Ethalpy Changes In Solution

Question 1

How to compounds dissolved in water?

Answer 1

Water molecules are able to break up the giant ionic lattice structure and overcome the strong electrostatic attractions between oppositely-charged ions.

Question 2

What is the standard enthalpy change of solution?

Answer 2

The enthalpy change that takes place when one mole of a solute dissolves in a solvent. If the solvent is water, the ions from the ionic lattice finish up surrounded with water molecules as aqueous ions. Can be exothermic or endothermic depending on the relative sizes of the lattice enthalpy and the enthalpy changes of hydration.

Question 3

What mass should be used in enthalpy calculations? (Q=mc x change in temperature)?

Answer 3

The mass of the solution and not the mass of the water.

Question 4

What two processes take place when a solid ionic compound dissolves?

Answer 4

• The ionic lattice breaks up.
• Water molecules are attracted to, and surround, the ions.

Question 5

What happens in these dissolving processes?

Answer 5

• The ionic lattice is broken up forming separate gaseous ions, this is the opposite energy change from the lattice energy, which forms the ionic lattice from/gaseous ions.
• The separate gaseous ions interact with the polar molecules to form hydrated aqueous ions. The energy change involved is called the enthalpy change of hydration.

Question 6

What is the enthalpy change of formation?

Answer 6

The enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions.