AQA GCSE Chemistry - Paper 2 Verified Solutions
1. What is the formula for calculating the mean rate of reaction?
Answer: Rate of reaction = Quantity of reactant used / Time taken
2. How do you calculate the mean rate of reaction using the product?
Answer: Rate of reaction = Quantity of product formed / Time taken
3. What are the typical units for measuring quantities of reactants or products?
Answer: Mass in grams (g) or volume in cubic centimeters (cm³)
4. What are the typical units for measuring the rate of reaction?
Answer: Either grams per second (g/s), cubic centimeters per second (cm³/s), or moles per second
(mol/s)
5. What are the key factors that can affect the rate of a chemical reaction?
Answer: Temperature, concentration or pressure, surface area, and catalysts
6. According to collision theory, what is necessary for a chemical reaction to occur?
Answer: A collision between particles with sufficient energy
7. How do changes in surface area, concentration, or pressure impact the rate of reaction according to
collision theory?
,Answer: By increasing the frequency of collisions, allowing more particles to interact and react
8. How does temperature influence the rate of reaction according to collision theory?
Answer: By increasing both the frequency and energy of collisions, leading to a faster reaction
9. What is a catalyst, and what role does it play in a chemical reaction?
Answer: A catalyst is a substance that speeds up a reaction without being consumed; it provides an
alternative pathway with lower activation energy
10. What is an example of a reversible reaction?
Answer: The reaction between ammonium chloride, ammonia, and hydrogen chloride
11. What happens to energy during a reversible reaction?
Answer: The same amount of energy is transferred in both directions; if one direction is endothermic,
the other is exothermic
12. How does equilibrium occur in a reversible reaction?
Answer: When the rates of forward and reverse reactions become equal, preventing further changes in
concentration
13. What happens when you change the concentration of reactants or products in a reversible reaction?
Answer: The system moves towards equilibrium as more reactants form products or vice versa until
balance is reached
The effect of increasing temperature in a reversible reaction ✔️When the temperature is *increased*:
,- More product is formed for an endothermic reaction
- Less product is formed for an exothermic reaction
The effect of decreasing temperature in a reversible reaction ✔️When the temperature is *decreased*:
- Less product is formed for an endothermic reaction
- More product is formed for an exothermic reaction
The effect of changing pressure in a reversible reaction ✔️For a gaseous reaction at equilibrium:
- An increase in pressure causes the equilibrium position to shift towards the side of the smaller number
of moles, meaning whichever side has less moles, more of it will be formed
- A decrease in pressure causes the equilibrium position to shift towards the side with more moles,
meaning whichever side has more moles, more of it will be formed
Hydrocarbon ✔️A hydrocarbon is a material that contains only carbon and hydrogen atoms.
Alkanes ✔️- These are saturated, meaning there are only single bonds between atoms
- They are relatively unreactive, although they do combust
- Their single bonds are quite strong
- They are a homologous series of hydrocarbons (organic compounds with the same functional group
and similar chemical properties)
- There are trends in their physical properties
Formula for alkanes ✔️Cn H2n+2
The first four alkanes ✔️- Methane
- Ethane
- Propane
- Butane
, Formula for methane ✔️CH₄
Formula for ethane ✔️C₂H₆
Formula for propane ✔️C₃H₈
Formula for butane ✔️C₄H₁₀
Crude oil ✔️- A finite resource found in rocks
- Mostly ancient biomass, e.g. plankton, which has been buried in mud
- It is a mixture of many compounds, mostly hydrocarbons, which are mostly alkanes
- They are separated by fractional distillation
Why fractional distillation works ✔️The hydrocarbons in crude oil can be separated into fractions,
which are chemicals that have a similar boiling point. These are molecules with a similar number of
carbon atoms. Each fraction has different properties and uses, a lot of which are processed to produce
fuels and feedstock for the petrochemical industry, e.g. petrol, kerosene, heavy fuel oil and liquefied
petroleum gases.
