Lattice enthalpy 166-167

Question 1

Define lattice enthalpy.

Answer 1

Lattice enthalpy is the enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.

Question 2

Define Hess’ law.

Answer 2

Hess’ law states that if a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route.

Question 3

Is lattice enthalpy always an exothermic or endothermic change?

Answer 3

Lattice enthalpy is an exothermic change. Lattice enthalpies have a negative sign because energy is given out when ionic bonds are being formed from gaseous ions.

Question 4

What is lattice enthalpy an indication of?(not definition)

Answer 4

Lattice enthalpy indicates the strength of an ionic lattice and is a measure of the ionic bond strength.

Question 5

Why can’t lattice enthalpies be measured directly?

Answer 5

For lattice enthalpy, one more of a solid ionic lattice is formed from its gaseous ions under standard conditions, but it is impossible to form one mole of an ionic lattice from gaseous ions.

Question 6

Define the standard enthalpy change of formation.

Answer 6

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

Question 7

Define the enthalpy change of atomisation.

Answer 7

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

Question 8

Define the first ionisation energy.

Answer 8

The enthalpy change accompanying the removal of one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Question 9

Define the second ionisation energy.

Answer 9

The enthalpy change accompanying the removal of one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.

Question 10

Define the first electron affinity.

Answer 10

The enthalpy change accompanying the addition of one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.

Question 11

Define the second electron affinity.

Answer 11

Second electron affinity is the enthalpy change accompaying the addition of one electron to each ion in one mole of gaseous 1- ions to form one mole of gaseous 2- ions.

Question 12

Is the standard change of formation endothermic or exothermic for an ionic compound?

Answer 12

This is usually an exothermic process for an ionic compound.

Question 13

Is the standard enthalpy change of atomisation an exothermic or endothermic process?

Answer 13

It is always an endothermic process because bonds have to be broken.

Question 14

Is the first ionisation and second ionisation energy an endothermic or exothermic process?

Answer 14

Both are endothermic processes because the electron(s) being lost have to overcome attraction from the nucleus in order to leave the atom.

Question 15

Is the first electron affinity an endothermic or exothermic process?

Answer 15

This is an exothermic process because the electron is attracted into the outer shell of an atom of a nucleus.

Question 16

Is the second electron affinity an endothermic or exothermic process?

Answer 16

This is an endothermic process because the electron is repelled by the 1- ion. This repulsion has to be overcome.