Energetics Chem2

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  • Created by: menka
  • Created on: 10-05-13 09:38

Definitions

Enthalpy Change A measure of heat energy given out or taken in when a chemical or physical change occurs at constant pressure.

Standard molar enthalpy change of combustion The amount of heat energy given out when 1 mole of a substance is compeltely burned in oxygen with all reactants and products in their standard states and conditions.

Standard molar enthalpy change of formation The change when 1 mole of substance is formed from its elements with all reactants and products in their standard states and conditions.

Standard states 100kPa and 289K (25C)

Mean bond enthalpy The energy that must be put in to break a particular bond. It is the average for the bond in question taken over a range of compounds containing that bond.

Exothermic Gives out energy to surroundings, so temperature drops. (enthalpy=negative)

Endothermic Takes in energy from surroundings, so temperature rises. (enthalpy=positive)

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Useful Equations

Mean bond enthalpy = ∑bonds broken - ∑bonds formed

Standard molar enthalpy change of combustion = ∑Reactants - ∑Products

Standard molar enthalpy change of formation = ∑Products - ∑Reactants

q=mcΔT

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Hess' Law

Definition The total emthalpy change of a reaction is always the same no matter what route is taken.

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