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Adding Water to Cotton

Adding Water to Cotton. Add a drop of water to cotton. What should happen?? What did happen ? There is Sodium Peroxide on the Cotton. Let’s write a balanced equation of the reaction with water. Na 2 O 2 (s) + 2 H 2 O(l) → 2 Na + (aq) + 2 OH - (aq) + H 2 O 2 (aq).

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Adding Water to Cotton

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

  2. 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 ??

  3. 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)

  4. 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)

  5. 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)

  6. 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)

  7. The Self-Lighting Candle Combustion of Nitrocellulose 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 NH3DHf°= -46 kJ/mol CO2DHf°= -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?

  8. Combustion of Nitrocellulose C9H9O12N3→ 6 CO2 + 3 NH3 Glucose nitrate DHf°= -860 kJ/mol NH3DHf°= -46 kJ/mol CO2DHf°= -394 kJ/mol What is heat of reaction? DHf°= -1640 kJ/mol

  9. 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

  10. The Self-Lighting Candle What is burning?? The wax is burning. C25H52(s) + 38 O2→ 25 CO2(g) + 26 H2O(g)

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