Temperature
Conditions if the enthalpy change (△H) of a system was positive.
- positive enthalpy change means endothermic reaction
- increase in temperature will result in the equilibrium shifting to the product side (or to the right) and the foward reaction will be favoured
- decrease in temperature will result in the equilibrium shifting to the reactant side (or to the left) and the backward reaction will be favoured
Le Chatelier’s principle
Temperature
Conditions if the enthalpy change (△H) of a system was negative.
- negative enthalpy change means exothermic reaction
- increase in temperature will result in the equilibrium shifting to the reactant side and the backward reaction will be favoured
- decrese in temperature will result in the equilibrium shifting to the product side (or to the right) and the foward reaction will be favoured
Le Chatelier’s principle
Catalyst
- addition of catalyst increases the rate of the foward and backward reaction
- position of equilibrium does not change
- the equilibrium is attained faster
Le Chatelier’s principle
Pressure
Number of gas molecules on the product side exceeds the reactant side.
- increase in pressure leads to the equilibrium shifting to the reactant side (or to the left) and the backward reaction is favoured
- decrease in pressure leads to the equilibrium shifting to the product side (or to the rigth) and the foward reaction is favoured
Le Chatelier’s principle
Pressure
Number of gas molecules on the reactant side exceeds the product side.
- Increase in pressure leads to the equilibrium shifting to the product side (or to the right) and the foward reaction is favoured
- Decrease in pressure leads to the equilibrium shifting to the reactant side (or to the left) and the backward reaction is favoured
Le Chatelier’s principle
Concentration
Concentration of reactants increase/concentration of products decrease.
- Q < Kc
- concentration of reactants needs to decrease
- foward reaction is favoured
- equilibrium shifts to the product side (or to the right)
Le Chatelier’s principle
Concentration
Concentration of products increase/concentration of reactants decrease.
- Q > Kc
- concentration of products needs to decrease
- backward reaction is favoured
- equilibrium shifts to the reactant side (or to the left)
Harber Process
- N2(g)+3H2(g) ⇌ 2NH3(g)
- enthalpy change is - 92 kJ/mol, therefore it is a exothermic reaction
- the ammonia produced is used to make synthetic fertilizers, and in the synthesis of nitric acid , polymers and explosives
Harber Process
To maximize the yeild of ammonia from this procees, what several condition need to be met?
- low temperature
- high pressure
- concnetration of product
- catalyst
Harber Process
Low Temperature
- exothermic reaction
- product side will be favoured
- optimum temperature of 450C is used because a lower temperature would slow down the rate of reaction
Harber Process
High Pressure
- the number of gas molecules on the product side is lesser than the number of gas molecules on the reactant side
- foward reaction will be favoured
- optimum pressure of **200 -250 ATM **is used as a high pressure would not be economically feasible
Harber Process
Catalyst
- solid iron (Fe) is used as the catalyst to speed up the rate of reaction and reach equilibrium faster
Contact Process
- 2SO2(g)+O2(g) ⇌ 2SO3(g)
- enthalpy change of - 197 kJ/mol, therefore it is a exothermic reaction
- the sulphuric acid (H2SO4), has many uses which include: fertilizers, dyes, soaps and detergents and paints and pigments.
Contact Process
To maximize the yeild of sulfur trioxide from this procees, what several condition need to be met?
- low temperature
- high pressure
- concentration of product
- catalyst
Contact Process
Low Temperature
- exothermic reaction
- product side is favoured
- optimum temperature of 450C as a lower temperature would slow down the rate of reaction
Conatct Process
High Pressure
- the** # of gas molecules on the product side is lesser** than the # of gas molecules on the reactant side
- foward reaction will be favoured
- optimum pressure of 1 -2 ATM, this pressure is required in order to convert the reactants to products, the reaction is about 97% efficent at this pressure
Contact Process
Concentration of Product
- the sulfur trioxide that is produced is continuously being removed in order to shift the equilibroim to the right and favour the product side
Contact Process
Catalyst
- vanadium pentoxide (Va2O5) is used as a catalyst to speed up the rate of reaction and reach equilibrium faster
