energetics

• what is enthalpy change?


  the heat energy change of a system measured under conditions of constant pressure
• what are the two types of reactions?


  • exothermic
  • endothermic
• what are examples of exothermic reactions?


  • combustion
  • neutrilisation
• what are examples of endothermic reactions?


  • thermal decomposition
  • photosynthesis
  • alkane cracking
• what happens to the energy in a exothermic reaction?


  it is released/given out
• what happens to the energy in a endothermic reaction?


  energy is absorbed/taken in
• what happens to the temperature in a endothermic reaction?


  decreases
• what happens to the temperature in a exothermic reaction?


  increases
• where may exothermic reactions be used?


  • chemical hand warmers
  • oxidations
  • fertilisers
• where may endothermic reactions be used?


  • disposable cool packs
  • dissolving salt in water
• what is activation energy?


  minimum amount of energy needed to break bonds and start a reaction
• whats standard enthalpy of combustion?


  enthalpy change when one mole of substance is completely combusted in excess oxygen. all substances are in standard state
• whats standard enthalpy of formation?


  enthalpy change when one mole of compound is formed from its constituent elements. all substances in their constant stat
• whats bond enthalpy?


  enthalpy change when one mole of covalent bond in the gas state is broken
• whats mean bond enthalpy?


  average enthalpy change when one mole of covalent bond in the gas state is broken. taken across a range of substances with that bond