Energetics I Flashcards
State ‘standard’ pressure and temperature conditions
100 kPa
298 K
Define ‘Enthalpy Change’
The amount of heat absorbed or released in a chemical reaction occurs at constant pressure
Which enthalpy change values are positive/negative?
Exothermic - negative
Endothermic - positive
Define the ‘Standard enthalpy of reaction’
Enthalpy change for a reaction that takes place under standard conditions, molar quantities as given in an equation.
Define the ‘Standard enthalpy of formation’
Enthalpy change for the formation when 1 mole of substance, from elements in its standard states, under standard conditions.
Define the ‘Standard enthalpy of combustion’
Enthalpy change when 1 mole of substance is [complete] combusted in excess oxygen under standard conditions
Define the ‘Standard enthalpy of neutralisation’
Enthalpy change when an acid and a base react to form 1 mole of water under standard conditions.
What formula is used to calculate enthalpy change in KJ/mol
Q = mass of water x specific heat capacity of water x temperature change
ΔH = Q/number of moles x10-3
Define ‘Bond enthalpy’
The energy required to break 1 mole of a particular bond in the gaseous state.
Define ‘Average Bond Enthalpy’
The average energy required to break 1 mole of a bond in the gaseous state
What are the limitations of calculating enthalpy change from mean bond enthalpies?
- Average bond enthalpy will differ from the specific bond enthalpy
- mean value is not calculated from all compounds containing C-H
What’s the GCSE formula for bond enthalpy
The sum of Bonds broken - The sum of Bonds made
