energy changes

• What is the conservation of energy principle?

  Energy is conserved in chemical reactions. The amount of energy in the universe at the end of a chemical reaction is the same as before the reaction takes place.
• What is an exothermic reaction? Give examples

  A reaction where energy is transferred to the surroundings so that the surroundings temperature increases - combustion, oxidation reactions and neutralisation (acid + alkali) reactions. Negative sign of energy change.
• What is an endothermic reaction? Give examples

  A reaction where energy is taken in from the surroundings so the surroundings temperature decreases - thermal decomposition, reaction of citric acid and sodium hydrogencarbonate. Negative sign of energy change.
• What is activation energy.

  Minimum amount of energy that particles need to react
• What is a reaction profile?

  Reaction profile is a graph which shows the relative energies of reactants and product, as well as activation energy of the reaction.
• What occurs in a chemical reaction in terms of bond energies?

  Energy is supplied to break bonds and energy is released when bonds are made
• Describe rechargeable and non-rechargeable cells

  Rechargeable - chemical reactions are reversed when an external current is supplied

  Non-rechargeable - reactants are used up, cannot be recharged
• What is the principle of energy conservation in chemical reactions?

  The total amount of energy in the universe remains the same before and after a reaction.
• What happens to energy during an exothermic reaction?

  Energy is transferred to the surroundings, causing the temperature of the surroundings to increase.
• What are some examples of exothermic reactions?

  Combustion reactions, many oxidation reactions, and most neutralisation reactions.
• What are everyday uses of exothermic reactions?

  Self-heating cans and hand warmers.
• What occurs during an endothermic reaction?

  Energy is taken in from the surroundings, causing the temperature of the surroundings to decrease.
• What are some examples of endothermic reactions?

  Thermal decomposition reactions and the reaction of citric acid with sodium hydrogencarbonate.
• What is a common everyday use of endothermic reactions?

  Instant ice packs used to treat sports injuries.
• What does an energy level diagram show in a chemical reaction?

  • Energy in the reactants and products
  • Difference in energy between reactants and products
  • Indicates whether the reaction is exothermic or endothermic
• How does the energy level change in an exothermic reaction?

  The energy level decreases because energy is given out to the surroundings.
• How does the energy level change in an endothermic reaction?

  The energy level increases because energy is taken in from the surroundings.
• What is a reaction profile and what does it include?

  • Shows how energy changes during a reaction
  • Includes activation energy
  • Indicates the energy of reactants and products
• What is activation energy?

  It is the minimum energy needed by particles when they collide for a reaction to occur.
• How is activation energy represented in a reaction profile?

  As a 'hump' in the line that starts at the energy of the reactants.
• What determines whether a reaction is exothermic or endothermic?

  The difference between the energy needed to break bonds and the energy released when new bonds are made.
• When is a reaction considered exothermic?

  When more heat energy is released in making bonds in the products than is taken in when breaking bonds in the reactants.
• When is a reaction considered endothermic?

  When less heat energy is released in making bonds in the products than is taken in when breaking bonds in the reactants.
• What do chemical cells use to transfer energy?

  Chemical reactions
• What factors affect the voltage of a chemical cell?

  The materials of the electrodes and the substance used as the electrolyte
• How can a simple cell be made?

  By connecting two different metals in contact with an electrolyte
• What happens when multiple cells are connected in series?

  The voltage increases compared to a single cell
• What occurs in non-rechargeable cells when one of the reactants is used up?

  The battery 'goes flat'
• How do rechargeable cells and batteries work?

  The chemical reactions can be reversed when an external circuit is supplied
• What do fuel cells require to produce voltage continuously?

  A constant supply of a suitable fuel and oxygen
• How is the fuel oxidised in fuel cells?

  Electrochemically, rather than being burned
• What type of energy is released by fuel cells?

  Electrical energy
• What are the pros and cons of alkaline cells, rechargeable cells, and hydrogen fuel cells?

  Alkaline Cell:

  • Pros: Cheaper to manufacture
  • Cons: May end up in landfill sites once fully discharged

  
  

  Rechargeable Cell:

  • Pros: Can be recharged many times, reducing resource use
  • Cons: Costs more to manufacture

  
  

  Hydrogen Fuel Cell:

  • Pros: Small size; water is the only chemical product
  • Cons: Very expensive to manufacture; needs a constant supply of hydrogen fuel
• In what applications are fuel cells commonly used?

  In spacecraft and vehicles
• What is the process of electrolysis?

  Decomposition of ionic compounds using electricity.
• What is an electrolyte?

  A liquid that conducts electricity.
• What does it mean to discharge in the context of electrolysis?

  To gain or lose electrons to become electrically neutral.
• What is the role of the anode in electrolysis?

  It is the electrode where oxidation takes place and is the positive electrode.
• What occurs at the cathode during electrolysis?

  Reduction takes place, which is the gain of electrons, and it is the negative electrode.
• What are the key terms related to electrolysis and their definitions?


  • Electrolysis: Decomposition of ionic compounds using electricity.
  • Electrolyte: A liquid that conducts electricity.
  • Discharge: Gain or lose electrons to become electrically neutral.
  • Anode: Electrode where oxidation takes place (positive electrode).
  • Cathode: Electrode where reduction takes place (negative electrode).