Energetics

Energetics

Endothermic and Exothermic Reactions
1. Thermochemistry
  1. The study of heat changes during chemical reactions
  2. Energy taken in when bonds are broken
    1. Energy is released when bonds are made
      1. Exothermic
      2. If a reaction is endothermic is one direction, it is always exothermic in the other directions (vice versa)
    2. Endothermic
  3. Energy is measured in KJ/Mol
  4. When fuels are burnt, there is an exothermic reaction
Enthalpy
1. Enthalpy Change, (Delta)H
  1. A heat change at constant pressure
2. The physical states of the products and reactants affect the enthalpy change
3. -ve = Exothermic
  1. +ve = Endothermic
Measuring enthalpy changes
1. Standard molar enthalpy of formation
  1. "The enthalpy change when one mole of compound is formed from its constituent elements under standard conditions, all reactants and products in their standard states"
  2. ARROWS POINT TO THE RIGHT
2. Standard molar enthalpy of combustion
  1. "The enthalpy change when one mole of compound is completely burned in oxygen under standard conditions, all reactants and products in their standard states"
  2. ARROWS POINT DOWN
3. q = m x c x (Delta)T
  1. q = J
    1. m = mass
      1. c = Specific heat capacity
        (Delta) T = temperature change
4. Calorimeter used to measure enthalpy change
  1. Mass of product heated
  2. Temperature change
Hess' Law
1. The enthalpy change for a chemical reaction is the same, whatever route is taken from reactants to products
2. Thermochemical Cycles
  1. LOOK IN BOOK
Bond Enthalpies
1. The mean bond enthalpy
  1. Same bond may have different bond enthalpies under different environments

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