Chem - Rates & Reactions

• What is the focus of AQA GCSE Chemistry Unit 6?

  The Rate and Extent of Chemical Change
• How do reactions vary in terms of speed?

  Some reactions, like fireworks exploding, are fast, while others, like iron rusting, occur slowly.
• What does the rate of a chemical reaction indicate?

  It indicates how quickly a product is formed or how quickly a reactant is used up.
• What must happen for a chemical reaction to occur?

  The reactant particles must collide with enough energy.
• What are successful collisions in a chemical reaction?

  Successful collisions are those that produce a chemical reaction.
• What is the formula for the mean rate of reaction?


  The mean rate of reaction is calculated as the change in quantity of reactant or product over time.
• How can the mass of a reaction mixture be measured?

  The mass can be measured at regular time intervals during the reaction.
• What units are used for measuring the mass of a reaction mixture?

  The units are g/s or g/min.
• How can the volume of a reaction mixture be measured?

  The volume can be measured by collecting gas produced at regular time intervals.
• What units are used for measuring the volume of a reaction mixture?

  The units are cm³/s or cm³/min.
• What factors affect the rate of a chemical reaction?

  • Concentration and pressure
  • Catalyst
  • Surface area
  • Temperature
• How does increasing concentration or pressure affect the rate of reaction?

  It increases the rate of reaction by providing more frequent successful collisions between reactant particles.

  
• What is a catalyst?


  A catalyst is a substance that speeds up a chemical reaction without being used up itself.
• How do catalysts affect activation energy?

  Catalysts provide an alternative pathway at a lower activation energy.
• What are biological catalysts called?


  Enzymes.
• What happens to the frequency of collisions when a catalyst is used?

  The frequency of collisions remains unchanged, but more particles are able to react.
• How does temperature affect the rate of reaction?

  Increasing temperature gives reactant particles more kinetic energy, leading to more frequent successful collisions.
• How does surface area affect the rate of reaction?

  Increasing the surface area increases the frequency of successful collisions, thus increasing the rate of reaction.
• What is the formula for calculating the gradient of a graph?

  The gradient is calculated as the change in y divided by the change in x.
• What is the Haber process?

  The Haber process is an industrial process that produces ammonia from nitrogen and hydrogen under high temperature and pressure with an iron catalyst.
• What is the symbol equation for the Haber process?


  N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
• What does Le Chatelier’s Principle state?

  It states that the position of equilibrium can be altered by changing the conditions of the reaction.
• What happens to the equilibrium position if the temperature is increased in an exothermic reaction?

  The equilibrium shifts in favor of the reverse direction (endothermic) to reduce the temperature.
• How does changing pressure affect the equilibrium position?

  Increasing pressure shifts the equilibrium position to the side with fewer molecules, while decreasing pressure shifts it to the side with more molecules.

  
• What happens to the equilibrium position if the concentration of reactants is increased?

  The equilibrium position shifts in favor of the products, resulting in more product being produced.
• What is dynamic equilibrium?

  • It occurs in a closed system.
  • The forward and reverse reactions happen at the same rate.
  • The concentrations of all substances remain constant.
• How can the rate of reaction be calculated from a graph?

  By drawing construction lines on the straightest part of the graph and measuring the values of x and y.
• What is the rate of reaction at 20 seconds if 54 cm³ of gas is produced?


  $2.7 \text{ cm}^3/\text{s}$
• What is the rate of reaction at 40 seconds if 52 cm³ of gas is produced?


  $1.3 \text{ cm}^3/\text{s}$
• What is a reversible reaction?

  A reversible reaction is one where reactants form products, which can then react to reform the reactants.
• What does the double arrow symbol represent in a chemical equation?

  The double arrow symbol indicates that a reversible reaction is taking place.
• What happens to hydrated copper sulfate when heated?

  It loses water and becomes anhydrous copper sulfate, which is white.
• What is the word equation for the reaction of hydrated copper sulfate?

  Hydrated copper sulfate ⇌ Anhydrous copper sulfate + Water.
• What is the symbol equation for the reaction of hydrated copper sulfate?

  CuSO₄.5H₂O(s) ⇌ CuSO₄(s) + H₂O(l)
• What is the method for measuring the production of a gas in a reaction?

  1. Clamp a gas syringe to a retort stand.
  2. Measure hydrochloric acid and calcium carbonate.
  3. Connect the bung and delivery tube.
  4. Record the volume of gas produced at intervals.

  
• What is the method for investigating a change in color in a reaction?

  1. Place a black cross on a white tile.
  2. Measure sodium thiosulfate and hydrochloric acid.
  3. Start the stopwatch when mixed.
  4. Stop when the cross is no longer visible.

  
• How can the results from the practical investigation be analyzed?

  By plotting a graph of Time (s) against Volume of Gas Produced (cm³) and drawing a curve of best fit.
• How do you calculate the mean rate of reaction for each concentration of acid used?

  By dividing the total volume of gas produced (cm³) by the reaction time (s).
• What temperatures can be used in the investigation with sodium thiosulfate?

  Ice cold, room temperature, and hot.
• What is the purpose of the black cross in the sodium thiosulfate experiment?

  It serves as a marker to determine when the reaction has finished by observing when it is no longer visible.