Energetics Flashcards
Enthalpy change
amount of heat energy taken in or given out during any change in a system
- provides pressure is contant and that standard conditions are 100kPA
Exothermic change
energy is transferred from the chemicals to the surroundings
- products have less energy than the reactants
H value in exothermic reaction
negative
endothermic reaction
energy transferred from the surroundings to the chemicals.
- they require an input of heat energy
- products have more energy than the reactants
H value in endothermic reaction
positive
standard enthalpy change of formation
enthalphy change when 1 mole of the compound is formed from its elements under standard conditions.
standard enthalpy change of combustions
enthalpy change that occurs when one mole of a substance is completely combusted in oxygen under standard conditions
enthalpy change of reaction
enthalpy change when the number of moles of reactants as specified in the balanced equation react together
enthaply change of neutralisation
enthalpy change when solutions of an acid and alkali react together under standard conditions, producing 1 mole of water
are enthalpy changes of neutralisations endo or exo
exothermic
enthalpy change of atomisation
enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state
hess’s law
the total enthalpy change for a reaction is independent of the route by which the chemical change takes place
hess law diagram when arrows point outwards
products - reactants
hess law diagrams when products point inwards
reactants - products
mean bond enthalpy
enthalpy needed to break the covalent bond into gaseuous atoms, averaged over different molecules
