Unit 2: Ethanlpy Changes

Question 0

Describe the importance of oxidation

Answer 0

• exothermic reaction
• oxidation of fuels by combustion is our most exploited exothermic reaction
• we rely on combustion if petrol and diesel in cars and public transport.
• concern about how much fuel is burned and how much CO2 is produced.

Question 1

What do endothermic processes require?

Answer 1

An input of heat energy

Eg. Thermal decomposition of calcium carbonate

Question 2

Definition of standard conditions

Answer 2

A pressure of 100kPa
A temperature of 298K
A concentration of 1mol/dm^3

Question 3

Definition of enthalpy change of reaction

Answer 3

The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard styles.

Question 4

Definition of enthalpy change of formation

Answer 4

The enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.

Question 5

Definition of enthalpy change of combustion

Answer 5

The enthalpy change that takes place when:

• one mole of a substance reacts
• completely with oxygen
• under standard conditions, all reactants and products being in their standard states.

Question 6

Equation for energy change

Answer 6

Q=mc

Question 7

Definition of average bond enthalpy

Answer 7

The average enthalpy change that takes place when breaking by homolytic fission, 1 mol of a given type of bond in the molecules of a gaseous species.

Question 8

What is an exothermic reaction?

Answer 8

• Bond making, it releases energy.

- The bonds that are formed are stronger than the bonds that are broken

Question 9

What is an endothermic reaction?

Answer 9

• Bond breaking, it requires energy

- the bonds formed are weaker than the bonds that are broken.