Kinetic theory definitions

Question 1

standard enthalpy change of reaction

Answer 1

the enthalpy change when a reaction takes place under standard conditions; refers to molar amounts of substances in the balanced chemical equation so balanced chemical equation must be given; may be exothermic or endothermic
Eg. 2Mg(s) + O2(g) to 2MgO(s) with DrH=-1204kJmol-1

Question 2

standard enthalpy change of formation

Answer 2

the enthalpy change when 1 mol of a compound is formed from its elements in their standard states under standard conditions; may be exothermic or endothermic
Eg. C(graphite) + 2H2(g) to CH4(g) DfH=-74.8

Question 3

standard enthalpy change of combustion

Answer 3

the enthalpy change when 1 mol of a compound burns completely in oxygen under standard conditions; always exothermic
Eg. C(graphite) + O2(g) to CO2(g) DcH=-393.5kJmol-1

Question 4

standard enthalpy change of hydration

Answer 4

the enthalpy change when 1 mol of gaseous ions dissolve in excess water to give 1 mol of aqueous ions (infinite dilution); always exothermic
Eg. Na+(g) to Na+(aq) DhydrH=-406kJmol-1

Question 5

standard enthalpy change of solution

Answer 5

the enthalpy change when 1 mol of an ionic substance dissolves in excess water (infinite dilution); may be exothermic or endothermic
Eg. NaCl(s) + excess water to NaCl(aq) DsolnH=+10kJmol-1

Question 6

standard enthalpy change of neutralisation

Answer 6

the enthalpy change when 1 mol of water (or salt) is made from an acid-base reaction under standard conditions; for strong acids and bases close to -57.9kJmol-1, less exothermic for weak acids/bases
Eg. NaOH(aq) + HCl(aq) to H2O(l) + NaCl(aq) DneutH=-57.9kJmol-1

Question 7

standard enthalpy change of vaporisation

Answer 7

the enthalpy change when 1 mol of liquid is converted into 1 mol of gas at its boiling point at standard pressure; always endothermic
Eg. H2O(l) to H2O(g) DvapH=+42kJmol-1

Question 8

first ionisation energy

Answer 8

the energy change when 1 mol of gaseous atoms loses 1 mol of electrons to form 1 mol of gaseous ions with a single positive charge; always endothermic
Eg. Na(g) to Na+(g) + e- Di1H=+494kJmol-1

Question 9

first electron affinity

Answer 9

the energy change when 1 mol gaseous atoms each gain an electron to form 1 mol of gaseous ions with a single negative charge; first electron affinity is exothermic, second and subsequent electron affinities are endothermic
Eg. Cl(g) + e- to Cl-(g) Dea1H=-380kJmol-1 (may also need to define second or subsequent electron affinities)

Question 10

lattice energy

Answer 10

the enthalpy change when 1 mol of an ionic compound is formed from its gaseous ions under standard conditions; always exothermic
Eg. Na+(g) + Cl-(g) to NaCl(s) DlattH=-775kJmol-1 (calculated from Born-Haber cycles)

Question 11

standard enthalpy of atomisation

Answer 11

the enthalpy change when 1 mol of gaseous atoms is made from the element in its standard state under standard conditions; always endothermic
Eg. C(graphite) to C(g) DatmH=+717kJmol-1

Question 12

bond enthalpy (bond energies)/mean bond dissociation energy

Answer 12

bond enthalpy (bond energy) represents the energy required to break 1 mol of a particular chemical bond in the gas phase (depends on precise environment of bond)

Question 13

standard conditions

Answer 13

100kPa pressure, solutions at 1moldm-3, at a stated temperature (normally 298K/25 degrees)

Question 14

enthalpy

Answer 14

the energy involved in the formation/breaking of chemical bonds in a particular reaction/a measure of the energy stored in something