AQA GCSE Combined Science Chemistry - Paper 2 Already Graded A+

AQA GCSE Combined Science Chemistry - Paper 2 Already Graded A+ 1. What is the rate of a chemical reaction? Answer: The rate of a chemical reaction is the speed at which reactants are converted into products. 2. What are some examples of chemical reactions with different rates? Answer: Examples of chemical reactions with different rates include rusting of iron (slowest), chemical weathering like acid rain damage (slow), metal magnesium reacting with acid to produce steam bubbles (moderate), burning (fast), and explosions (fastest). 3. How can you measure the speed of a reaction? Answer: You can measure the speed of a reaction by recording the amount of product formed or the amount of reactant used up over time. 4. What do rate of reaction graphs show? Answer: Rate of reaction graphs show how the amount of product formed or reactant used up changes over time, and how this changes with different conditions such as temperature, concentration, and surface area. 5. What do steep and shallow lines on a rate of reaction graph indicate? Answer: Steep lines on a rate of reaction graph indicate a faster rate of reaction, while shallow lines indicate a slower rate. 6. What does a flat line on a rate of reaction graph indicate? Answer: A flat line on a rate of reaction graph indicates that the reaction has finished. 7. What do higher lines on a rate of reaction graph indicate? Answer: Higher lines on a rate of reaction graph indicate more reactants and products. 8. What is collision theory in relation to rate of reaction? Answer: Collision theory states that the frequency and energy of collisions between reacting particles affect the rate of reaction. 9. What is activation energy in relation to rate of reaction? Answer: Activation energy is the minimum amount of energy needed for reactants to break bonds and start a reaction. 10. What are some factors that affect the rate of reaction? Answer: Factors that affect the rate of reaction include temperature, concentration, pressure, and surface area. 11. What is a catalyst in relation to rate of reaction? Answer: A catalyst is a substance that speeds up the rate of reaction without being used up itself. 12. How do catalysts increase the rate of reaction? Answer: Catalysts increase the rate of reaction by providing an alternative pathway with lower activation energy, allowing reactants to convert into products more easily. 13. How is the rate of reaction measured in precipitation and colour change reactions? Answer: The rate of reaction can be measured by observing how long it takes for a solution to lose or gain color, become cloudy or transparent, or for a mark to disappear. Measuring rate of reaction - Change in mass ️- Put reaction on a measuring scale - If a gas is produced, the mass will decrease - The quicker the mass decreases, the faster the reaction Measuring rate of reaction - Volume of gas given off ️- A gas syringe is used to measure vol of gas being produced - The more gas given off in a given time interval = faster rate Magnesium and HCl react to produce H2 gas ️1. Add a set volume of dilute HCL to a conical flask and place on mass balance. 2. Add a magnesium ribbon to acid and quickly plug the flask with cotton wool. 3. Start stopwatch and record mass of balance at regular intervals. 4. Plot results in a table and work out mass lost for each reading -> plot results on a graph. 5. Repeat with more concentrated acid solutions. (Keep control variables like volume of acid and amount of magnesium ribbon same each time) Sodium Thiosulfate and HCL produces a Cloudy Precipitate ️1. Both chemicals are clear solutions.= they react together to form a yellow precipitate of sulfur. 2. Add a set volume of dilute sodium thiosulfate to a conical flask. 3. Place flask on piece of paper with a cross drawn on it. Add dilute GCL to flask and start the stopwatch. 4. Time how long it takes for the mark to disappear through the cloudy sulfur. 5. Repeat with different concentrations of one reactant. As the concentration increases the time taken for mark to disapper decreases. Finding reaction rates from graphs ️1. Calculating mean rate - overall change in y axis / total time taken 2. Calculating rate at a point - draw a tangent at the point and find the gradient Reversible reaction ️A + B ↔ C + D Rate of reversible reactions ️- As reactants react, their concentration falls (forward reaction slows down) but as products are made, their concentration rises (backward reaction will speed up) - Eventually forward reaction will be going at the same rate as the backward reaction (equilibrium) Equilibrium in Reversible reactions ️- At equilibrium both reactions are still happening but no overall effect - this means hat concentrations of reactants and products have reached a balance and will not change. - Equiliibrium is only reached if the reversible reaction takes place in a 'closed system' (none of the reactants or products can escaped nothing can get in). Position of Equilibrium ️- Equilibrium doesn't mean amounts of reactants and products are equal - If Equilibrium lies to right = higher conc. of products - If Equilibrium lies to left = higher conc. of reactants Position of equilibrium depends on - Temperature - Pressure - Concentration Conditions affecting Position of Equilibrium ️Position of equilibrium depends on - Temperature (HEAT = right , COOL = left) - Pressure (only for gases) - Concentration (of reactants and products) Exothermic and Endothermic Reversible Reactions ️- if endothermic in one direction, exothermic in other - Energy transferred from surroundings = energy transferred to surroundings Le Chatelier's Principle ️If you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change - can be used to predict the effect of any change you make to a reaction system. Le Chatelier's Principle - Changes to Temperature ️1. If you decrease the temperature = the equilibrium will move in the exothermic direction to produce more heat = more products for the exothermic reaction than the endothermic reaction. 2. If you increase the temperature = the equilibrium will move in the endothermic direction to try & decrease it = more products for the endothermic reaction than the exothermic reaction. Le Chatelier's Principle - Changes to Pressure ️1. Changing pressure