AS Chemistry - Enthalpy Changes

Sarah H-V
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Exothermic and Endothermic, Bond enthalpies, Calculating enthalpy changes

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Sarah H-V
Created by Sarah H-V over 4 years ago
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AS Chemistry - Enthalpy Changes
1 Exothermic and Endothermic
1.1 Endothermic
1.1.1 The absorption of energy to the surroundings
1.1.2 Delta H is positive
1.1.3 Themal Decomposition
1.1.4 Photosynthesis
1.2 Exothermic
1.2.1 The release of energy to the surroundings
1.2.2 Delta H is negative
1.2.3 Combustion
1.2.4 Respiration
2 Types of enthalpy change
2.1 Standard Enthalpy Change of Reaction
2.1.1 The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states
2.2 Standard Enthalpy Change of Combustion
2.2.1 The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard state
2.3 Standard Enthalpy Change of Formation
2.3.1 The enthalpy change that takes place when one mole of a compound is formed from its constituent elements under standard conditions, all reactants and products being in their standard states
3 Determining the enthalpy change
3.1 q= m x c x delta t
3.2 q - enthalpy change (Joules)
3.3 m - mass of surroundings involved in heat exchange
3.4 c - specific heat capacity
3.5 delta t - temperature change of surroundings
4 Bond Enthalpies
4.1 the enthalpy change that takes place when breaking by homolytic fission 1 mole of a given bond in the molecules of a gaseous species
4.2 Bond breaking - ENDOTHERMIC - energy is needed to break bonds
4.3 Bond making - EXOTHERMIC - energy is released when making bonds
4.4 Using average bond enthalpies to determine enthalpy changes
4.4.1 Delta H = the sum of the bond enthalpies of bonds broken -- the sum of the bond enthalpies of bonds made

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