AQA GCSE Chemistry - Paper 2 Questions with Complete Solutions 2024/2025

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 .Wh