22.2 enthalpy changes in solution

Question 1

define the standard enthalpy change of solution

Answer 1

the enthalpy change that takes place when one mole of solute dissolves in solvent

Question 2

write the equation for the enthalpy change if solution of sodium chloride in water

Answer 2

Na+Cl- + aq —-> Na+ + Cl-

Question 3

what is the attraction in solid NaCl?

Answer 3

Na+ and Cl- ions are attracted together in a giant ionic lattice

Question 4

what is the attraction in aqueous NaCl?

Answer 4

Na+ and Cl- are separate but now surrounded by water molecules

Question 5

what are the partial changes in water molecules attracted to in aqueous ions?

Answer 5

• oxygen atom is attracted to positive ion
  + hydrogen atoms are attracted to negative ion

Question 6

how do you calculate the enthalpy change of solution?

Answer 6

1) calculate energy change q in the solution in kJ
2) calculate the moles of the ionic compound that dissolved
3) calculate the enthalpy change of solution in kJ/mol

Question 7

what happens when the solid ionic compound dissolves in water?

Answer 7

the ionic lattice breaks up
water molecules are attracted to and surround the ions

Question 8

what are the two types of energy change that are involved in the dissolving process?

Answer 8

1) the ionic lattice is broken up forming separate gaseous ions (opposite energy change from lattice energy)
2) separate gaseous ions interact with polar water molecules to form hydrated aqueous ions (enthalpy change of hydration)

Question 9

define enthalpy change of hydration

Answer 9

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

Question 10

is the enthalpy change of solution endothermic or exothermic?

Answer 10

can be both depending on the relative sizes of the lattice enthalpy and the enthalpy changes of hydration