Energetics

Question 1

Enthalpy change definition

Answer 1

heat energy exchange
under constant pressure

Question 2

Standard Enthalpy Change of Combustion

Answer 2

• when 1 mole of substance
• is burned in excess oxygen / completely burned in oxygen
• under standard conditions in standard states

Question 3

Standard Enthalpy Change of Formation

Answer 3

• when 1 mole of substance is formed
• form its elements
• under standard conditions in standard states

Question 4

Hess’ Law

Answer 4

• if a reaction can take another route
• with start and end conditions being the same
• enthalpy change is the same

Question 5

Situations where a Hess Cycle would be used (3)

Answer 5

1. slow rate of reaction
2. multiple reactions occuring
3. high activation energy

Question 6

Standard conditions + values

Answer 6

1. temperature of 298K
2. pressure of 1 atm, 101kPa
3. standard states
4. concentration of 1.0 mol/dm3

Question 7

Hess’s Law (textbook)

Answer 7

enthalpy change in a reaction

is independent of the route

and depends only on initial and final states

Question 8

mean bond enthalpy meaning

Answer 8

average enthalpy required to break a covalent bond across different molecules