electrochemistry

• Energy

  Absorbed to break bonds and released to form bonds
• Enthalpy change

  The net value of energy absorbed from and released to the surroundings
• Exothermic reaction

  A chemical reaction in which heat energy is released to the surroundings
• Exothermic reactions

  • Neutralization
  • Combustion
  • Respiration
• Exothermic processes

  • Freezing
  • Condensation
  • Dissolution of acid and alkalis in water
  • Dissolving anhydrous salts
• Reactants in an exothermic reaction lose energy
• In an exothermic reaction, the final temperature is higher than the initial temperature
• In exothermic reaction, formation of bond is present and the enthalpy change is negative
• The overall reaction is exothermic when more energy is released during bond forming than needed for bond breaking
• In an exothermic reaction, the products contain less energy than reactants hence exothermic changes have negative enthalpy change
• Endothermic reaction

  A chemical reaction in which heat energy is absorbed from the surroundings
• Endothermic reactions


  • Thermal decomposition
  • Photosynthesis
• Endothermic processes

  • Boiling
  • Melting
  • Sublimation
  • Dissolution of some ionic compounds in water such as ammonium chloride, sodium chloride and barium nitrate
• Reactants in an endothermic reaction gain energy
• In an endothermic reaction, final temperature is lower than initial temperature
• In an endothermic reaction, breaking of bond is present and enthalpy change is positive
• The overall reaction is endothermic when more energy is absorbed for bond breaking than needed for bond forming
• In endothermic reaction, products contain more energy than reactants hence endothermic changes have positive enthalpy change
• Activation energy

  The minimum amount of energy that colliding reactant particles must possess to react with one another
• Energy profile diagram

  A diagrammatic representation to show energy change where the x axis is labelled energy and the y axis is labelled progress of reaction
• Energy level diagram

  A diagrammatic representation to show energy change where the x axis is labelled energy level and there is no y axis
• Energy level diagram

  1. Put in state symbols

  2. Label reactants and products with position dependent on whether exothermic or endothermic

  3. Write enthalpy change value and draw arrow from reactant to product

  4. Draw activation energy arrow from reactant to peak
• Energy profile diagram

  1. Put in state symbols

  2. Label reactants and products with position dependent on whether exothermic or endothermic

  3. Write enthalpy change value and draw arrow from reactant to product

  4. Draw activation energy arrow from reactant to peak