Process of fractional distillation ✔️1. Oil is firstly heated so it turns into a gas and evaporates
2. It is piped to the bottom of the column
3. The gas rises up the column and it gradually cools
4. Different compounds in the mixture have different condensation points, so they turn back into a
liquid at different places in the column
Properties of molecules at the top of the column ✔️- Small
- Low boiling point
1. What is the formula for calculating the mean rate of reaction?
Answer: Rate of reaction = Quantity of reactant used / Time taken
2. How do you calculate the mean rate of reaction using the product?
Answer: Rate of reaction = Quantity of product formed / Time taken
3. What are the typical units for measuring quantities of reactants or products?
Answer: Mass in grams (g) or volume in cubic centimeters (cm³)
4. What are the typical units for measuring the rate of reaction?
Answer: Either grams per second (g/s), cubic centimeters per second (cm³/s), or moles per second
(mol/s)
5. What are the key factors that can affect the rate of a chemical reaction?
Answer: Temperature, concentration or pressure, surface area, and catalysts
6. According to collision theory, what is necessary for a chemical reaction to occur?
Answer: A collision between particles with sufficient energy
7. How do changes in surface area, concentration, or pressure impact the rate of reaction according to
collision theory?
,Answer: By increasing the frequency of collisions, allowing more particles to interact and react
8. How does temperature influence the rate of reaction according to collision theory?
Answer: By increasing both the frequency and energy of collisions, leading to a faster reaction
9. What is a catalyst, and what role does it play in a chemical reaction?
Answer: A catalyst is a substance that speeds up a reaction without being consumed; it provides an
alternative pathway with lower activation energy
10. What is an example of a reversible reaction?
Answer: The reaction between ammonium chloride, ammonia, and hydrogen chloride
11. What happens to energy during a reversible reaction?
Answer: The same amount of energy is transferred in both directions; if one direction is endothermic,
the other is exothermic
12. How does equilibrium occur in a reversible reaction?
Answer: When the rates of forward and reverse reactions become equal, preventing further changes in
concentration
13. What happens when you change the concentration of reactants or products in a reversible reaction?
Answer: The system moves towards equilibrium as more reactants form products or vice versa until
balance is reached
The effect of increasing temperature in a reversible reaction ✔️When the temperature is *increased*:
,- More product is formed for an endothermic reaction
- Less product is formed for an exothermic reaction
The effect of decreasing temperature in a reversible reaction ✔️When the temperature is *decreased*:
- Less product is formed for an endothermic reaction
- More product is formed for an exothermic reaction
The effect of changing pressure in a reversible reaction ✔️For a gaseous reaction at equilibrium:
- An increase in pressure causes the equilibrium position to shift towards the side of the smaller number
of moles, meaning whichever side has less moles, more of it will be formed
- A decrease in pressure causes the equilibrium position to shift towards the side with more moles,
meaning whichever side has more moles, more of it will be formed
Hydrocarbon ✔️A hydrocarbon is a material that contains only carbon and hydrogen atoms.
Alkanes ✔️- These are saturated, meaning there are only single bonds between atoms
- They are relatively unreactive, although they do combust
- Their single bonds are quite strong
- They are a homologous series of hydrocarbons (organic compounds with the same functional group
and similar chemical properties)
- There are trends in their physical properties
Formula for alkanes ✔️Cn H2n+2
The first four alkanes ✔️- Methane
- Ethane
- Propane
- Butane
, Formula for methane ✔️CH₄
Formula for ethane ✔️C₂H₆
Formula for propane ✔️C₃H₈
Formula for butane ✔️C₄H₁₀
Crude oil ✔️- A finite resource found in rocks
- Mostly ancient biomass, e.g. plankton, which has been buried in mud
- It is a mixture of many compounds, mostly hydrocarbons, which are mostly alkanes
- They are separated by fractional distillation
Why fractional distillation works ✔️The hydrocarbons in crude oil can be separated into fractions,
which are chemicals that have a similar boiling point. These are molecules with a similar number of
carbon atoms. Each fraction has different properties and uses, a lot of which are processed to produce
fuels and feedstock for the petrochemical industry, e.g. petrol, kerosene, heavy fuel oil and liquefied
petroleum gases.
Process of fractional distillation ✔️1. Oil is firstly heated so it turns into a gas and evaporates
2. It is piped to the bottom of the column
3. The gas rises up the column and it gradually cools
4. Different compounds in the mixture have different condensation points, so they turn back into a
liquid at different places in the column
Properties of molecules at the top of the column ✔️- Small
- Low boiling point
