Module 3✌️

Question 1

Why do bond enthalpies have positive values?

Answer 1

Bond breaking is endothermic

Question 2

Standard enthalpy change of combustion?

Answer 2

The enthalpy change that takes place when 1 mole of a substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard states.

Question 3

Exothermic?

Answer 3

• a reaction that releases heat

- has a negative ^H

Question 4

Why standard enthalpy change of combustion will be different from the ones calculated by average bond enthalpies?

Answer 4

• actual bond enthalpies may be different from average values
• non standard conditions

Question 5

Standard enthalpy change of formation?

Answer 5

The enthalpy change that takes place when 1 mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states, 25c and 101 kPa

Question 6

Reasons for difference between calculated value and one obtained experimentally?

Answer 6

Incomplete combustion

Non standard conditions