Adding Water to Cotton

1
(No Transcript)
2
Adding Water to Cotton

• Add a drop of water to cotton.
• What should happen??
• What did happen ?
• There is Sodium Peroxide on the Cotton. Lets
  write a balanced equation of the reaction with
  water.
• Na2O2(s) 2 H2O(l) ?
• 2 Na(aq) 2 OH-(aq) H2O2(aq)

3
Adding Water to Cotton

• Na2O2(s) 2 H2O(l) ? 2 Na(aq) 2 OH-(aq)
  H2O2(aq)
• OH- is a catalyst for the decomposition of
  hydrogen peroxide
• OH-
• 2 H2O2(aq) ? 2 H2O(l) O2(g)
• Why does cotton burn when water is added ??

4
Adding Water to Cotton

• DHreaction DHf(products) - DHf(reactants)
• Na2O2(s) 2 H2O(l) ? 2 Na(aq) 2 OH-(aq)
  H2O2(aq)
• DHreaction 2(-240 kJ/mol) 2(-230 kJ/mol)
  (-188 kJ/mol)
• (-511 kJ/mol) 2(286 kJ/mol)
• - 45 kJ/mol (mildy exothermic)

5
Adding Water to Cotton

• DHreaction DHf(products) - DHf(reactants)
• OH-
• 2 H2O2(aq) ? 2 H2O(l) O2(g)
• DHreaction 2(-286 kJ/mol) 0 2(188 kJ/mol)
• - 196 kJ/mol (very exothermic)

6
Adding Water to Cotton

• Combustion of a hydrocarbon (simplified problem)
• CH3CH2CH3 5 O2 ? 3 CO2 4 H2O
• DHreaction 3(-394 kJ/mol) 4(-286) (20
  kJ/mol) 0
• -2346 kJ/mol (extremely exothermic)

7
Adding Water to Cotton

• Combustion of cellulose (polysaccharide)

glucuose
C6H10O5 3 O2 ? 6 CO2 6 H2O
DHreaction 6(-394 kJ/mol) 6(-286 kJ/mol)
(1250 kJ/mol) 0 -2830
kJ/mol (extremely exothermic)
8
Combustion of Nitrocellulose
The Self-Lighting Candle
H2SO4 C12H22O11(s) ? 12 C(s) 11 H2O(g)
C 2 KClO3 (s) ? 2 KCl 3
O2(g)
C(s) O2(g) ? CO2(g)
Glucose nitrate DHf -860 kJ/mol NH3
DHf -46 kJ/mol CO2 DHf -394
kJ/mol
Sucrose DHf -860 kJ/mol H2O(g)
DHf -242 kJ/mol CO2(g) DHf
-394 kJ/mol KClO3(s) DHf -391
kJ/mol KCl(s) DHf -436 kJ/mol
What is heat of reaction?
What are the heats of reaction?
9
Combustion of Nitrocellulose
C9H9O12N3 ? 6 CO2 3 NH3
Glucose nitrate DHf -860 kJ/mol NH3
DHf -46 kJ/mol CO2 DHf -394
kJ/mol
What is heat of reaction?
DHf -1640 kJ/mol
10
The Self-Lighting Candle
H2SO4 C12H22O11(s) ? 12 C(s) 11 H2O(g)
C 2 KClO3 (s) ? 2 KCl 3
O2(g)
C(s) O2(g) ? CO2(g)
Sucrose DHf -860 kJ/mol H2O(g)
DHf -242 kJ/mol CO2(g) DHf
-394 kJ/mol KClO3(s) DHf -391
kJ/mol KCl(s) DHf -436 kJ/mol
What are the heats of reaction?
-3522 kJ/mol -90 kJ/mol -788 kJ/mol
11
The Self-Lighting Candle
What is burning??
The wax is burning.
C25H52(s) 38 O2 ? 25 CO2(g) 26 H2O(g)