2.3.1 Enthalpy Changes 0.0 / 5 ? ChemistryEnthalpyASOCR Created by: upsidedown1004Created on: 01-06-16 13:37 What happen in an exothermic reaction? energy transferred from the system to the surroundings // products have less energy 1 of 11 What happens in an endothermic reaction? energy transferred from the surroundings ti the system // products have more energy // requires input of heat energy 2 of 11 What are the standard conditions of enthalpy changes? 100kPa / 289K / 1moldm^-3 concentration 3 of 11 What is the enthalpy change of reaction? enthalpy change when the number of moles of reactants as specified in the balanced equation react together 4 of 11 What is the standard enthalpy change of formation? enthalpy change when one mole of a compound is formed from its elements under standard conditions 5 of 11 What is standard enthalpy change of combustion? the enthalpy change that takes place when 1 mole of a substance reacts completely with oxygen under standard conditions 6 of 11 How do you calculate enthalpy change? Q = McT in joules 7 of 11 What is mean bond enthalpy? enthalpy change when 1 mole of bonds (gaseous covalent) are broken 8 of 11 How do you calculate bond enthalpy if all substances are gases? sum of bond energies broken - sum of bond energies made 9 of 11 Why are bond enthalpies calculated with gases less accurate? mean bond enthalpies are not exact 10 of 11 what is Hess's Law? total enthalpy change at a constant pressure for a reaction is independent of the route by which the chemical change takes place 11 of 11
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