Expressing Concentration

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Expressing Concentration

• Solute the dissolved particles in a solution.
• Solvent the dissolving medium in a solution.

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Expressing Concentration

• Molarity (M) of moles of solute
• liters of
  solution
• Molarities are often expressed as a number within
  brackets 5.0 ? 5.0 M, or 5.0 moles/L.
• Molality (m) moles of solute moles
  solute
• kilogram of solvent
  1000 g of solvent
• Mole fraction Xa moles solute
  
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  Total moles of solute solvent

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EXAMPLE 1

• 45.0g of NaOH are dissolved in 4953g of water.
  Express the molarity, molality, and mole fraction
  of this NaOH solution.

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EXAMPLE 2

• Some students wish to make 800.0 mL of 5.50 M
  solution of sulfuric acid using dry sulfuric acid
  and water. What must they do?

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Communicating Equilibrium

• What is a concise way to communicate the degree
  toward which a state of equilibrium lies toward
  the reactants vs. the products?

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Equilibrium Constants

• Keq The ratio of product concentrations to
  reactant concentrations, with each concentration
  raised to a power given by the number of moles of
  that substance in the balanced chemical equation.

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Equilibrium Constant

• aA bB ? cC dD
• Keq Cc x Dd
• Aa x Bb
• If Keq gt1, products are favored at equilibrium
• If Keq lt1, reactants are favored at equilibrium.

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EXAMPLE 3

• Write an expression for the equilibrium constant
  for each of the following
• 4H2(g) CS2(g) ? CH4(g) 2H2S(g)
• 2NO(g) O2(g) ? 2NO2(g)

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EXAMPLE 4

• At high temperature, the following system reaches
  equilibrium
• N2(g) O2(g) ? 2NO(g)
• An analysis of the equilibrium mixture in a
  1.00-L flask gives the following results
  Nitrogen 0.50 mol oxygen 0.50 mol nitrogen
  monoxide 0.020 mol. Calculate Keq for this
  reaction.

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EXAMPLE 5

• At 750oC, the following system reaches
  equilibrium
• H2(g) CO2(g) ? H2O(g) CO(g)
• An analysis of the equilibrium mixture in a
  1.00-L flask gives the following results
  hydrogen 0.053 mol carbon dioxide 0.053 mol
  water 0.047 mol carbon monoxide 0.047 mol.
  Calculate Keq AND the change in free energy for
  this reaction.