Energetics andd Thermochemistry

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  • ENERGETICS AND THERMO-CHEMISTRY
    • ENTHALPIES OF HYDRATION
      • When can we not measure enthalpy change directly?
        • when there's no change
        • when there's little change
        • when there's lots of change
      • Percentage uncertainty= (uncertainty/measured value) x100
      • extrapolate exothermic reactions to get the max. temperature
      • Born-Haber cycle
    • ENTROPY
      • The more disordered a system, the higher the entropy.
      • Measured in Joules per Kelvin per mole
      • change in S = finalS - initialS
      • The universe is constantly moving towards its most disordered state.
      • Factors Affecting Entropy
        • The state: Solids have a lower entropy because they have ways to organise their particles.
        • The number of particles: The more particles there are, the more ways the particles can be arranged, so the higher the entropy.
        • The size of the molecule: The smaller the molecule, the lower the entropy, because there are more ways to arrange the particles.
    • Spontaneity
      • entropy change of the surroundings is directly proportional to the negative change of enthalpy of the system
      • entropy change of the surroundings is inversely proportional to the absolute temperature
        • entropy change of the surroundings is the negative enthalpy of the system, over the absolute temperature
          • entropy change of the surroundings is directly proportional to the negative change of enthalpy of the system
    • GIBBS FREE ENERGY
      • The change in the Gibbs Free Energy of a reaction can be used as a measure of the spontaneity of a reaction.
      • If Gibbs Free Energy is negative, the reaction is spontaneous.
      • At 298K: change in G of the reaction = sum of the change in G of the formation of the products - the change in G of the formation of the reactants
      • At any temperature: change in G = change in enthalpy - absolute temperature x change of entropy

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