Introduction

This sample assessment focuses on Enthalpy in Reactions, an important topic in chemistry. The questions are designed to help Key Stage 3 students understand enthalpy changes in chemical reactions. The questions are organised into three levels: Easy, Medium, and Hard, so that students can progressively build their knowledge and apply it to different scenarios.

Easy Questions

  1. What is meant by “enthalpy” in chemistry?
  2. True or False: Enthalpy is a measure of heat energy in a system.
  3. What is the unit for measuring enthalpy?
  4. What does an “exothermic” reaction do with energy?
  5. What does an “endothermic” reaction do with energy?
  6. True or False: An exothermic reaction releases heat into the surroundings.
  7. Name one example of an exothermic reaction.
  8. Name one example of an endothermic reaction.
  9. What happens to the temperature of the surroundings during an exothermic reaction?
  10. What happens to the temperature of the surroundings during an endothermic reaction?
  11. True or False: Burning fuel is an example of an exothermic reaction.
  12. What is the symbol for change in enthalpy?
  13. If a reaction absorbs heat, is it exothermic or endothermic?
  14. What does it mean if the enthalpy change of a reaction is negative?
  15. What is the effect of an exothermic reaction on the surrounding temperature?
  16. True or False: Photosynthesis is an example of an exothermic reaction.
  17. What does it mean if the enthalpy change of a reaction is positive?
  18. Which type of reaction, exothermic or endothermic, requires a continuous input of energy to keep going?
  19. Name a reaction that involves an increase in enthalpy.
  20. True or False: In an endothermic reaction, energy is transferred from the surroundings to the system.

Medium Questions

  1. Explain the difference between exothermic and endothermic reactions in terms of energy transfer.
  2. How can we tell if a reaction is exothermic or endothermic based on its enthalpy change?
  3. Why does an exothermic reaction have a negative enthalpy change?
  4. Write the equation for the combustion of methane and explain why it is exothermic.
  5. In terms of energy, what happens to the bonds in the reactants during an exothermic reaction?
  6. Why does the temperature of the surroundings increase during an exothermic reaction?
  7. What happens to the energy in a chemical reaction when the products have lower enthalpy than the reactants?
  8. Describe the energy change that occurs when bonds are broken in an endothermic reaction.
  9. True or False: Bond breaking is always an endothermic process.
  10. Explain why a chemical cold pack feels cold when used.
  11. How does the enthalpy change of an exothermic reaction differ from that of an endothermic reaction?
  12. True or False: In an exothermic reaction, energy is stored in the bonds of the products.
  13. How does a change in enthalpy relate to the energy released or absorbed in a reaction?
  14. What is the role of activation energy in determining whether a reaction is exothermic or endothermic?
  15. Explain why combustion reactions are always exothermic.
  16. How does the enthalpy change during photosynthesis indicate that it is an endothermic reaction?
  17. If a chemical reaction has a positive enthalpy change, what does this tell us about the energy involved?
  18. True or False: Energy is absorbed when bonds are broken in a reaction.
  19. Describe what happens to the enthalpy during the formation of chemical bonds in an exothermic reaction.
  20. How can a calorimeter be used to measure the enthalpy change of a reaction?

Hard Questions

  1. Explain why bond breaking is endothermic and bond making is exothermic in terms of energy transfer.
  2. Compare the energy profiles of exothermic and endothermic reactions.
  3. How does the concept of enthalpy apply to the conservation of energy in chemical reactions?
  4. Describe the difference between the activation energy of exothermic and endothermic reactions.
  5. Discuss how enthalpy changes in a reaction can affect the rate at which the reaction occurs.
  6. Write the equation for the enthalpy change of a reaction and explain the meaning of each term.
  7. How does the enthalpy change of a reaction affect the equilibrium position in reversible reactions?
  8. Explain why some reactions require a catalyst to lower the activation energy, even if they are exothermic.
  9. How do changes in enthalpy influence the temperature of a reaction system at constant pressure?
  10. Describe how enthalpy changes are used to calculate the energy efficiency of fuel combustion.
  11. Why are reactions with large positive enthalpy changes typically slower than those with large negative enthalpy changes?
  12. Explain why the total enthalpy change in a reaction is the same whether the reaction occurs in one step or several steps.
  13. How does the concept of enthalpy relate to the heat of vaporisation and heat of fusion of a substance?
  14. Compare the enthalpy changes involved in the thermal decomposition of calcium carbonate with that of magnesium carbonate.
  15. Why is it important to measure the enthalpy change in industrial chemical reactions?
  16. How can Hess’s Law be used to calculate enthalpy changes in reactions where direct measurement is difficult?
  17. Discuss how changes in pressure can influence the enthalpy change of a reaction involving gases.
  18. Explain the significance of standard enthalpy changes in determining the feasibility of a chemical reaction.
  19. How does the specific heat capacity of a substance affect the enthalpy change measured in a calorimetry experiment?
  20. Why is the enthalpy change of neutralisation always exothermic, regardless of the acids or bases involved?

