1 - Energetics

Question 1

Average bond enthalpy

Answer 1

Energy required to break one mole of covalent bonds in the gas phase, averaged for that type of bond over many different compounds

Question 2

Enthalpy

Answer 2

Overall energy in a system

Question 3

Standard enthalpy change

Answer 3

Heat energy transferred in a reaction under standard conditions and constant pressure in kj/mol

Question 4

Standard Enthalpy Change of a Reaction (ΔrH°)

Answer 4

Enthalpy change of a reaction under standard conditions and constant pressure when one mole of a substance is reacted

Question 5

Standard Enthalpy Change of Formation (ΔfH°)

Answer 5

Enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions and constant pressure, with all reactants and products in their standard state

Question 6

Standard Enthalpy Change of Combustion (ΔcH°)

Answer 6

Enthalpy change when one mole of a substance reacts completely with oxygen under standard conditions and constant pressure, with all reactants and products in their standard state

Question 7

Why enthalpy change value can differ from data book

Answer 7

Heat loss

Incomplete combustion

Evaporation

Question 8

make experiment better (calorimetry)

Answer 8

1) Add lid
Reduces heat loss

2) Record temp for a suitable time
beforehand
Establishes accurate initial
temperature

3) Extrapolate cooling to point of
addition
Established theoretical max temp

Question 9

Hess’ Law

Answer 9

The enthalpy change in a reaction at constant pressure is independent of the route taken as long as the initial and final conditions are the same

Question 10

enthalpy change

Answer 10

The change in heat energy in a system at constant pressure