AQA GCSE Chemistry - Paper 2 questions and
solutions
Mean rate of reaction (with reactant) - answersRate of reaction:
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Quantity of reactant used wu wu wu
----------------------------
Time taken wu
Mean rate of reaction (with product) - answersRate of reaction:
wu wu wu wu wu wu wu wu wu
Quantity of product formed wu wu wu
----------------------------
Time taken wu
Measurements for quantity of product or reactant - answersEither as mass in g or as volume in cm³ wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
Measurements for the rate of reaction - answersEither as g/s, cm³/s, or mol/s wu wu wu wu wu wu wu wu wu wu wu wu
Factors which affect rate of chemical reaction - answers- *Temperature*: a faster temperature means faster
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reaction
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- *Concentration / pressure*: a higher concentration or pressure means a faster reaction
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- *Surface area*: a larger surface area: volume ratio means a faster reaction
wu wu wu wu wu wu wu wu wu wu wu wu
- *Catalysts*: a reaction in the presence of a catalyst is faster
wu wu wu wu wu wu wu wu wu wu wu
Collision theory - answersThis states that a chemical reaction can only happen when reacting particles collide
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with each other with enough energy.
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Activation energy - answersThis is the minimum energy required for a reaction to take place.
wu wu wu wu wu wu wu wu wu wu wu wu wu wu
How surface area, concentration or pressure changes rate of reaction in terms of collision theory - answersThis
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increases the frequency of collisions, as there are more particles that are able to collide, increasing rate of
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reaction.
wu
How temperature changes rate of reaction in terms of collision theory - answersThis increases the frequency of
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collisions as well as the energy the collisions have, increasing rate of reaction.
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Catalysts - answers- A catalyst is a substance that changes the rate of reaction
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- It is not used up during the reaction, and therefore does not show up in the products or reactants
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- Different reactions require different catalysts, for example an enzyme
wu wu wu wu wu wu wu wu wu
- The catalyst does this by supplying a different pathway to the reaction that requires a lower activation energy,
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shown in the picture
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Reversible reactions - answersThis is a reaction in which the products can react to produce the original reactants
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
,A+B⇌C+D wu wu wu wu wu wu
Example of a reversible reaction - answersThis reaction is reversible, meaning the reactants can be heated to get
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the products as well as the products can be cooled to get the reactants:
wu wu wu wu wu wu wu wu wu wu wu wu wu wu
Ammonium chloride ⇌ ammonia + hydrogen chloride wu wu wu wu wu wu
Energy changes in reversible reactions - answersIf a reaction is endothermic in one direction, it is exothermic in
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
the other. The same amount of energy is transferred each way.
wu wu wu wu wu wu wu wu wu wu wu
Equilibrium in a reversible reaction - answersIf the apparatus are set up to prevent the escape of reactants or
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
products, an equilibrium can be reached, in which the rate of forward and reverse reactions are the same. This will
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
always occur in consistent conditions.
