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Chemical equilibrium

Chemical equilibrium. Chapter 17. Reversible Reactions. Most reactions do not proceed to completion. N 2 (g) + H 2 (g)  2NH 3 (g) 2NH 3 (g)  N 2 (g) + H 2 (g). What is Equilibrium.

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Chemical equilibrium

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  1. Chemical equilibrium Chapter 17

  2. Reversible Reactions • Most reactions do not proceed to completion. • N2(g) + H2(g)  2NH3(g) • 2NH3(g)  N2(g) + H2(g)

  3. What is Equilibrium • Equilibrium is when the concentrations of the reactants and products of a chemical reaction are constant. • Chemical equilibrium happens when the rate of the forward reaction is equal to the rate of the reverse reaction.

  4. Law of Chemical Equilibrium • aA + bBcC + dD • The equilibrium constant expression: • If Keq > 1 the products are favored • If Keq < 1 the reactants are favored

  5. Types of Equilibrium • Homogeneous: • CO2(g)  2CO(g) + O2(g) • Heterogeneous: • H2O(l)  H2O(g) • CaCO3(s) CaO(s) + CO2(g)

  6. Write the equilibrium constant expression fo the following reactions • N2(g) + H2(g)  2NH3(g) • N2O4(g)  2NO2(g) • 2H2S(g)  2H2(g) + S2(g) • CO(g) + 3H3(g)  CH4(g) + H2O(g) • 4NH3(g) + 5O2(g)  4NO(g) + 6H2O(g)

  7. Equilibrium Constants • When equilibrium is reached the concentrations of the reactants and the products will not change. • At any given temperature the value of keq will always be the same no matter what the equilibrium concentrations are.

  8. Practice • Calculate the value of keq for the following reaction and concentrations. • N2 + 3H2 2NH3 • [N2] = 0.533 M • [H2] = 1.600 M • [NH3] = 0.933 M • 0.399

  9. Calculate keq for the reaction: • N2O4(g)  2NO2(g) If [N2O4] = 0.0185 mol/L and [NO2] = 0.0627 mol/L • Calculate keq for the reaction • CO(g) + 3H2(g)  CH4(g) + H2O(g) if [CO] = 0.0613 mol/L, [H2] = 0.1839 mol/L, [CH4] = 0.0387 mol/L and [H2O] = 0.0387 mol/L • For the reaction COCl2(g) CO(g) + Cl2(g)

  10. Factors Affecting Equilibrium • The by-products of an industrial process are CO and H2. These two gasses can combine to produce CH4 and H2O in equilibrium. • Use the following data to find keq for this reaction. • [CO] = 0.300M, [H2] = 0.100M, [CH4] = 0.059 M, [H2O] = 0.020 M • The chemists in charge of this industrial process would like to make use of the methane (CH4) that is being produced. In order for them to have a usable amount of methane the concentration must be 0.100 M or higher. How can they achieve this?

  11. Le Chatelier’s Principle • If a stress is applied to a system at equilibrium, the system will shift in the direction that relieves that stress. • Suppose additional CO is injected into the reaction vessel of the industrial process we discussed. How would this affect the equilibrium of the system?

  12. Le Chatelier’s Principle • Along with adding reactants or removing products, what other stresses can we apply to a system? • Temperature • Pressure

  13. Calculating Equilibrium Concentrations • The reaction: • CO(g) + 3 H2(g)  CH4(g) + H2O(g) • Has a Keq of 3.933 at 1200 K. • If the [CO] = 0.850 M, [H2] = 1.33 M, and [H2O]= 0.286 M, what is the concentration of CH4?

  14. Solubility Product Constant • Some ionic compounds dissolve completely in water. • Ex: NaCl(aq) Na+(aq) + Cl-(aq) • Some ionic compounds do not dissolve completely in water. • Ex: BaSO4(s)  Ba2+(aq) + SO42-(aq) • This process is happening in equilibrium. • So there is an equilibrium constant associated with it.

  15. Calculate the solubility of AgI(s). • ksp = 8.5 x 10-17

  16. Examples • Calculate the solubility in mol/L of CuCO3 if it’s ksp is 2.5 x 10-10 • 1.6 x 10-5 mol/L • Calculate the solubility PbCrO4 if it’s ksp is 2.3x10-13. • 4.8 x 10-7 mol/L • Calculate the solubility of CaF2 if it’s ksp is 3.5x10-11. • 4.18x10-6 mol/L

  17. Calculating Ion Concentrations • Sometimes the concentrations of the ions are not the same as the solubility. • Mg(OH)2(s)  Mg2+(aq) + 2OH-(aq) • ksp = 5.6 x 10-12

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