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Chemical equilibrium

This chapter explores the concept of chemical equilibrium, focusing on reversible reactions where neither reactants nor products are favored. Equilibrium occurs when the concentrations of reactants and products remain constant as the rates of the forward and reverse reactions equalize. The law of chemical equilibrium is discussed, including how to write equilibrium constant expressions and calculate their values. Additionally, factors affecting equilibrium, such as Le Chatelier's Principle, temperature, and pressure are examined alongside practical examples to solidify understanding. ###

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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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