Edexcel IGCSE Chemistry - Reversible Reactions

what is a reversible reaction?

a reaction which can go both ways - the products of a reaction can react with each other and convert back to the original reactants

what is the symbol for a reversible reaction?

which examples of reversible reactions are there?

• thermal decomposition of ammonium chloride

• dehydration of copper (II) sulfate

describe the thermal decomposition of ammonium chloride

• ammonium chloride is a white solid

• when it is heated it breaks down into ammonia and hydrogen chloride (colourless gases)

• if you let it cool the products react together to form ammonium chloride

describe the dehydration of copper (II) sulphate

• wet copper (II) sulfate is blue

• when it is heated the water evaporates off it

• dry copper (II) sulfate is white

• if you add water it becomes blue again

what happens if a reversible reaction takes place in a closed system?

equilibrium will be reached

what type of equilibrium do reversible reactions reach?

dynamic equilibrium

what condition is required for dynamic equilibrium?

a closed system

what are the 2 characteristics of dynamic equilibrium?

• the concentrations of reactants and products remain constant

• the forwards and reverse reactions are happening at the same rate

what can shift in a reversible reaction?

position of equilibrium

what do all reversible reactions have?

• one reaction as exothermic

• one reaction as endothermic

which two conditions can you change to alter the position of equilibrium?

• temperature

• pressure

what does altering the position of equilibrium change?

the amount of products and reactants formed

what happens if you increase the temperature of a reversible reaction?

• equilibrium shifts in the endothermic direction (left/right) (positive enthalpy change)

• to oppose the change

• making (less/more products) and yield of x (increases/decreases)

what happens if you decrease the temperature of a reversible reaction?

• equilibrium shifts in the exothermic direction (left/right) (negative enthalpy change)

• to oppose the change

• making (less/more products) and yield of x (increases/decreases)

what happens if you increase the pressure of a reversible reaction?

• equilibrium will shift to the side/in the direction that produces fewer gas moles (left/right)

• to oppose the change

• this makes (less/more products) and the yield of x (decreases/increases)

what happens if you decrease the pressure of a reversible reaction?

• equilibrium will shift to the side/in the direction that produces more gas moles (left/right)

• to oppose the change

• this makes (less/more products) and the yield of x (decreases/increases)

what effect does a catalyst have on the position of equilibrium?

no effect

why does a catalyst not change the position of equilibrium?

it increases the rates of the forwards and backwards reactions equally