C5 Energy changes

• What are the two types of reactions discussed in Topic 5?

  Exothermic and Endothermic reactions
• What happens to energy during chemical reactions?

  Energy is moved around, causing temperature changes.
• What does it indicate if the products of a reaction store more energy than the reactants?

  Energy was absorbed from the surroundings during the reaction.
• What is the principle of conservation of energy in chemical reactions?

  The total amount of energy remains the same; it cannot be created or destroyed, only transferred.
• What is an exothermic reaction?

  An exothermic reaction is one that releases heat to the surroundings.
• What is the best example of an exothermic reaction?

  Burning fuels, also known as combustion.
• What type of reaction is neutralization?

  Neutralization reactions are exothermic.
• What happens when sodium is added to water?

  The reaction releases energy, indicating it is exothermic.
• How do hand warmers utilize exothermic reactions?

  They use the exothermic oxidation of iron in air to release heat.
• What is an endothermic reaction?

  An endothermic reaction is one that takes in energy from the surroundings.
• What is thermal decomposition?

  It is a process where heating a compound causes it to break down into simpler substances.
• How are endothermic reactions used in sports injury packs?

  They allow the pack to become instantly cooler without needing a freezer.
• What does the prefix "exo-" and the suffix "-thermic" mean in the term exothermic?

  "Exo-" means exit, and "-thermic" means heat, indicating heat is given out.
• How can you measure the energy released by a chemical reaction?

  By measuring the temperature change of the solution before and after the reaction.
• What is a major problem when measuring energy changes in reactions?

  The amount of energy lost to the surroundings.
• How can you reduce energy loss during measurements?

  By insulating the polystyrene cup with cotton wool and covering it with a lid.
• What is the procedure to test the effect of acid concentration on energy released in a neutralization reaction?

  1. Prepare 25 mL of hydrochloric acid and sodium hydroxide in separate beakers.
  2. Place the beakers in a water bath at 25 °C.
  3. Mix them in a polystyrene cup with a lid.
  4. Measure the temperature every 30 seconds and record the highest temperature.
  5. Repeat with different concentrations of hydrochloric acid.
• What do reaction profiles show?

  They show the relative energies of reactants and products and how energy changes during the reaction.
• What does a reaction profile for an exothermic reaction indicate?

  The products are at a lower energy than the reactants, indicating energy is released.
• What is activation energy?

  It is the minimum amount of energy needed for reactants to collide and react.
• How does the activation energy affect the rate of a reaction?

  The greater the activation energy, the more energy needed to start the reaction, affecting its rate.
• What does a reaction profile for an endothermic reaction indicate?

  The products are at a higher energy than the reactants, indicating energy is absorbed.
• What is bond breaking and how is it classified?

  Bond breaking requires energy and is classified as endothermic.
• What is bond formation and how is it classified?

  Bond formation releases energy and is classified as exothermic.
• How do bond energies relate to energy changes in reactions?

  • Energy is required to break bonds (endothermic).
  • Energy is released when new bonds are formed (exothermic).
  • Overall energy change = energy required to break bonds - energy released by forming bonds.
• How do you calculate the overall energy change for a reaction?

  By subtracting the energy released by forming bonds from the energy required to break bonds.
• What is the significance of knowing bond energies in chemical reactions?

  • Helps calculate energy changes in reactions.
  • Allows comparison of energy changes between different reactions.
  • Essential for understanding reaction mechanisms and thermodynamics.
• What is the energy change for breaking bonds in a chemical reaction?

  Energy is absorbed
• Why can't you compare the energy changes of reactions without knowing bond energies?

  Because you need to know the asymmetrical differences in the bond energies.
• Which bonds are weaker: Br-Br or Cl-Cl bonds?

  Br-Br bonds are weaker than Cl-Cl bonds.
• Why can't you determine which reaction releases more energy without knowing specific bond energy differences?

  Because the energy released when new bonds form varies based on the exact differences in bond energies.
• What is an electrochemical cell?

  • A system made up of two different electrodes in contact with an electrolyte.
  • Conducts electricity through the electrodes.
• What is the role of the electrolyte in an electrochemical cell?

  The electrolyte is a liquid that contains ions which react with the electrodes.
• How does a charge difference set up in an electrochemical cell?

  Through the chemical reactions between the electrodes and the electrolyte.
• What happens when the electrodes of an electrochemical cell are connected by a wire?

  The charge is able to flow, producing electricity.
• What factors affect the voltage of a cell?

  The type of electrodes used and the difference in reactivity of the electrodes.
• How can you predict the voltage of a cell?

  From information about the voltages of other cells with similar electrodes.
• What happens to the voltage if the difference in reactivity of the electrodes increases?

  The voltage of the cell increases.
• What is a battery?

  • A battery is formed by connecting two or more cells together in series.
  • The voltages of the cells in the battery are combined for a larger overall voltage.
• What happens in non-rechargeable batteries over time?

  The reacting particles get used up and turned into the products of the reaction.