Define the term reversible reaction.
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Define the term reversible reaction.
A reversible reaction is a reaction that can occur in both directions: the forward reaction (which forms the products) and the reverse direction (which forms the reactants).
How are reversible reactions represented in chemical equations?
Reversible reactions are represented using two opposing arrows, ⇌.
When ammonium chloride is heated, what are the products of the reaction?
When ammonium chloride is heated, ammonia and hydrogen chloride are formed.
Write the balanced symbol equation for the reaction that occurs when ammonium chloride is heated.
The balanced symbol equation for the reaction that occurs when ammonium chloride is heated is:
NH4Cl (s) ⇌ NH3 (g) + HCl (g)
True or False?
The reverse reaction can also be called the backwards reaction.
True.
The reverse reaction can also be called the backwards reaction.
True or False?
If a reaction is exothermic in one direction, it is endothermic in the opposite direction.
True.
If a reaction is exothermic in one direction, it is endothermic in the opposite direction.
State what is observed when hydrated copper sulfate is heated.
When hydrated copper sulfate is heated the colour change is blue to white and colourless liquid (water) collects at the top of the test tube.
What is an anhydrous salt?
Anhydrous salts are those that have lost their water of crystallisation.
State the equation for the reversible reaction when hydrated copper(II) sulfate, CuSO4.5H2O, is heated.
The equation for the reversible reaction when copper(II) sulfate is heated is:
CuSO4.5H2O ⇌ CuSO4 + 5H2O
True or False?
Different amounts of energy are transferred in a forward and reverse reaction.
False.
The same amount of energy is transferred in the forward and reverse reactions.
Is the formation of hydrated copper(II) sulfate, from anhydrous copper(II) sulfate an exothermic or endothermic reaction?
The formation of hydrated copper(II) sulfate, from anhydrous copper(II) sulfate is an exothermic reaction.
Describe two features of a system at equilibrium.
Two features of a system at equilibrium are:
The rate of the forward reaction equals the rate of the reverse reaction
The concentrations of reactants and products remain constant.
Define the term closed system.
A closed system is a system where none of the reactants or products can enter or leave the reaction vessel.
True or False?
Equilibrium can only be reached in a closed system.
True.
Dynamic equilibrium can only occur in a closed system as none of the reactants or products are able to leave the reaction vessel.
What is Le Chatelier's Principle?
(Higher tier only)
Le Chatelier's principle states that if a change is made to the conditions of a system, the system will respond to counteract the change.
Give three conditions that can change and alter the position of equilibrium.
(Higher tier only)
Three conditions that can change and alter the position of equilibrium are:
Concentration
Temperature
Pressure
If there is an increase in the amount of products formed, what has happened to the position of equilibrium? (Higher tier only)
If there is an increase in the amount of products formed, the equilibrium has shifted to the right.
True or False?
The position of equilibrium is said to shift to the right if the forward reaction is favoured.
(Higher tier only)
True.
The position of equilibrium is said to shift to the right if the forward reaction is favoured.
If there is an increase in the amount of reactants formed, what has happened to the position of equilibrium? (Higher tier only)
If there is an increase in the amount of reactants formed, the equilibrium has shifted to the left.
What is the effect of decreasing the concentration of a product? (Higher tier only)
If the concentration of a product is decreased, more reactants will react until equilibrium is reached.
If the concentration of a reactant decreases, how does the equilibrium shift? (Higher tier only)
Equilibrium shifts to the left to reduce the effect of a decrease in reactant (or an increase in the concentration of product).
In a reversible reaction, when is the concentration of the reactants the highest? (Higher tier only)
In a reversible reaction, the concentration of the reactants is highest at the start of the reaction.
Describe what happens if the concentration of Fe3+ ions is decreased.
Fe3+ (aq) + SCN- (aq) ⇌ FeSCN2+ (aq)
(Higher tier only)
If the concentration of Fe3+ ions is decreased the rate of the reverse reaction increases to counteract the change, lowering the yield of FeSCN2+
What is an exothermic reaction?
An exothermic reaction is one in which energy it released to the surroundings resulting in the temperature increasing.
What is an endothermic reaction?
An endothermic reaction is one in which energy is taken in from the surroundings resulting in the temperature decreasing.
True or False?
If the forward reaction is exothermic, the backward reaction is favoured by increasing the temperature. (Higher tier only)
False.
If the forward reaction is exothermic, the backward reaction is favoured by decreasing the temperature.
If the forward reaction is endothermic, would a high or low temperature increase the yield of products? (Higher tier only)
If the forward reaction is endothermic, a high temperature would increase the yield of products.
This is because the forward reaction is endothermic. A high temperature would favour the endothermic pathway to oppose the increase.
True or False?
Cooling an exothermic reaction results in the equilibrium shifting in the exothermic direction.
(Higher tier only)
True.
Cooling an exothermic reaction results in the equilibrium shifting in the exothermic direction to produce more heat and raise the temperature.
The following reaction is exothermic.
ICl (l) + Cl2 (g) ⇌ ICl3 (s)
What happens to the yield of ICl3 if the temperature of the reaction is decreased?
(Higher tier only)
If the temperature of the reaction is decreased the yield of ICl3 will increase because the forward reaction is exothermic and will be favoured to counteract the decrease in temperature.
How many molecules of reactant are there in the following reaction?
C2H4 (g) + H2O (g) ⇌ C2H5OH (g)
(Higher tier only)
There are two molecules of reactant in the reaction, one molecule of C2H4 and one molecule of H2O.
Why will changing pressure not affect the position of equilibrium in the following reaction?
H2 (g) + I2 (g) ⇌ 2HI (g)
(Higher tier only)
Changing pressure will not affect the position of equilibrium because there are the same number of molecules on each side of the equation.
In the following system, would an increase or decrease in pressure favour the forward reaction?
2A + 2B ⇌ C + D
(Higher tier only)
Increasing the pressure would favour the forward reaction.
This is because there are 4 molecules on the left and side and 2 molecules on the right hand side.
An increase in pressure will favour the side with the fewest number of molecules.
If the pressure of a system decreases, how does the equilibrium of a reaction shift?
(Higher tier only)
Equilibrium shifts in the direction that produces the larger number of molecules of gas to increase the pressure again.
True or False?
Increasing pressure shifts the equilibrium to favour the side with more gas molecules.
(Higher tier only)
False.
Increasing pressure shifts the equilibrium to favour the side with fewer gas molecules.
What will happen to the yield of product if pressure is decreased?
CO (g) + 2H2 (g) ⇌ CH3OH (g)
(Higher tier only)
If pressure is decreased, the yield of product will also decrease.
This is because the reverse reaction will be favoured due to having a higher number of molecules.
What sort of pressure is needed to obtain a high yield of product?
CO (g) + 2H2 (g) ⇌ CH3OH (g)
(Higher tier only)
High pressure is needed to obtain a high yield of product.
This is because to counteract the change the forward reaction will be favoured as there are fewer molecules of gas.