enthalpies, born haber, entropy + free energy

week 3, question 2

hess’ law definition

total enthalpy change accompanying a chemical change is independent of the route by which the change takes place

change in enthalpy of reactants

sum of product enthalpy - sum of reactant enthalpy

standard enthalpy of combustion

• one mole of a substance undergoes complete combustion

• under standard conditions

calculation of ΔHc^θ from experimental data

1. q = mcΔT

2. mols of fuel burned = mass loss/ RFM

3. energy released per mol of fuel = -(q/1000 / mols)

assumptions of ΔHc^θ

• all energy released is transferred to the water in calorimeter

• combustion is complete and forms CO2 and H2O only

errors of ΔHc^θ

• heat lost to air = reduced

• incomplete combustion = less exo

lattice dissociation energy

• 1 mol of lattice is broken up

• into isolated gaseous ions

• at 1 atmosphere pressure and 298K

enthalpy of formation

• 1 mol of a compound if formed

• from its constituent elements

• in standard states

enthalpy of atomisation of an element

• 1 mol of gaseous atoms is made

• from the element

• in standard states under standard conditions

ionisation energy is the energy required to

• remove 1 electron from each atom

• in 1 mol of gaseous atoms

• to form 1 mol of gaseous unipositive ions

first electron affinity is the enthalpy change accompanying

• the gain of 1 mol of electrons

• by 1 mol of atoms

• in the gaseous phase

increase in temperature (q = mcat)

exothermic

decrease in temperature (q = mcat)

endothermic