Thermochemistry

• define thermochemistry

  study of heat changes in chemical reactions
• exothermic reactions


  produce heat

  temperature rises

  (ΔH) is negative

  involves making bonds
• endothermic reactions


  absorbs heat

  temperature falls

  (ΔH) is positive

  involves breaking bonds
• sublimation


  straight from a solid to a gas without becoming a liquid
• heterogeneous catalysis


  catalyst and reactant are in different phases
• homogenous catalyst


  catalyst and reactant are in the same phases
• bond energy


  average energy required to break one mole of bonds into neutral gaseous atoms
• heat of combustion


  heat change when one mole of a substance is completely burned in excess oxygen
• heat of reaction


  heat change when the number of moles in the balanced equation react
• heat of formation


  heat change when one mole of a compound is formed from its elements in their standard states
• Hess's law


  the heat change for a reaction is the same whether the reaction takes place in one step or several steps
• Law of Lavoisier and Laplace

  heat change for the forward reaction is equal to the heat change for the reverse reaction, but opposite in sign
• heat of combustion is measured using a bomb calorimeter
• bomb calorimeter formula


  H=mcΔT

  m=mass

  c=specific heat capacity

  ΔT= change in temperature
• bomb calorimeter is used to measure heat of combustion accurately & find the calorific value of food
• kilogram calorific value - the heat produced when 1kg of a fuel is completely burned in excess oxygen
• bomb calorimeter is

  fast

  complete

  no heat is lost