AQA GCSE CHEMISTRY - PAPER 2 ASSESMENT
EXAMS WITH CORRECT QUESTIONS AND
ANSWERS,
Mean rate of reaction (with reactant) - CORRECT ANSWERS✔️✔️Rate of reaction:
Quantity of reactant used
----------------------------
Time taken
Mean rate of reaction (with product) - CORRECT ANSWERS✔️✔️Rate of reaction:
Quantity of product formed
----------------------------
Time taken
Measurements for quantity of product or reactant - CORRECT ANSWERS✔️✔️Either as mass in g or as
volume in cm³
Measurements for the rate of reaction - CORRECT ANSWERS✔️✔️Either as g/s, cm³/s, or mol/s
Factors which affect rate of chemical reaction - CORRECT ANSWERS✔️✔️- *Temperature*: a faster
temperature means faster reaction
- *Concentration / pressure*: a higher concentration or pressure means a faster reaction
- *Surface area*: a larger surface area: volume ratio means a faster reaction
- *Catalysts*: a reaction in the presence of a catalyst is faster
,Collision theory - CORRECT ANSWERS✔️✔️This states that a chemical reaction can only happen when
reacting particles collide with each other with enough energy.
Activation energy - CORRECT ANSWERS✔️✔️This is the minimum energy required for a reaction to take
place.
How surface area, concentration or pressure changes rate of reaction in terms of collision theory -
CORRECT ANSWERS✔️✔️This increases the frequency of collisions, as there are more particles that are
able to collide, increasing rate of reaction.
How temperature changes rate of reaction in terms of collision theory - CORRECT ANSWERS✔️✔T️ his
increases the frequency of collisions as well as the energy the collisions have, increasing rate of reaction.
Catalysts - CORRECT ANSWERS✔️✔️- A catalyst is a substance that changes the rate of reaction
- It is not used up during the reaction, and therefore does not show up in the products or reactants
- Different reactions require different catalysts, for example an enzyme
- The catalyst does this by supplying a different pathway to the reaction that requires a lower activation
energy, shown in the picture
Reversible reactions - CORRECT ANSWERS✔️✔T️ his is a reaction in which the products can react to
produce the original reactants
A+B⇌C+D
Example of a reversible reaction - CORRECT ANSWERS✔️✔️This reaction is reversible, meaning the
reactants can be heated to get the products as well as the products can be cooled to get the reactants:
Ammonium chloride ⇌ ammonia + hydrogen chloride
Energy changes in reversible reactions - CORRECT ANSWERS✔️✔️If a reaction is endothermic in one
direction, it is exothermic in the other. The same amount of energy is transferred each way.
,Equilibrium in a reversible reaction - CORRECT ANSWERS✔️✔️If the apparatus are set up to prevent the
escape of reactants or products, an equilibrium can be reached, in which the rate of forward and reverse
reactions are the same. This will always occur in consistent conditions.
The effect of changing concentration in a reversible reaction - CORRECT ANSWERS✔️✔️When the
concentration of one product or reactant is changed, the system is no longer at equilibrium:
- If the concentration of the reactants is increased, more products are formed until a balance is reached
- If the concentration of the products is increased, more reactants will form until a balance is reached
The effect of increasing temperature in a reversible reaction - CORRECT ANSWERS✔️✔️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 - CORRECT ANSWERS✔️✔️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 - CORRECT ANSWERS✔️✔️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 - CORRECT ANSWERS✔️✔️A hydrocarbon is a material that contains only carbon and
hydrogen atoms.
Alkanes - CORRECT ANSWERS✔️✔-️ 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 - CORRECT ANSWERS✔️✔C
️ n H2n+2
The first four alkanes - CORRECT ANSWERS✔️✔️- Methane
- Ethane
- Propane
- Butane
Formula for methane - CORRECT ANSWERS✔️✔️CH₄
Formula for ethane - CORRECT ANSWERS✔️✔️C₂H₆
Formula for propane - CORRECT ANSWERS✔️✔C
️ ₃H₈
Formula for butane - CORRECT ANSWERS✔️✔️C₄H₁₀
Crude oil - CORRECT ANSWERS✔️✔️- 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 - CORRECT ANSWERS✔️✔️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.