Answers

Easy Questions

  1. Enthalpy is the total heat content of a system, often related to the energy of a chemical reaction.
  2. True.
  3. Joules (J) or kilojoules (kJ).
  4. It releases energy.
  5. It absorbs energy.
  6. True.
  7. Combustion of fuel.
  8. Photosynthesis.
  9. The temperature increases.
  10. The temperature decreases.
  11. True.
  12. ΔH.
  13. Endothermic.
  14. It means the reaction releases energy (exothermic).
  15. It increases the surrounding temperature.
  16. False.
  17. The reaction absorbs energy (endothermic).
  18. Endothermic.
  19. Melting ice or photosynthesis.
  20. True.

Medium Questions

  1. Exothermic reactions release energy to the surroundings, while endothermic reactions absorb energy from the surroundings.
  2. If the enthalpy change is negative, the reaction is exothermic; if it is positive, the reaction is endothermic.
  3. A negative enthalpy change means that the system has lost energy by releasing it to the surroundings.
  4. CH₄ + 2O₂ → CO₂ + 2H₂O. The reaction is exothermic because it releases heat.
  5. Energy is released when the bonds in the reactants are broken and new bonds are formed in the products.
  6. Heat energy is transferred from the system to the surroundings, raising the temperature.
  7. Energy is released to the surroundings, lowering the enthalpy of the products.
  8. Energy is absorbed to break the bonds in the reactants, increasing the enthalpy of the system.
  9. True.
  10. The reaction in a chemical cold pack absorbs heat from the surroundings, making it feel cold.
  11. Exothermic reactions have a negative enthalpy change, while endothermic reactions have a positive enthalpy change.
  12. False. In an exothermic reaction, energy is released when bonds form in the products.
  13. The enthalpy change reflects the difference between the energy absorbed and released in a reaction.
  14. Activation energy is the minimum energy required to start a reaction; it determines how much energy needs to be absorbed before the reaction can proceed.
  15. Combustion reactions release heat because the reactants (like fuel and oxygen) have more energy than the products (like CO₂ and H₂O).
  16. During photosynthesis, plants absorb energy (sunlight), indicating a positive enthalpy change and an endothermic reaction.
  17. It tells us that the reaction absorbs energy from the surroundings (endothermic).
  18. True.
  19. When chemical bonds are formed, energy is released, lowering the enthalpy.
  20. A calorimeter measures the heat change in a reaction by tracking temperature changes in the reaction mixture.

Hard Questions

  1. Bond breaking requires energy to overcome the forces holding atoms together (endothermic), while bond making releases energy as new bonds form (exothermic).
  2. Exothermic reactions have an energy profile where the products are at a lower energy level than the reactants, while endothermic reactions have products at a higher energy level.
  3. Enthalpy demonstrates that energy is conserved in a reaction, either being absorbed or released, but never created or destroyed.
  4. Exothermic reactions have lower activation energy than endothermic reactions because less energy is needed to start releasing heat.
  5. Large enthalpy changes can increase the reaction rate by providing more energy to overcome activation energy, while small changes can slow the rate.
  6. ΔH = H(products) – H(reactants), where ΔH represents the enthalpy change.
  7. A reaction with a negative enthalpy change favours the formation of products, shifting the equilibrium position towards them.
  8. A catalyst lowers the activation energy, speeding up the reaction without affecting the overall enthalpy change.
  9. If enthalpy decreases, heat is released, warming the system. If enthalpy increases, heat is absorbed, cooling the system.
  10. Enthalpy changes show how much energy is released per mole of fuel, helping to calculate the energy efficiency of combustion.
  11. Reactions with positive enthalpy changes absorb energy, slowing the reaction, while negative changes release energy, speeding it up.
  12. The enthalpy change remains the same because energy is conserved regardless of the number of steps in the reaction.
  13. The heat of vaporisation and heat of fusion are both measures of the enthalpy change required to change a substance’s state.
  14. Magnesium carbonate requires more energy to decompose than calcium carbonate because of the stronger bonds in its structure.
  15. Measuring enthalpy changes ensures that reactions release or absorb the correct amount of energy, which is critical in industrial processes.
  16. Hess’s Law states that the enthalpy change of a reaction is the same, whether it takes one step or several, making it useful for calculating enthalpy changes indirectly.
  17. Changes in pressure can affect the energy required for reactions involving gases, thereby altering the enthalpy change.
  18. Standard enthalpy changes give a baseline for predicting whether a reaction will occur spontaneously under standard conditions.
  19. The specific heat capacity determines how much heat is absorbed or released per degree of temperature change, affecting the measured enthalpy change.
  20. The neutralisation of an acid and a base always releases energy because bonds form between ions, making the reaction exothermic.

This set of questions on Enthalpy in Reactions will help Key Stage 3 students build a deep understanding of how energy is involved in chemical reactions. Regular practice will reinforce their learning and improve their problem-solving skills in chemistry.