Oceans 1: Enthalpy Changes

Question 1

How do u find enthalpy change

Answer 1

1. q ( J ) = mcAT ( need to divide answer by 1000 —-> kJ )
2. No. of mole of solute ( solid dissolving )

3 . Delta H = q/ n in kJmol^-1

Question 2

What does a +ve delta H show

Answer 2

Endothermic reaction

Question 3

What does a -ve delta H show

Answer 3

EXOthermic reaction

Question 4

Describe the enthalpy changes of solution of solution in the process of dissolving

Answer 4

1. Ions must be separated for in their lattice ( before ionic solid can dissolve ) = ENDOthermic
2. Energy needed depends on strength of lattice ( lattice ) enthalpy
3. Ions then hydrated = EXOthermic

Question 5

What are the enthalpy changes required for dissolving to take place

Answer 5

Energy released ( EXOthermic ) by bond formation is sufficient to compensate for energy required ( ENDOthermic ) to break bonds between ions

Question 6

lattice enthalpy = ???

Answer 6

Measure of strength of ionic bonding

Question 7

What does lattice enthalpy depend on

Answer 7

• charge density

• size of ion ( smaller = greater attraction)
• charge of ion ( higher charge = greater attraction)

Question 8

How does charge density effect lattice enthalpy

Answer 8

Greater charge density = lattice enthalpy morvr -ve ( EXOthermic ) = more energy given out

Question 9

Charge density = ???

Answer 9

Ratio of charge of an ion to its volume

Question 10

Describe what effects enthalpy of hydration ( basic same to lattice enthalpy )

Answer 10

More EXOthermic when:

• smaller ion
• higher charge

= greater charge density