module 5: physical chemistry and transition elements

Question 1

what is lattice enthalpy?

Answer 1

the enthalpy change when one mole of an ionic compound is formed from its gaseous ions, under standard conditions

Question 2

is the value for lattice enthalpy change always positive or negative, and why?

Answer 2

negative, lattice enthalpy involves ionic bond formation from separate gaseous ions which is an exothermic change

Question 3

what are the key features about lattice enthalpy?

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
• lattice enthalpy is a measure of the strength of ionic bonding in a giant ionic lattice, a large negative value shows that there are strong electrostatic forces of attraction between the oppositely charged ions in the lattice
• a covalent substance does not have a lattice enthalpy because there are no ions in its structure
• lattice enthalpies cannot be measure directly because it is impossible to form a mole of an ionic lattice from gaseous ions

Question 4

how are lattice enthalpies calculated indirectly?

Answer 4

Born-Haber cycle

Question 5

what is the standard enthalpy change of atomisation?

Answer 5

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

Question 6

why is the standard enthalpy change of atomisation always an endothermic process?

Answer 6

energy is taken in for bond breaking to form gaseous atoms

Question 7

what is electron affinity?

Answer 7

measures the energy to gain electrons

Question 8

what is the difference between electron affinity and ionisation energy?

Answer 8

electron affinity is the opposite of ionisation energy
- electron affinity measures the energy to gain electrons
- ionisation energy measures the energy to lose electrons

Question 9

what is the first electron affinity?

Answer 9

the enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

Question 10

why can lattice enthalpies not be determined directly?

Answer 10

you cannot form one mole of an ionic lattice from gaseous ions

Question 11

what are the equations for making the solid sodium chloride?

Answer 11

• atomisation of sodium
• atomisation of chlorine
• ionisation of sodium
• electron affinity of chlorine