wu wu wu wu wu
The effect of changing concentration in a reversible reaction - answersWhen the concentration of one product or
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
reactant is changed, the system is no longer at equilibrium:
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- If the concentration of the reactants is increased, more products are formed until a balance is reached
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
- If the concentration of the products is increased, more reactants will form until a balance is reached
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
The effect of increasing temperature in a reversible reaction - answersWhen the temperature is *increased*:
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- More product is formed for an endothermic reaction
wu wu wu wu wu wu wu wu
- Less product is formed for an exothermic reaction
wu wu wu wu wu wu wu wu
The effect of decreasing temperature in a reversible reaction - answersWhen the temperature is *decreased*:
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- Less product is formed for an endothermic reaction
wu wu wu wu wu wu wu wu
- More product is formed for an exothermic reaction
wu wu wu wu wu wu wu wu
The effect of changing pressure in a reversible reaction - answersFor a gaseous reaction at equilibrium:
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
- An increase in pressure causes the equilibrium position to shift towards the side of the smaller number of moles,
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meaning whichever side has less moles, more of it will be formed
wu wu wu wu wu wu wu wu wu wu wu wu
- A decrease in pressure causes the equilibrium position to shift towards the side with more moles, meaning
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
whichever side has more moles, more of it will be formed
wu wu wu wu wu wu wu wu wu wu wu
Hydrocarbon - answersA hydrocarbon is a material that contains only carbon and hydrogen atoms. wu wu wu wu wu wu wu wu wu wu wu wu wu
Alkanes - answers- These are saturated, meaning there are only single bonds between atoms
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- They are relatively unreactive, although they do combust
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- Their single bonds are quite strong
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- They are a homologous series of hydrocarbons (organic compounds with the same functional group and similar
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
chemical properties)
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- There are trends in their physical properties
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Formula for alkanes - answersCn H2n+2 wu wu wu wu wu
The first four alkanes - answers- Methane
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- Ethane
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- Propane
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- Butane
wu
, Formula for methane - answersCH₄ wu wu wu wu
Formula for ethane - answersC₂H₆ wu wu wu wu
Formula for propane - answersC₃H₈ wu wu wu wu
Formula for butane - answersC₄H₁₀ wu wu wu wu
Crude oil - answers- A finite resource found in rocks
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- Mostly ancient biomass, e.g. plankton, which has been buried in mud
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- It is a mixture of many compounds, mostly hydrocarbons, which are mostly alkanes
wu wu wu wu wu wu wu wu wu wu wu wu wu
- They are separated by fractional distillation
wu wu wu wu wu wu
Why fractional distillation works - answersThe hydrocarbons in crude oil can be separated into fractions, which
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
are chemicals that have a similar boiling point. These are molecules with a similar number of carbon atoms. Each
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
fraction has different properties and uses, a lot of which are processed to produce fuels and feedstock for the
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
petrochemical industry, e.g. petrol, kerosene, heavy fuel oil and liquefied petroleum gases.
wu wu wu wu wu wu wu wu wu wu wu wu
Process of fractional distillation - answers1. Oil is firstly heated so it turns into a gas and evaporates
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
2. It is piped to the bottom of the column
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3. The gas rises up the column and it gradually cools
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4. Different compounds in the mixture have different condensation points, so they turn back into a liquid at different
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
places in the column
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Properties of molecules at the top of the column - answers- Small wu wu wu wu wu wu wu wu wu wu wu
- Low boiling point
wu wu wu
- Very volatile (easily evaporated)
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- Flows easily
wu wu
- Ignites easily
wu wu
Properties of the molecules at the bottom - answers- Large wu wu wu wu wu wu wu wu wu
- High boiling point
wu wu wu
- Not very volatile
wu wu wu
- Does not flow easily
wu wu wu wu
- Does not ignite easily
wu wu wu wu
Products of fractional distillation (from bottom upwards) - answers- *Bitumen*: used in roads and roofs
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- *Heavy fuel oil*: used as a fuel for ships and power stations
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- *Diesel*: used as a fuel for some cars and trains
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- *Kerosene*: used as a fuel for aircraft
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- *Petrol*: used as a fuel for cars
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- *Liquified petroleum gases*: used in domestic heating and cooking
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Trends in physical properties of hydrocarbons - answers- The shorter the molecule, the *less viscous* (thick,
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
sticky) it is
wu wu wu
- The shorter the molecule, the *lower the boiling point*
wu wu wu wu wu wu wu wu wu
solutions
Mean rate of reaction (with reactant) - answersRate of reaction:
wu wu wu wu wu wu wu wu wu
Quantity of reactant used wu wu wu
----------------------------
Time taken wu
Mean rate of reaction (with product) - answersRate of reaction:
wu wu wu wu wu wu wu wu wu
Quantity of product formed wu wu wu
----------------------------
Time taken wu
Measurements for quantity of product or reactant - answersEither as mass in g or as volume in cm³ wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
Measurements for the rate of reaction - answersEither as g/s, cm³/s, or mol/s wu wu wu wu wu wu wu wu wu wu wu wu
Factors which affect rate of chemical reaction - answers- *Temperature*: a faster temperature means faster
wu wu wu wu wu wu wu wu wu wu wu wu wu wu
reaction
wu
- *Concentration / pressure*: a higher concentration or pressure means a faster reaction
wu wu wu wu wu wu wu wu wu wu wu wu
- *Surface area*: a larger surface area: volume ratio means a faster reaction
wu wu wu wu wu wu wu wu wu wu wu wu
- *Catalysts*: a reaction in the presence of a catalyst is faster
wu wu wu wu wu wu wu wu wu wu wu
Collision theory - answersThis states that a chemical reaction can only happen when reacting particles collide
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
with each other with enough energy.
