Topic 13 Energetics II

Question 1

Why is the first electron affinity exothermic?

Answer 1

New force of attraction (FOA) between e- and nucleus made

Question 2

What is the first electron affinity equation

Answer 2

X (g) + e- -> X- (g)

Question 3

Why is second (and third and onwards) electron affinity endothermic?

Answer 3

Because adding e- and negative ions have repulsion
So energy needs to be put in to overcome

Question 4

What is the definition of electron affinity

Answer 4

Enthalpy change when one mole of electrons are added to one mole of atoms in the gaseous state to form one mole of anions

Question 5

What is the definition of standard enthalpy of atomisation

Answer 5

Enthalpy change when one mole of gaseous atoms are formed from the element in its constituent state under standard conditions

Question 6

What is the enthalpy of atomisation? + general equation

Answer 6

Exothermic
X (s) -> X(g)
One mole gas formed

Question 7

What is the lattice enthalpy of formation?

Answer 7

Enthalpy change When one mole of a solid compound is formed from its gaseous ions

Question 8

What is the standard enthalpy of formation?

Answer 8

Enthalpy change when one mole of a substance is formed from its constituent elements in standard conditions

Question 9

Why are theoretical and actual lattice energies different sometimes?

Answer 9

Bcs the theory assumes the ions are perfectly spherical but they may not be in reality

Question 10

What is the enthalpy of solution?

Answer 10

enthalpy change when 1 mole of substance is dissolved in water

Question 11

write the equation of enthalpy of solution of NaCl

Answer 11

NaCl (s) + aq -> Na+ (aq) + Cl- (aq)

Question 12

Suggest why calcium oxide is insoluble in water.

Answer 12

Because the lattice is so strong, lots of energy is needed to overcome

Question 13

Why is the second I.E. of calcium more exothermic than its first I.E.?

Answer 13

because e-s are pulled closer to the nucleus so more energy is needed to overcome

Question 14

how do sizes of ions affectlattice enthalpies?

Answer 14

• cations: the higher charge density/smaller = more perfectly spherical and ionic
• anions: the bigger/lower charge den, the more covalent
• evaluate impact to efoa and magnitude

Question 15

what are the cation anion combination for the perfect sphere shape lattice? (theoretically)

Answer 15

large, low charge den cation
small high charge den anion

Question 16

what are the cation anion combination for the perfect covalent lattice? (theoretically)

Answer 16

small, high charge den cation
large, low charge den anion