22.2 Enthalpy changes in solution

Question 1

What is the symbol for standard enthaly change of solution?

Answer 1

Question 2

Definition of standard enthalpy change of solution

Answer 2

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

Question 3

Equation for the enthalpy change of solution of sodium chloride in water?

Answer 3

Question 4

What type of reaction is enthalpy change of solution?

Answer 4

Can be exothermic or endothermic

Question 5

How are ionic compounds/ lattices dissolved?

Answer 5

Water molecules are polar and so can break the giant ionic lattice structure by overcoming the strong electrostatic attraction between oppositely charged ions to form an aqueous solution. δ+ hydrogen in H20 and δ− oxygen are attracted to towards the positive and negative ions. δ+ hydrogen is attracted to negative ion (eg. Cl-) , δ− oxygen is attracted to positive ion (Na+)

Question 6

What are the steps for calculating enthalpy change of solution (ΔsolH)?

Answer 6

1. calculate mass of the overall solution (+ water solution)
2. calculate q=mcΔt
3. calculate the moles of solute dissolved in n (salt) mass/Mr (not water)
4. calculate ΔsolH = q/moles
   in kJmol-1

Question 7

Calculate the enthalpy change of solution for 6.40g of NH4NO3 dissolved in 25g of water. Temperature has decreased by 17.5

Answer 7

+28.7 kJmol -1

Question 8

Calculate the enthalpy change of solution for 3g of NaOH dissolved in 50g of water. Temperature has increased by 14 degrees

Answer 8

-41.4 kJmol-1

Question 9

What energy changes take place when a solid ionic compound is dissolved in water?

Answer 9

1. the ionic lattice is broken up forming separate gaseous ions
   = endothermic (s) to (g)
   2.the separate gaseous ions interact with polar water molecules to form hydrated aqueous ions (enthalpy change of hydration
   = exothermic

Question 10

What is the symbol for enthalpy change of hydration?

Answer 10

ΔhydH

Question 11

Definition of enthalpy change of hydration (ΔhydH)

Answer 11

The enthalpy change that accompanies the dissolving of gaseous ions in water to form 1 mole of aqueous ions

Question 12

Contract an energy cycle and calculate the lattice enthalpy of sodium chloride

Answer 12

Question 13

Construct an energy cycle and calculate the enthalpy change of hydration for Ca2+ ions

Answer 13