05c reversible reactions


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05c reversible reactions

  1. 1. byby CHEMISTRY DEPARTMENTCHEMISTRY DEPARTMENT CHEM-111CHEM-111 General ChemistryGeneral Chemistry Unit five( d)Unit five( d) Reversible ReactionsReversible Reactions
  2. 2. Energy in Chemical Reaction Activation Energy When molecules collide, bond between atoms are broken and new bonds are formed. The energy needed to break apart those bonds is called the activation energy. If energy of a collision is less than the activation energy, the molecules bounce apart without reacting.
  3. 3. Progress of reaction Progress of reaction Energy Energy --------------- --------------------- ------- --------- Exothermic reaction Endothermic reaction Activation energy Energy of reactant Energy of products Heat of reaction (released) Activation energy Energy of reactant Energy of products Heat of reaction (absorbed) Exothermic and Endothermic Reaction Exothermic Reaction Energy of Product is lower than Energy of Reactant Endothermic Reaction Energy of Product is higher than Energy of Reactant
  4. 4. Rate of Reaction The rate or speed of reaction is measured by the amount of reactant used up, or the amount of product formed, in a certain period of time. Rate of reaction can be affected by : 1. Change in the temperature At higher temperature kinetic energy of reactants increases so they move faster and collide often 2. The amount of reactants in the container There are more collisions in reactants if amount is more 3. The addition of catalyst Catalyst lowers the activation energy
  5. 5. ----------------- ---------------------------- ----------------- Products Reactants Activation energy Activation energy for catalyzed reaction Energy Progress of reaction Hb + O2 HbO2 Hemoglobin Oxygen Oxyhemoglobin if patient having difficulty breathing may be given a breathing mixture with a higher oxygen content than the atmosphere. The Rate of Reaction Increases When Reactants are Added Patient can breathe more easily
  6. 6. Reversible Reactions When a reaction occurs both forward and reverse direction it is called reversible reaction (In many reactions the products interact and revert back into the reactants) 2SO2(g) + O2 ( g) 2 SO3(g) COCl2 CO (g) + Cl2 N2(g) + O2(g) 2NO(g) Chemical Equilibrium At Chemical Equilibrium Rate of Forward Reaction Becomes Equal to Rate of Backward Reaction
  7. 7. SO2 + O2 2SO2 + O2 2SO3 SO3 initially(at equilibrium) Chemical Equilibrium initially The same reaction mixture is obtained whether the reaction starts with the reactants or with just the products Sample-I Sample-II At equilibrium both samples have same proportions of reactants and products.
  8. 8. Reactants Product Reactants SO2 O2 SO2 SO3 O2 Reaction Chemical Equilibrium The equilibrium favors the formation of product SO3 The reaction of SO2 and O2 Amount in 1 liter Initial contents Equilibrium contents 2SO2(g) + O2 ( g) 2 SO3(g)
  9. 9. Reactant Reactant Reaction CO Cl2 COCl2COCl2 Product Chemical Equilibrium At equilibrium, the reaction favors the reactant because the reaction mixture at equilibrium contains mostly COCl2 COCl2 CO + Cl2 Initial contents Equilibrium contents Amount in 1 liter
  10. 10. Le Chatelier’s principle The rate of forward and reversed reaction will change to relieve the stress Effect of Changes on Equilibrium Factor Change (stress) Reaction Favored to Remove Stress Concentration Add more reactant Forward Remove reactant Reverse Add product Reverse Remove product Forward Temperature (T) Raise T of endothermic reaction Forward Lower T of endothermic reaction Reverse Raise T of exothermic reaction Reverse Lower T of exothermic reaction Forward
  11. 11. 1. Classify the following as exothermic or endothermic reactions: a. C3H8 + 5O2 3CO2 + 4H2O + 531 Kcal b. 2Na + Cl2 2NaCl + 196 Kcal c. PCl5 + 16 Kcal PCl3 + Cl2 d. Ca(OH)2 + 15.6 Kcal CaO + H2O Exercise