Energetics

Question 1

Enthalpy definition

Answer 1

Measure of heat content of a substance

Question 2

Enthalpy change definition

Answer 2

Change in heat content at constant pressure

Question 3

Standard conditions

Answer 3

100kPa and a stated temperature (298k)

Question 4

Enthalpy of reaction

Answer 4

Reactants in stoichiometric equation react to give products under standard conditions
Endo/exo

Question 5

Enthalpy of formation

Answer 5

One mole of a compound formed from its individual elements under standard conditions
Endo/exo

Question 6

Enthalpy of combustion

Answer 6

One mole of a substance burnt in excess oxygen under standard conditions
Exo

Question 7

Enthalpy of neutralisation

Answer 7

One mole of water formed by reacting acid and alkali under standard conditions
Exo

Question 8

Exothermic enthalpy

Answer 8

Heat energy given out to surroundings
- delta H
Reactant enthalpy > products
Reactant stability < product

Question 9

Endothermic enthalpy

Answer 9

Heat energy absorbed from surroundings
+ delta H
Reactant enthalpy < products
Reactant stability > product

Question 10

Why are conditions important

Answer 10

Cant directly measure enthalpy
Experimental data effected by temperature and pressure
Must be constant to validity results

Question 11

Hess’s law

Answer 11

Total enthalpy change of a reaction is always the same irrelevant of the route taken

Question 12

Bond enthalpy

Answer 12

Energy needed to break one mole of a type of covalent bond in a gaseous state molecule

Question 13

Mean bond enthalpy

Answer 13

Energy needed to break one mole of bonds of many gaseous compounds

Question 14

Bond strength

Answer 14

Not constant
Higher ESA, higher energy to break, higher strength