Enthalpy Change Of Solution

Question 1

The enthalpy change of solution

Answer 1

The enthalpy change when 1 mole of an ionic compound in its standard state dissolved in water and form an ionic solution such that their ions are far enough apart to not interact under standard conditions

Question 2

What must happen in ionic bonds within an ionic solute for it do dissolve in water?

Answer 2

Must break which is an endothermic process, breaking bonds requires energy put in

Question 3

What must happen in bonds within the water and ionic solute for it to dissolve?

Answer 3

New bonds must be formed called ion-dipole forces which is an exothermic process (making bonds releases energy)

Question 4

Ion-dipole forces formed must be….

Answer 4

The same strength or of greater strength than the bonds broken in the ionic compound/lattice
Aka releases more energy making the ion-dipole forces than breaking ionic compounds in lattice

Question 5

The process of dissolving is usually… and why?

Answer 5

Exothermic because more energy is released making ion-dipole forces between ions than taken in when breaking bonds in the ionic compound
So overall there is a release in energy

Question 6

What process of dissolving is endothermic?

Answer 6

Breaking ionic bonds in the ionic lattice as it releases energy

Question 7

What process of dissolving is exothermic?

Answer 7

Hydration, the formation of ion- dipole bonds releases energy

Question 8

Ion-dipole forces

Answer 8

The forces between H d+ on water and the negative ion
The forces between O d- on water and the positive ion
Once the ions are hydrated when dissolved in solution

Question 9

What 2 pieces of information do we need to know when calculating the enthalpy changes of solution?

Answer 9

The lattice dissociation enthalpy
The enthalpies of hydration for each ion

Question 10

Lattice dissociation enthalpy

Answer 10

The enthalpy change when 1 mole of a compound is split into its constituent gaseous ions

Question 11

Enthalpy of hydration of an ion

Answer 11

The enthalpy change when 1 mole of gaseous ions dissolved in water to form 1 mole of aqueous ions

Question 12

How can we find the enthalpy of solution?

Answer 12

Using a born haber cycle
Or using an equation

Question 13

Born haber cycle to work out enthalpy of solution has what values at the top?

Answer 13

Gaseous ions

Question 14

What goes below the gaseous ions in the born haber cycle?

Answer 14

Enthalpies of hydration (aqueous ions)
Lattice enthalpy of formation with arrow pointing down OR Lattice enthalpy of dissociation with arrow pointing up (The ionic solid)

Question 15

The enthalpy of solution in the born haber cycle is…

Answer 15

The arrow from the ionic solid pointing to the aqueous ions in the middle

Question 16

How to find Enthalpy of solution as an equation

Answer 16

= -(lattice enthalpy of formation) + (sum of hydration enthalpies)
Or
=(lattice enthalpy of dissociation) + (sum of hydration enthalpies)

Question 17

Which route do we use to work out the enthalpy of solution in the born haber cycle?

Answer 17

From the ionic solid to the aqueous ions
This is either direct arrow, or via the enthalpy change of formation/dissociation + hydration enthalpies

Question 18

If we go against the arrow in a born haber cycle…

Answer 18

The value’s sign will flip!

Question 19

What can effect enthalpies of hydration

Answer 19

The charge of the ion
The size of the ion

Question 20

How does charge of an ion affect the enthalpy of hydration?

Answer 20

Ion with a high charge attracts H2O molecules more strongly
So a stronger ion-dipole force is formed (stronger electrostatic attraction) which means more energy is released, we have a more negative value
So more likely to have an exothermic enthalpy of solution

Question 21

How does size of the ion affect enthalpy of solution?

Answer 21

Small ions have a larger charge density as the charge is spread out over a smaller area
So has stronger electrostatic attraction to water molecules
So more energy is released when these ion-dipole forces are made giving a more negative value so the enthalpy of solution is more likely to be exothermic

Question 22

Can enthalpies of solution be endothermic?

Answer 22

Yes they can take in more energy than they release