17.3- MORE ENTHALPY CHANGES

Question 1

What can ionic compounds only dissolve well in?

Answer 1

polar solvents

Question 2

What must happen to dissolve an ionic compound?

Answer 2

lattice must be broken up

Question 3

What is required for a lattice to be broken?

Answer 3

input of energy- lattice enthalpy

Question 4

What happens when the ions of a lattice are separated and solvated?

Answer 4

separate ions solvated by solvent molecules, usually water
these cluster round ions so positive ions surrounded by negative ends of dipole of water molecules + negative ions surrounded by positive ends of dipoles of water molecules

Question 5

What is it called when separate ions are solvated and the solvent is water?

Answer 5

hydration

Question 6

What trend does the enthalpy change of hydration show?

Answer 6

more negative for more highly charged ions and less negative for bigger ions

Question 7

What three processes sum up the process of dissolving an ionic compound?

Answer 7

1. breaking ionic lattice to give separate gaseous ions- lattice dissociation enthalpy has to be put in
2. hydrating positive ions (cations)- enthalpy of hydration given out
3. hydrating negative ions (anions)- enthalpy of hydration given out

Question 8

For ionic compounds, what is the enthalpy change of solution like?

Answer 8

rather small value value + may be positive or negative

Question 9

What is needed to work out the theoretical value for the lattice formation enthalpy of an ionic compound?

Answer 9

charge on ions, their distance apart, geometry of its structure

Question 10

What are factors that increase polarisation? (2)

Answer 10

positive ion (cation)- small size, high charge

negative ion (anion) - large size, high charge