Topic 8: Chemical energetics

Question 1

exothermic:

Answer 1

heat energy is transferred from the system to the surroundings

Question 2

endothermic:

Answer 2

heat energy is transferred from the surroundings tot he system

Question 3

standard enthalpy change of reaction(ΔrH°) is

Answer 3

the enthalpy change measured at 100kPa and a stated temperature, usually 298 K, when the number of moles of substances in the equation as written react

Question 4

standard enthalpy change of combustion (ΔcH°) is

Answer 4

the enthalpy change measured at 100kPa and a stated temperature, usually 298 K, when one mole of a substance is completely burned in oxygen

Question 5

standard enthalpy change of neutralisation (ΔneutH°) is

Answer 5

the enthalpy change measured at 100kPa and a stated temperature, usually 298 K, when one mole of water is produced by the neutralisation of an acid with an alkali

Question 6

standard enthalpy change of formation (ΔfH°) is

Answer 6

the enthalpy change measured at 100kPa and a stated temperature, usually 298 K, when one mole of a substance is formed from its elements in their standard states

Question 7

Hess’s Law states that

Answer 7

the enthalpy change of a reaction is independent of the path taken in converting reactants into products, provided the initial and final conditions are the same in each case

Question 8

bond enthalpy is

Answer 8

the enthalpy change when one mole of a bond in the gaseous state is broken

Question 9

mean bond enthalpy is

Answer 9

the enthalpy change when one mole of a bond, averaged out over many different molecules, is broken