wu wu wu wu wu wu
Activation energy - answersThis is the minimum energy required for a reaction to take place.
wu wu wu wu wu wu wu wu wu wu wu wu wu wu
How surface area, concentration or pressure changes rate of reaction in terms of collision theory - answersThis
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
increases the frequency of collisions, as there are more particles that are able to collide, increasing rate of
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
reaction.
wu
How temperature changes rate of reaction in terms of collision theory - answersThis increases the frequency of
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
collisions as well as the energy the collisions have, increasing rate of reaction.
wu wu wu wu wu wu wu wu wu wu wu wu wu
Catalysts - answers- A catalyst is a substance that changes the rate of reaction
wu wu wu wu wu wu wu wu wu wu wu wu wu
- It is not used up during the reaction, and therefore does not show up in the products or reactants
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
- Different reactions require different catalysts, for example an enzyme
wu wu wu wu wu wu wu wu wu
- The catalyst does this by supplying a different pathway to the reaction that requires a lower activation energy,
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
shown in the picture
wu wu wu wu
Reversible reactions - answersThis is a reaction in which the products can react to produce the original reactants
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
,A+B⇌C+D wu wu wu wu wu wu
Example of a reversible reaction - answersThis reaction is reversible, meaning the reactants can be heated to get
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
the products as well as the products can be cooled to get the reactants:
wu wu wu wu wu wu wu wu wu wu wu wu wu wu
Ammonium chloride ⇌ ammonia + hydrogen chloride wu wu wu wu wu wu
Energy changes in reversible reactions - answersIf a reaction is endothermic in one direction, it is exothermic in
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
the other. The same amount of energy is transferred each way.
wu wu wu wu wu wu wu wu wu wu wu
Equilibrium in a reversible reaction - answersIf the apparatus are set up to prevent the escape of reactants or
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
products, an equilibrium can be reached, in which the rate of forward and reverse reactions are the same. This will
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
always occur in consistent conditions.
wu wu wu wu wu
The effect of changing concentration in a reversible reaction - answersWhen the concentration of one product or
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
reactant is changed, the system is no longer at equilibrium:
wu wu wu wu wu wu wu wu wu wu
- If the concentration of the reactants is increased, more products are formed until a balance is reached
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
- If the concentration of the products is increased, more reactants will form until a balance is reached
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
The effect of increasing temperature in a reversible reaction - answersWhen the temperature is *increased*:
wu wu wu wu wu wu wu wu wu wu wu wu wu wu
- More product is formed for an endothermic reaction
wu wu wu wu wu wu wu wu
- Less product is formed for an exothermic reaction
wu wu wu wu wu wu wu wu
The effect of decreasing temperature in a reversible reaction - answersWhen the temperature is *decreased*:
wu wu wu wu wu wu wu wu wu wu wu wu wu wu
- Less product is formed for an endothermic reaction
wu wu wu wu wu wu wu wu
- More product is formed for an exothermic reaction
wu wu wu wu wu wu wu wu
The effect of changing pressure in a reversible reaction - answersFor a gaseous reaction at equilibrium:
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
- An increase in pressure causes the equilibrium position to shift towards the side of the smaller number of moles,
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
