Energetics

Question 1

Enthalpy Change

Answer 1

The heat energy change measured under conditions of constant pressure

Question 2

Mean bond enthalpy

Answer 2

Enthalpy required to break 1 mol of a covalent bond into gaseous atoms averaged over many molecules/compounds

Question 3

Standard enthalpy of formation

Answer 3

The enthalpy change when 1 mol of a substance is formed from its constituent elements in their standard states under standard conditions

Question 4

Standard enthalpy of combustion

Answer 4

The enthalpy change when 1 mol of a substance is completely burnt it excess oxygen with all other reactants being in their standard states under standard conditions

Question 5

Hess’s law

Answer 5

The enthalpy change for a reaction is independent of the route.
Given that the initial and final conditions remain the same

Question 6

Enthalpy Change equation

Answer 6

Break bonds + Make bonds
(+) (-)

Question 7

Specific heat capacity eq and definition

Answer 7

q= mcT
Energy required to raise 1g of substance by 1k without change of state
1cm3 of water = 1g of water

Question 8

Combustion Hess’s law

Answer 8

Arrows point towards central product
Always H2O and CO2

Question 9

Endo and Exo

Answer 9

Endo: + energy
~ temp decreases

Exo: - energy
~ temp increases