[22.3] factors affecting lattice enthalpy & hydration

Question 1

what factors affect the values of lattice enthalpies?

Answer 1

• ionic size
• ionic charge

Question 2

what is the effect of large ionic size on lattice enthalpy? (eg. down a group)

Answer 2

• ionic radius increases
• attraction between ions decreases
• lattice energy becomes less negative
• melting point decreases

Question 3

what is the effect of increased ionic charge on lattice enthaly?

Answer 3

• ionic charge increases
• attraction between ions increases
• lattice energy becomes more negative
• melting point increases

Question 4

what factors affect hydration enthalpies?

Answer 4

• ionic size
• ionic charge

Question 5

what is the effect of increased ionic size on hydration enthalpy?

Answer 5

• ionic radius increases
• attraction between ion and water molecules decreases
• hydration enthalpy is less negative

Question 6

what is the effect of increased ionic charge on hydration enthalpy?

Answer 6

• ionic charge increases
• attraction with water molecules increases
• hydration energy becomes more negative

Question 7

what happens if a compound has a more negative lattice enthalpy?

Answer 7

• more exothermic (more energy released on formation)
• more energetically stable
• more likely to form

Question 8

how can you predict if an ionic compound will dissolve in water?

Answer 8

if the sum of the hydration enthalpies is larger than the magnitude of the lattice enthalpy, the overall enthalpy change (enthalpy change of solution) will be exothermic and the compound should dissolve