CHM136H1 Chapter Notes - Chapter 5: Bond-Dissociation Energy, Reagent, Methanol
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CHM136H1 Full Course Notes
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System + surroundings system- area of interest surroundings- everything else in the universe open system (most chemical reactions)- exchange energy + matter with surroundings closed system- exchange energy but not matter with surroundings. Most chemical reactions= exothermic e. g. combustion + neutralisation (transfer of heat from system > surroundings, products have less energy/ heat content than reactants) heat content= enthalpy. Combusion: ch4 (g) + 2o2 (g) > co2 (g) + 2h2o (l) h=-890kjmol-1. Endothermic- energy transfer from surroundings to system products have more heat content than reactants: h=+ photosynthesis: 6co2 + 6h2o (l) > 6c6h12o2 (aq) + 6o2 (g) h=+2802. 5kjmol- 1 standard enthalpy changes h temp: 298k pressure: 100kpa concentration: 1moldm-3 all substances in standard states. Enthalpy cycles enthalpy change for a particular reaction is calculated from the known enthalpy change of other reactions law of conservation of energy (energy change in complete cycle= 0)
