Edexcel A Level Chemistry: Energetics

what is an exothermic reaction?

reaction energy transferred to surroundings, system loses energy, ΔH negative

what is an endothermic reaction?

reaction energy transferred from surroundings, system gains energy, ΔH positive

what are standard conditions?

298K, 100kPa

what is the standard enthalpy change of a reaction?

enthalpy change when reactants are in their standard states under standard conditions, and with everything in its standard state.

what is the Standard enthalpy change of formation, ΔH°f?

enthalpy change when one mole of compound formed from its elements in their standard states under standard conditions

what is the Standard enthalpy change of combustion, ΔH°c ?

enthalpy change when one mole of compound is burned completely in oxygen under standard conditions

what is lattice dissociation enthalpy?

enthalpy change needed to convert 1 mole of solid crystal to its gaseous ions (positive)

what is lattice formation enthalpy?

enthalpy change when 1 mole of solid crystal is formed from its gaseous ions (negative)

what two main factors affect lattice enthalpy?

charges on the ions, ionic radii

what is standard atomisation enthalpy, ΔH°a. ?

enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state (positive)

why are theoretical and experimental values for lattice enthalpy different?

theoretical values assume 100% ionic

what is Hess' Law?

enthalpy change accompanying a chemical change is independent of the route by which the chemical change occurs

what is enthalpy change of solution?

enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution.

what is enthalpy change of hydration?

enthalpy change when 1 mole of gaseous ions dissolve in sufficient water to give an infinitely dilute solution (negative)

give two factors that affect hydration enthalpy

size and charge of the molecule

what is Enthalpy change of neutralisation?

enthalpy change when solutions of an acid and an alkali react together under standard conditions to produce 1 mole of water

give the equation to calculate energy transferred (Q)

energy transferred in J (Q) = mass of solution (m) x 4.18 (c) x change in temp (ΔT)

give the equation to calculate ΔH from energy transferred

ΔH = energy transferred in kj / number of moles

what is first electron affinity?

energy change when each atom in one mole of gaseous atoms gains an electron to form one mole of gaseous ions with single negative charge