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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