AQA GCSE CHEMISTRY 8462/2H Paper 2 Higher Tier
Question Paper + Mark scheme [MERGED] June
(2023/2024)(VERIFIED)
Mean rate of reaction (with reactant) - ans -Rate of reaction:
Quantity of reactant used
----------------------------
Time taken
Mean rate of reaction (with product) - ans -Rate ...
AQA GCSE CHEMISTRY 8462/2H Paper 2 Higher Tier
Question Paper + Mark scheme [MERGED] June
(2023/2024)(VERIFIED)
Mean rate of reaction (with reactant) - ans -Rate of reaction:
Quantity of reactant used
----------------------------
Time taken
Mean rate of reaction (with product) - ans -Rate of reaction:
Quantity of product formed
----------------------------
Time taken
Measurements for quantity of product or reactant - ans -Either as mass in g or as
volume in cm³
Measurements for the rate of reaction - ans -Either as g/s, cm³/s, or mol/s
Factors which affect rate of chemical reaction - ans -- *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 - ans -This states that a chemical reaction can only happen when
reacting particles collide with each other with enough energy.
Activation energy - ans -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 - ans -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 - ans -This
increases the frequency of collisions as well as the energy the collisions have,
increasing rate of reaction.
Catalysts - ans -- 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 - ans -This is a reaction in which the products can react to produce
the original reactants
A+B⇌C+D
Example of a reversible reaction - ans -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 - ans -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 - ans -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 - ans -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 - ans -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 - ans -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 - ans -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 - ans -A hydrocarbon is a material that contains only carbon and hydrogen
atoms.
Alkanes - ans -- 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 - ans -Cn H2n+2
The first four alkanes - ans -- Methane
- Ethane
- Propane
- Butane
Formula for methane - ans -CH₄
Formula for ethane - ans -C₂H₆
Formula for propane - ans -C₃H₈
Formula for butane - ans -C₄H₁₀
Crude oil - ans -- 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 - ans -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 - ans -1. Oil is firstly heated so it turns into a gas and
evaporates
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