Chapter 22 Key Concepts

Question 1

why is the second electron affinity endothermic?

Answer 1

second electron is gained by a negative ion which repels the electron away. Energy needed to force the negatively charged electron onto a negative ions.

Question 2

what happens when a salt dissolves in water

Answer 2

-ionic lattice breaks up
opposite to LE . youre forming sperate gas ions
-water molecules are attracted to and surround the ions
separate gas ions interact with polar water molecules to form hydrated aq ions. this is the enthalpy change of hydration

Question 3

factors affecting lattice enthalpy and hydration

Answer 3

charge density. this is split into ionic size and ionic charge.

Question 4

whats the effect of decreasing ionic size on lattice enthalpy

Answer 4

ionic radius decrease
attraction between ions increase
lattice enthalpy more negative
melting point increases

Question 5

whats the effect of increasing ionic charge on lattice enthalpy

Answer 5

ioinc charge increases
attraction between ions increase
lattice enthaply becomes more negative
melting point increases

*regardless of moles

Question 6

describe the effect of ionic charge and size from sodium to aluminium

Answer 6

ioinic radius decreases
-ionic size decreases so more attraction to oppositely charged ions
ionic charge increases
-more attraction to oppositely charged ions

Question 7

describe the effect of ionic charge and size from chlorine to sulfur

Answer 7

increasing charge means greater attraction oppositely charged ions
increasing ionic size means less attraction to oppositely charged ions

Question 8

uses of stable ionic compounds with high lattice enthalpies eg MgO Al2O3 and ZnO3

Answer 8

inside coating of furnaces and refractories.

jewels like rubies and sappharies are made long lasting by Al Oxide

Question 9

effect of increasing ionic size of hydration

Answer 9

ionic radius increases
attraction between ions and water molecules decreases
hydration less negative

Question 10

effect of decreases ionic charge of hydration

Answer 10

• ionic charge decreases
• attraction between ions and water molecules decreases
• hydration less negative

Question 11

what condition to do with enthalpy must be met for an ionic compound to dissolve? also what else must we consider?

Answer 11

sum of hydration must be greater than lattice enthalpy

• enthalpy change of solution will be exo and the thing should dissolve.
• endothermic enthalpy changes of solution dissolve too. so solubility also depends on temperature and entropy

Question 12

what state has the greatest entropy

Answer 12

gaseous state

Question 13

limitations of gibbs

Answer 13

• doesn’t consider the kinetics or rate of reaction. just considers thermodynamic feasibility
• some reactions may have large activation energy so the reaction would take place slowly if at all.