1. 4.7 Kw and the Ionization of Water
Chemistry 12

2. 2 H2O(l) + 59J ↔ H3O+(aq) + OH−(aq)
4.7
2 H2O(l) + 59J ↔ H3O+(aq) + OH−(aq)
Spontaneous
Not very often
Affected by temperature

3. 2 H2O(l) + 59J ↔ H3O+(aq) + OH− (aq)
4.7
2 H2O(l) + 59J ↔ H3O+(aq) + OH− (aq)
Kw expression and value?
Pure liquids (and solids) left out of Keq
Kw = [H3O+][OH−]

4. 4.7
Kw value?
Kw = 1.0×10−14
At 250C
p.334

5. 2 H2O(l) + 59J ↔ H3O+ (aq) + OH− (aq)
4.7
What happens to the value of Kw if the temperature of H2O is increased above 250C?
2 H2O(l) + 59J ↔ H3O+ (aq) + OH− (aq)
Increased temperature is a stress
 according to LCP, shift will be away from heat term
[H3O+] and[OH−] will increase
KW will increase

6. 4.7
What is the [H3O+] of pure water at 250C? Kw = [H3O+][OH−] = 1.0×10−14 [H3O+] = [OH−] [H3O+]2 = 1.0×10−14 [H3O+] = 1.0×10−14 = 1.0×10−7

7. Learning Check What is the ionization of water?
How do the [H3O+] and [OH-] compare in acidic, basic and neutral conditions?
What is Kw and how is it affected by temperature?
What is the value of Kw at 25C?
Can you calculate [H3O+] or [OH-] at 25C using Kw?

8. Read & Highlight Self Notes (p.1-2) Homework Hebden #28, 29
4.7
Read & Highlight Self Notes (p.1-2) Homework Hebden #28, 29