5.2.1- Lattice Enthalpy Flashcards Preview

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Flashcards in 5.2.1- Lattice Enthalpy Deck (18):
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Define Lattice enthalpy (ΔHLE)

The enthalpy change that accompanies the formation of one mole of an
ionic compound from its gaseous ions (under standard conditions)

1

Is lattice enthalpy endo or exothermic

Lattice enthalpies are always negative (it is an exothermic process because bonds are made). The more negative (more exothermic), the stronger the ionic bonds.

2

Define the standard enthalpy change of formation

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

3

Define standard enthalpy change of atomisation

The enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state

4

Define first ionisation energy

The enthalpy change when one electron is removed from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

5

Define second ionisation energy

The enthalpy change when one electron is removed from each atom in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

6

Define the first electron affinity

The enthalpy change when one electron is gained by each atom in one mole of gaseous atoms (to form one mole of gaseous 1- ions)

7

Define second electron affinity

The enthalpy change when one electron is gained by each ion in one mole of gaseous 1- ions (to form one mole of gaseous 2- ions)

8

Why can't lattice enthalpies be determined experimentally

They cannot be measured directly because it is impossible to use gaseous ions to form one mole of an ionic lattice experiment

9

Is the enthalpy change of atomisation endothermic or exothermic?

Always endothermic because bonds have to be broken

10

Are ionisation energies endothermic or exothermic?

Always endothermic because the electron that has been lost has to overcome attraction from the nucleus in order to leave the atom

11

Is the first electron affinity endothermic or exothermic?

Exothermic because the electron is attracted into the outer shell of the atom by the nucleus

12

Is the second electron affinity endothermic or exothermic?

Endothermic because the electron is repelled by the 1- charge of the ion. This repulsion has to be overcome.

13

Defined the enthalpy change of solution

The enthalpy change that takes place when one mole of a compound is completely dissolved in water
Eg. KCl (s) + aq-> K+ (aq) + Cl- (aq)

14

What two processes take place when an ionic solid dissolves in water

1. Breakdown of ionic lattice into gaseous irons
2. Hydration of the ions

15

What is the breakdown of the ionic lattice equal to

The positive version of the lattice enthalpy

16

Define the enthalpy change of hydration

The enthalpy change for forming 1 mole of aqueous ions from 1 mole of gaseous ions

17

What is two factors affect lattice enthalpies?

LE are affected by (i) ionic radius: there is a greater attraction between smaller ions and so lattice enthalpies become more negative as ionic radius decreases (ii) ionic charge: there is a greater attraction between ions with higher charges and so lattice enthalpies become more negative as ionic charge increases.

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