Definitions Flashcards
State what is meant by the term COVALENT BOND
- (strong electrostatic) attraction
- between the two nuclei and the bonding pair of electrons
What is a dative covalent bond?
- 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
What is Hess’s law
The enthalpy/energy change (for
a reaction) is independent of the
pathway taken
Standard enthalpy change for Formation, ΔH°f
- 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)
Standard enthalpy change for Combustion, ΔH°c
- 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)
The standard enthalpy change for Neutralisation, ΔH°n
-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)
Standard enthalpy change of Reaction, ΔH°r
-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)
What are the standard conditions?
- 100kPa (standard pressure)
- 298K (standard temperature)
Exothermic
Heat energy is transferred to the surroundings
Endothermic
Heat energy is transferred from the surroundings into the system
Bond enthalpy
Enthalpy change when one mole of a bond in the gaseous state is broken
Mean bond enthalpy
Enthalpy change when one mole of a bond, averaged over many different molecules, is broken
