enthalpy change

Question 1

bond enthalpy

Answer 1

the energy needed to break 1 mole of bonds in a substance in their gaseous state.

Question 2

enthalpy change of formation

Answer 2

enthalpy change when 1 mole of a substance is formed from its elements under standard conditions.

Question 3

enthalpy change of combustion

Answer 3

enthalpy change when 1 mole of a substance is completely burnt in excess oxygen under standard conditions

Question 4

average bond enthalpy

Answer 4

(Average enthalpy change) when one mole of (gaseous covalent) bonds is broken

Question 5

enthalpy change of reaction

Answer 5

the enthalpy change when the number of moles of reactants as specified in the (balanced) equation react together

Question 6

whys the reaction exothermic

Answer 6

bond breaking absorbs energy bond making releases energy more energy is released than absorbed

Question 7

enthalpy change of neutralisation

Answer 7

Enthalpy change of neutralisation is the enthalpy change when 1 mole H2O is formed from the reaction of an acid/H+ with an alkali/base/OH–

Question 8

whys the reaction have a different value than expected

Answer 8

as bonds have different strengths in different environments