Thermodynamics
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Define enthalpy of formation
The Enthalpy change/heat change at constant pressure when 1 mol of a substance is formed from its (constituent) elements with all reactants and products/all substances in standard states
Define enthalpy of combustion
The Enthalpy change/heat change at constant pressure when 1 mol of a substance is completely burned in oxygen with all reactants and products/all substances in standard states
Define enthalpy of lattice dissociation
Enthalpy change to separate 1 mole of an ionic substance into its gaseous ions
Define enthalpy of lattice formation
Enthalpy change to form 1 mole of an ionic substance from its gaseous ions
Define enthalpy of hydration
Enthalpy change when 1 mole of gaseous ions forms 1 mole of aqueous ions
Define enthalpy of solution
Enthalpy change when 1 mole of aqueous ions is formed from an ionic substance
what is meant by the ‘perfect ionic model’
• Perfect sphere • Only ionic bonding/elecrostatic attraction • No covalent character
Why is the electron affinity for fluroine negative?
Electrostatic FoA between nucleus and added electrons Energy is released when electrons are gained (exothermic)
What is the relationship between atomisation and mean bond enthalpy?
MBE = 2 x atomisation
Why is the enthalpy change calculated by the BH cycle greater than the theroetical value?
• Experimental value allows for covalent interaction/polarisation • Theoretical value assumes only ionic interaction
Why is the hydration of chloride exothermic?
• Water is polar/hydrogen is 𝛿+ • Cl- attracts H𝛿+
Why is entropy 0JK-1mol-1 at 0k?
Particles stationary because they have no energy Therefore no disorder