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Chem Eq Lec1
 

Chem Eq Lec1

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  • Mechanical, thermal, chemical equilibrium
  • Equilibrium is reached from either direction
  • magnitude

Chem Eq Lec1 Chem Eq Lec1 Presentation Transcript

  • Chemical Equilibrium
    Presentation Part 1
    c!e-γ˚T 2010
  • Equilibrium – “balance of force”
  • What is chemical equilibrium?
    • Kinetics deals with the rate of the reaction while Equilibrium deals with the extent in which the reaction proceeds.
    • A chemical reaction is capable of attaining equilibrium when it is a reversible process.
  • When is equilibrium reached?
    • Rateforward = Ratereverse
    • amount of R and P are constant
  • A reaction in equilibrium state
    • No observable change is seen after a certain time (dynamic process)
    • The ratio of the amount of product raised to its stoichiometric coefficient to the amount of reactants also raised to its stoichiometric coefficient remains constant at constant temperature.
  • k1
    CO(g) + 2 H2(g) CH3OH(g)
    k-1
    [CH3OH]
    [CH3OH]
    [CH3OH]
    [CO][H2]2
    [CO][H2]
    [CO](2[H2])
    14.2 M-2
    0.596 M-1
    1.19 M-1
    14.2 M-2
    1.09 M-1
    2.17 M-1
    14.2 M-2
    1.28 M-1
    2.55 M-1
  • Reaction Quotient (Q)
    • The ratio of the amount of product raised to its stoichiometric coefficient to the amount of reactants also raised to its stoichiometric coefficient at any point in the reaction is known as Reaction Quotient (Q)
    - The amount can be in terms of molar concentration or partial pressure
  • Equilibrium constant (KEQ)
    • When the amount present at equilibrium is the value used in Q, it becomes KEQ.
    Law of Mass Action
    - when a system reaches equilibrium at a given temperature, the ratio of the quantities that make up the reaction quotient has a constant numerical value, KEQ
  • KEQ from Rate Law
    The following equations show how KEQ expression can be derived from the Rateforward = Ratereverse.
     
    Forward reaction: N2O4 (g) 2 NO2 (g)
    Rate law: Rate = kf [N2O4]
    Reverse reaction: 2 NO2 (g) N2O4 (g)
    Rate law: Rate = kr [NO2]2
     
    Therefore, at equilibrium,
    Ratef = Rater
    kf [N2O4] = kr [NO2]2
    Rewriting, it becomes
  • Rules in writing KEQ and Q expression
    amounts is be expressed in terms of molar concentration (for both aqueous and gas) or partial pressure (gas).
    products are always in the numerator, and the reactants are always in the denominator
    Coefficients in the chemical equations are the exponents used in the expression
    The stoichiometric coefficient of each molecule or compound is used in place of the experimentally determined exponents because the reaction is assumed to occur at a fast reversible single step.
    solids and liquids are not included in the expression, why?
    unit less
  • Practice writing KCand KP expression for the following reactions:
    formation of ozone from oxygen gas
    formation of ammonia from nitrogen and hydrogen gas
    decomposition of phosphorus pentachloride into phosphorus trichloride and chlorine gas
    formation of sulphur trioxide from oxygen and sulphur dioxide
    reaction of the aqueous sodium carbonate and calcium chloride to form solid calcium carbonate and sodium chloride solution
    decomposition of solid calcium carbonate into lime and carbon dioxide