EXAMS WITH CORRECT QUESTIONS AND
ANSWERS,
Mean rate of reaction (with reactant) - CORRECT ANSWERS✔️✔️Rate of reaction:
Quantity of reactant used
----------------------------
Time taken
Mean rate of reaction (with product) - CORRECT ANSWERS✔️✔️Rate of reaction:
Quantity of product formed
----------------------------
Time taken
Measurements for quantity of product or reactant - CORRECT ANSWERS✔️✔️Either as mass in g or as
volume in cm³
Measurements for the rate of reaction - CORRECT ANSWERS✔️✔️Either as g/s, cm³/s, or mol/s
Factors which affect rate of chemical reaction - CORRECT ANSWERS✔️✔️- *Temperature*: a faster
temperature means faster reaction
- *Concentration / pressure*: a higher concentration or pressure means a faster reaction
- *Surface area*: a larger surface area: volume ratio means a faster reaction
- *Catalysts*: a reaction in the presence of a catalyst is faster
,Collision theory - CORRECT ANSWERS✔️✔️This states that a chemical reaction can only happen when
reacting particles collide with each other with enough energy.
Activation energy - CORRECT ANSWERS✔️✔️This is the minimum energy required for a reaction to take
place.
How surface area, concentration or pressure changes rate of reaction in terms of collision theory -
CORRECT ANSWERS✔️✔️This increases the frequency of collisions, as there are more particles that are
able to collide, increasing rate of reaction.
How temperature changes rate of reaction in terms of collision theory - CORRECT ANSWERS✔️✔T️ his
increases the frequency of collisions as well as the energy the collisions have, increasing rate of reaction.
Catalysts - CORRECT ANSWERS✔️✔️- A catalyst is a substance that changes the rate of reaction
- It is not used up during the reaction, and therefore does not show up in the products or reactants
- Different reactions require different catalysts, for example an enzyme
- The catalyst does this by supplying a different pathway to the reaction that requires a lower activation
energy, shown in the picture
Reversible reactions - CORRECT ANSWERS✔️✔T️ his is a reaction in which the products can react to
produce the original reactants
A+B⇌C+D
Example of a reversible reaction - CORRECT ANSWERS✔️✔️This reaction is reversible, meaning the
reactants can be heated to get the products as well as the products can be cooled to get the reactants:
Ammonium chloride ⇌ ammonia + hydrogen chloride
Energy changes in reversible reactions - CORRECT ANSWERS✔️✔️If a reaction is endothermic in one
direction, it is exothermic in the other. The same amount of energy is transferred each way.
,Equilibrium in a reversible reaction - CORRECT ANSWERS✔️✔️If the apparatus are set up to prevent the
escape of reactants or products, an equilibrium can be reached, in which the rate of forward and reverse
reactions are the same. This will always occur in consistent conditions.
The effect of changing concentration in a reversible reaction - CORRECT ANSWERS✔️✔️When the
concentration of one product or reactant is changed, the system is no longer at equilibrium:
- If the concentration of the reactants is increased, more products are formed until a balance is reached
- If the concentration of the products is increased, more reactants will form until a balance is reached
The effect of increasing temperature in a reversible reaction - CORRECT ANSWERS✔️✔️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 - CORRECT ANSWERS✔️✔️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 - CORRECT ANSWERS✔️✔️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 - CORRECT ANSWERS✔️✔️A hydrocarbon is a material that contains only carbon and
hydrogen atoms.
Alkanes - CORRECT ANSWERS✔️✔-️ 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 - CORRECT ANSWERS✔️✔C
️ n H2n+2
The first four alkanes - CORRECT ANSWERS✔️✔️- Methane
- Ethane
- Propane
- Butane
Formula for methane - CORRECT ANSWERS✔️✔️CH₄
Formula for ethane - CORRECT ANSWERS✔️✔️C₂H₆
Formula for propane - CORRECT ANSWERS✔️✔C
️ ₃H₈
Formula for butane - CORRECT ANSWERS✔️✔️C₄H₁₀
Crude oil - CORRECT ANSWERS✔️✔️- 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 - CORRECT ANSWERS✔️✔️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.
