# Energetics andd Thermochemistry

HideShow resource information
• 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