Exo endo, bond energies, batteries, fuel cells

• What are the two types of reactions discussed in the topic of energy changes?

  Exothermic and Endothermic reactions
• What happens in an exothermic reaction?

  Heat is given out
• What occurs in an endothermic reaction?

  Heat is taken in
• What is the practical method to measure energy released by a chemical reaction?

  Measure the temperature of reactants and the highest temperature after mixing
• What does a bigger rise in temperature indicate in a chemical reaction?

  More energy is released in the reaction
• How can you reduce energy loss to the surroundings during a reaction measurement?

  By putting a lid on the cup
• What variable can be investigated using the described method?

  The effect of acid concentration on the energy used
• What are the steps to test the effect of acid concentration on energy released in a neutralization reaction?

  1. Measure 25 cm³ of hydrochloric acid and sodium hydroxide in separate beakers.
  2. Place beakers in a water bath at 25 °C.
  3. Mix HCl and NaOH in a polystyrene cup with a lid.
  4. Record the temperature every 20 seconds and note the highest temperature.
  5. Repeat with different concentrations of hydrochloric acid.
• What do reaction profiles show?

  The relative energies of reactants and products and energy changes during the reaction
• In an exothermic reaction, where are the products in relation to the reactants on a reaction profile?

  The products are at a lower energy than the reactants
• What does the initial rise in energy on a reaction profile represent?

  The activation energy needed to start the reaction
• What is activation energy?

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

  The greater the activation energy, the more energy needed to start the reaction
• In an endothermic reaction, where are the products in relation to the reactants on a reaction profile?

  The products are at a higher energy than the reactants
• What does the difference in height on a reaction profile represent?

  The overall energy change during the reaction per mole
• How can energy changes in a chemical reaction be calculated?

  Using bond energies from a data book
• What is the energy change in a reaction?

  The difference between energy used to break bonds in reactants and energy released when new bonds form in products
• How do you calculate the overall energy change for a reaction?

  Overall energy change = energy required to break bonds - energy released by forming bonds
• Why can't you compare overall energy changes of reactions without knowing bond energies?

  Because the numerical differences in bond energies are necessary for comparison
• What is an electrochemical cell?

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

  It is a liquid that can conduct electricity
• What happens when the electrodes in an electrochemical cell are connected by a wire?

  The charge is able to flow and electricity is produced
• What factors affect the voltage of a cell?

  Different metals and the electrolyte used
• How can you predict the voltage of a cell?

  From information about the voltages of other cells and different electrodes
• What happens in non-rechargeable batteries over time?

  The reacting particles get used up and turned into products
• Why can't non-rechargeable batteries be recharged?

  The products can't be turned back into reactants
• What is a fuel cell?

  A type of cell that uses a continuous supply of fuel and oxygen to produce electricity
• What are the products of a hydrogen-oxygen fuel cell reaction?

  Harmless gases or water
• Why are fuel cell vehicles becoming more popular?

  They produce fewer pollutants than conventional fuels
• What is a disadvantage of using hydrogen fuel cells?

  Hydrogen is explosive when mixed with air
• How is hydrogen fuel often produced?

  From hydrocarbons or by electrolysis of water