Energetics

Energetics

Definitions
1. Enthalpy Change
  1. The overall change in energy in a reaction. Measured in KJ/mol.
2. Hess' Law
  1. The energy change in a reaction is independent of the route taken.
3. Standard Enthalpy Change
  1. The amount of energy required with one mole of a substance in their standard states under standard conditions.
4. Standard Conditions
  1. 101kPa and 298K
5. Bond Enthalpies
  1. The energy required to break a bond. This varies depending on the atoms involved and the outside conditions.
Equations
1. q=mcΔT
2. Enthalpy change of a reaction = energy absorbed - energy released
Types of Reactions
1. Endothermic Reactions
  1. Takes in energy from the surroundings. Has +ve ΔH.
2. Exothermic Reactions
  1. Emits energy to the surroundings. Has -ve ΔH.
Calorimetry
1. You need to know the mass, temperature change and the number of moles of the reactants.
2. You can just measure the temperature change of reacting solutions.
3. For combustion, place the fuel in a calorimeter and measure the temperature change.
4. Problems
  1. Some heat is absorbed by the container.
  2. Some heat is lost to the surroundings (this always happens - even with insulation).
  3. With flammable liquids:
    1. Some combustion may be incomplete.
    2. Some flammable liquid may evaporate before burning.
General Information
1. Energy is required to break bonds and energy is released when bonds are formed.
2. Enthalpy changes include formation, combustion and reaction.
3. Formation enthalpies for all elements are zero.

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	Erstellt von Josh Bullock vor etwa 9 Jahre