topic 3: chemical energy

Question 1

define enthalpy

Answer 1

a measure of the chemical energy in a substance

Question 2

what is the enthalpy of combustion

Answer 2

the enthalpy of combustion is when one mole of a substance is burned completely in oxygen

Question 3

give 2 reasons why the enthalpy of combustion of ethanol by experiment is lower than the data book value

Answer 3

•heat loss to environment
•incomplete combustion of fuel

Question 4

define enthalpy of solution

Answer 4

when one mole of a substance is disolved completely in water

Question 5

define enthalpy of neutralisation

Answer 5

when an acid is neutralised to form 1 mole of water

Question 6

what is the meaning of hess’s law

Answer 6

the enthalpy change of a given reaction is the same no matter which route is taken to get there

Question 7

define molar bond enthalpy

Answer 7

the energy required to break one mole of bonds in a diatomic molecule

Question 8

what is mean bond enthalapy

Answer 8

the average energy required to break one mole of bonds, for a bond that occurs in a number of molecules