exothermic and endothermic

• What is the method used to determine changes in heat content in reactions?

  A thermometer
• What does the law of conservation of energy state?


  Energy cannot be created or destroyed, only transferred
• If energy is transferred to the surroundings during a chemical reaction, what can be inferred about the products formed?


  The products have less energy than the reactants
• What are examples of physical processes that involve heat exchange?

  • Freezing
  • Melting
• What is an exothermic reaction?


  An exothermic reaction releases heat energy
• What happens to the temperature during an exothermic reaction?


  The temperature increases
• Give two examples of exothermic reactions.


  Neutralisation and combustion
• What is an endothermic reaction?


  An endothermic reaction takes in heat energy
• What happens to the temperature during an endothermic reaction?


  The temperature decreases
• Name two typical endothermic reactions.

  Electrolysis and thermal decomposition
• How are cold packs used in sports injury treatment related to endothermic reactions?


  They absorb heat from the injured area to prevent swelling
• What are the key differences between exothermic and endothermic reactions?


  • Exothermic: Releases heat, temperature of surroundings increases
  • Endothermic: Absorbs heat, temperature of surroundings decreases
• What is the objective of the calorimetry study involving HCl and NaOH?


  To investigate temperature changes during the reaction
• What hypothesis is proposed for the calorimetry study?


  The temperature change will vary depending on the amounts of solutions involved
• What materials are needed for the calorimetry study?


  Dilute hydrochloric acid and dilute sodium hydroxide solution
• What is the first step in the calorimetry method?


  Place 25 cm³ of the NaOH solution into the calorimeter
• What should be done after adding HCl to the NaOH solution in the calorimetry study?


  Stir the mixture and measure the highest temperature reached
• What is the relationship between temperature change and energy in the calorimetry study?


  • Larger temperature difference indicates more energy absorbed or released
• What is activation energy in a chemical reaction?


  The minimum amount of energy required for a collision to be successful
• What factors influence the success of collisions in chemical reactions?


  Energy, orientation, and number of collisions per second
• How do activation energies differ among reactions?


  Higher activation energies require more energy to start than lower ones
• What do energy profile diagrams represent?


  • Relative energies of reactants and products
  • Y-axis: Energy
  • X-axis: Progress of the reaction
• How is the energy change represented in an exothermic reaction on an energy profile diagram?


  With a downward arrow indicating energy is given out
• How is the energy change represented in an endothermic reaction on an energy profile diagram?


  With an upward arrow indicating energy is taken in
• What is the difference between bond breaking and bond making in terms of energy?


  • Bond breaking: Endothermic, energy absorbed
  • Bond making: Exothermic, energy released
• What determines whether a reaction is endothermic or exothermic?


  The difference between energy needed to break bonds and energy released when new bonds are formed
• What is the energy change in an endothermic reaction?


  Positive, since products have more energy than reactants
• What is the energy change in an exothermic reaction?


  Negative, since products have less energy than reactants
• How can bond energy calculations be used in reactions?


  • Calculate heat released or absorbed
  • Use bond energies of reactants and products
• How do you calculate the energy change for a reaction?


  Energy change = Energy taken in - Energy given out
• In the reaction of hydrogen and chlorine to form hydrogen chloride, what is the energy in?


  678 kJ
• In the reaction of hydrogen and chlorine to form hydrogen chloride, what is the energy out?


  862 kJ
• What is the overall energy change for the reaction of hydrogen and chlorine to form hydrogen chloride?


  • 184 kJ
• Why is the reaction of hydrogen and chlorine to form hydrogen chloride classified as exothermic?


  Because the energy change is negative, indicating energy is released
• In the reaction of hydrogen with iodine to form hydrogen iodide, what is the energy in?


  587 kJ
• In the reaction of hydrogen with iodine to form hydrogen iodide, what is the energy out?


  590 kJ
• What is the overall energy change for the reaction of hydrogen with iodine to form hydrogen iodide?


  • 3 kJ
• Why is the reaction of hydrogen with iodine to form hydrogen iodide classified as exothermic?


  Because more energy is released than taken in
• In the decomposition of hydrogen bromide, what is the energy in?


  732 kJ
• What is the overall energy change for the decomposition of hydrogen bromide?


  +103 kJ