Definitions

Question 1

State what is meant by the term COVALENT BOND

Answer 1

• (strong electrostatic) attraction

- between the two nuclei and the bonding pair of electrons

Question 2

What is a dative covalent bond?

Answer 2

• donation of a lone pair of electrons
• and the attraction between partial charges allow for a bond to be formed
• same property as a covalent bond

Question 3

What is Hess’s law

Answer 3

The enthalpy/energy change (for
a reaction) is independent of the
pathway taken

Question 4

Standard enthalpy change for Formation, ΔH°f

Answer 4

• Enthalpy change for when 1 mole of a substance is formed from its elements
• ALL reactants and products are in standard states (aq,g,l,s) and under standard conditions
  (100kPa, 298K)

Question 5

Standard enthalpy change for Combustion, ΔH°c

Answer 5

• Enthalpy change for when 1 mole of a substance is completely burned in oxygen
• ALL reactants and products are under standard conditions and in standard states (100kPa, 298K)

Question 6

The standard enthalpy change for Neutralisation, ΔH°n

Answer 6

-Enthalpy change when 1 mole of water (H2O) is formed when an acid and an alkali (base) react together under standard conditions and in standard states (100kPa, 298K)

Question 7

Standard enthalpy change of Reaction, ΔH°r

Answer 7

-The standard enthalpy change of a reaction is the enthalpy change which occurs when molar quantities of materials react under standard conditions, and with everything in its standard state (100kPa, 298K)

Question 8

What are the standard conditions?

Answer 8

• 100kPa (standard pressure)

- 298K (standard temperature)

Question 9

Exothermic

Answer 9

Heat energy is transferred to the surroundings

Question 10

Endothermic

Answer 10

Heat energy is transferred from the surroundings into the system

Question 11

Bond enthalpy

Answer 11

Enthalpy change when one mole of a bond in the gaseous state is broken

Question 12

Mean bond enthalpy

Answer 12

Enthalpy change when one mole of a bond, averaged over many different molecules, is broken