DF 1 

==Exothermic reaction== – a reaction that releases heat/energy to the surroundings. The temperature of the surroundings increases.

  • The products have less energy in their bonds than the reactants so the difference is released into the surroundings
    Endothermic reaction – a reaction that takes in heat/energy from the surroundings. The temperature of the surroundings decreases.
  • The products have more energy in the bonds than the reactants so the difference is taken in from the surroundings.
    in an endothermic energy level diagram, the reactants line should be lower than the products line.
    In an exothermic energy level diagram, the reactants line should be higher than the products line.

==Catalysts –== increase the rate of reaction by providing a different pathway of the reaction that has lower activation energy.

  • Catalysts change the rate of chemical reaction but are not used up in the reaction and therefore are not included in the chemical equation.
  • They are specific so different reactions require different catalysts
  • They allow a reaction to happen quickly but at a lower temperature which saves money.
    Enthalpy – the measure of the amount of heat energy in a system
    Enthalpy change = H products – H reactants
  • The enthalpy change tells you how much energy is transferred per mole of a substance
    Enthalpy change is worked out in standard conditions – 100kPa (1 atm) and 298k

==Standard enthalpy change for a reaction== = the enthalpy change when molar quantity’s of reactants, as stated in the equation, react together under standard conditions

==Standard enthalpy change of combustion== = the enthalpy change that occurs when one mole of a substance is burnt completely in oxygen under standard conditions

==Standard enthalpy change of formation== = the enthalpy change that occurs when one mole of a substance is formed from its elements under standard conditions

==Enthalpy change of neutralisation== = the enthalpy change when acid reacts with alkalis in aqueous solution under standard conditions. Defined per mole of H20