Defintions

Question 1

Standard enthalpy of combustion

Answer 1

The enthalpy change when one mole of a substance in its standard state burns completely in oxygen under standard conditions of 298K and 1 bar pressure.

Question 2

Enthalpy of formation

Answer 2

The enthalpy change when one mole of a substance is formed in its standard state from the pure elements in their standard states under standard conditions of 298K and 1 bar pressure.

Question 3

Bond enthalpy

Answer 3

enthalpy change when one mole of bonds is broken in the gas phase

Question 4

Mean bond enthalpy inaccuracies

Answer 4

-Mean bond enthalpies are only valid in the gas phase. You might not be doing your reaction in the gas phase.

-Bond enthalpies depend on the particular molecule, whereas mean bond enthalpies are quoted generally (

Question 5

Mean bond enthalpy

Answer 5

Average bond enthalpies taken from different molecules with the same bond

it is a mean because exact bond enthalpies change depending on molecule

E.g the exact bond enthalpy of the C-C bond in ethane and ethanol (different environments ) won’t be the same but we can get an average of both to get a mean bond enthalpy for the C-C bond