meaning whichever side has less moles, more of it will be formed
wu wu wu wu wu wu wu wu wu wu wu wu
- A decrease in pressure causes the equilibrium position to shift towards the side with more moles, meaning
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
whichever side has more moles, more of it will be formed
wu wu wu wu wu wu wu wu wu wu wu
Hydrocarbon - answersA hydrocarbon is a material that contains only carbon and hydrogen atoms. wu wu wu wu wu wu wu wu wu wu wu wu wu
Alkanes - answers- These are saturated, meaning there are only single bonds between atoms
wu wu wu wu wu wu wu wu wu wu wu wu wu
- They are relatively unreactive, although they do combust
wu wu wu wu wu wu wu wu
- Their single bonds are quite strong
wu wu wu wu wu wu
- They are a homologous series of hydrocarbons (organic compounds with the same functional group and similar
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
chemical properties)
wu wu
- There are trends in their physical properties
wu wu wu wu wu wu wu
Formula for alkanes - answersCn H2n+2 wu wu wu wu wu
The first four alkanes - answers- Methane
wu wu wu wu wu wu
- Ethane
wu
- Propane
wu
- Butane
wu
, Formula for methane - answersCH₄ wu wu wu wu
Formula for ethane - answersC₂H₆ wu wu wu wu
Formula for propane - answersC₃H₈ wu wu wu wu
Formula for butane - answersC₄H₁₀ wu wu wu wu
Crude oil - answers- A finite resource found in rocks
wu wu wu wu wu wu wu wu wu
- Mostly ancient biomass, e.g. plankton, which has been buried in mud
wu wu wu wu wu wu wu wu wu wu wu
- It is a mixture of many compounds, mostly hydrocarbons, which are mostly alkanes
wu wu wu wu wu wu wu wu wu wu wu wu wu
- They are separated by fractional distillation
wu wu wu wu wu wu
Why fractional distillation works - answersThe hydrocarbons in crude oil can be separated into fractions, which
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
are chemicals that have a similar boiling point. These are molecules with a similar number of carbon atoms. Each
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
fraction has different properties and uses, a lot of which are processed to produce fuels and feedstock for the
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
petrochemical industry, e.g. petrol, kerosene, heavy fuel oil and liquefied petroleum gases.
wu wu wu wu wu wu wu wu wu wu wu wu
Process of fractional distillation - answers1. Oil is firstly heated so it turns into a gas and evaporates
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
2. It is piped to the bottom of the column
wu wu wu wu wu wu wu wu wu
3. The gas rises up the column and it gradually cools
wu wu wu wu wu wu wu wu wu wu
4. Different compounds in the mixture have different condensation points, so they turn back into a liquid at different
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
places in the column
wu wu wu wu
Properties of molecules at the top of the column - answers- Small wu wu wu wu wu wu wu wu wu wu wu
- Low boiling point
wu wu wu
- Very volatile (easily evaporated)
wu wu wu wu
- Flows easily
wu wu
- Ignites easily
wu wu
Properties of the molecules at the bottom - answers- Large wu wu wu wu wu wu wu wu wu
- High boiling point
wu wu wu
- Not very volatile
wu wu wu
- Does not flow easily
wu wu wu wu
- Does not ignite easily
wu wu wu wu
Products of fractional distillation (from bottom upwards) - answers- *Bitumen*: used in roads and roofs
wu wu wu wu wu wu wu wu wu wu wu wu wu wu
- *Heavy fuel oil*: used as a fuel for ships and power stations
wu wu wu wu wu wu wu wu wu wu wu wu
- *Diesel*: used as a fuel for some cars and trains
wu wu wu wu wu wu wu wu wu wu
- *Kerosene*: used as a fuel for aircraft
wu wu wu wu wu wu wu
- *Petrol*: used as a fuel for cars
wu wu wu wu wu wu wu
- *Liquified petroleum gases*: used in domestic heating and cooking
wu wu wu wu wu wu wu wu wu
Trends in physical properties of hydrocarbons - answers- The shorter the molecule, the *less viscous* (thick,
wu wu wu wu wu wu wu wu wu wu wu wu wu wu wu
sticky) it is
wu wu wu
- The shorter the molecule, the *lower the boiling point*
wu wu wu wu wu wu wu wu wu
