Energetics andd Thermochemistry
- Created by: BThorogood
- Created on: 02-03-15 08:14
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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
- When can we not measure enthalpy change directly?
- 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
- entropy change of the surroundings is the negative enthalpy of the system, over the absolute temperature
- 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
- ENTHALPIES OF HYDRATION
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