Chapter 13 Textbook

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DesLee26
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Chapter 13 Textbook
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2013-03-24 19:01:54
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CHM 112
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Dr. C
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  1. chemical equilibrium
    the state reached when the concentrations of reactants and products remain constant over time
  2. When a liquid evaporates in a closed container, it soon gives rise to a constant __ because of a dynamic equilibrium in which the number of molecules leaving and entering are the same
    vapor pressure
  3. A mixture of reactants and products in the equiblibrium state is called an __
    equilibrium mixture
  4. True or False:
    All reactions go to completion
    • False:
    • Many dont
  5. True or False:
    All chemical reactions are reversible.
    True
  6. Why do we call reactions inrreversible if all are reversible?
    they proceed nearly to completion, so that the equilibrium mixture contains almost all products and almost no reactants
  7. equilibrium equation
    • equation that states the relation of the concentrations in an equilibrium mixture
    • Kc is hte equilibrium constant and the expression on the right is the equilibrium constant expression
    • Kc= [C]c [D]d/ [A]a[B]b
  8. The substances in the equilibrium constant expression may be __ or __ and __ in a solution, but may no tbe __.
    • ions in a solution
    • gases or molecuels
    • pure liquids
    • pure solids
  9. The equilibrium equation is also known as the __ because in hte early days of chemistry, concentration was called __.
    • law of mass action
    • "active mass"
  10. equilibrium constant Kc
    obtained by multiplying hte equilibrium concentrations of all the products and dividing by the producto f the equilibrium concentrations of all the reactants, with the concentration of each substance raised to the power of its coefficient in the balanced chem equaiton
  11. No matter what the individual equilibrium concentrations may be in a particular experiment, the equilibrium constant for a reaction at a particular temperature __.
    always has the same value
  12. units of Kc
    none ecuase they're ratios
  13. If we reverse the reaction, what happens to Kc?
    • it becomes 1/Kc
    • the prime in Kc' distinguishes this reaction
  14. Because gas pressures are easily measured, equilibrium equations for gas phase reactions are often written using __ rather than __.
    • partial pressures 
    • molar concentrations
  15. Values of Kp are __ because the partial pressures in the equilibrium equation are actually ratios of partial pressures in atmospheres to the __ of 1 atm.
    • dimensionless
    • standard-state partial pressure
  16. How are Kp and Kc related?
    the pressure of each component in a mixture of ideal gases is directly proportional to its molar concentration
  17. Euation for relation between Kp and Kc.
    • Kp= Kc (RT)deltan
    • R= 0.08206 Latm/ molK
    • deltan = (c+d)-(a+b) (number of moles= products-reactants)
  18. In general, Kp equals Kc only if the __.
    same number of moles of gas appear on both sides of hte balanced chem equation so that deltan=0
  19. Homogeneous equilibriu
    all reactants and products are in singlephase
  20. heterogeneous equilibria
    those in which reactants and products are present in more than one phase
  21. BEcause the standard state of a pure solid is __, the concentration ratio for a pure solid (and pure liquid) is equal to __. Thus, they equal 1 and can __.
    • the pure solid itself
    • one
    • be mitted from the equilibrium equation
  22. As a general rule, teh concentratiosn of pure solids and pure liquids are __.
    not included when writing an equilibrium equation
  23. Why do we include only the concentrations of gases and concentrations of solutes in solutions?
    because only thsoe concentrations can be varied
  24. If the temperature is changed, what happens to the concentration of pressure/
    will also change because the values of kc and Kp depend on temperature
  25. What does knowing the value of the equilibrium constant for a chemical reaction let us judge?
    the extent of the reaction, predict the direction of hte reaciton, and calculate equilibrium concentrations from initial concentrations
  26. What does a very large value of Kc mean?
    the equilibrium ratio of products to reactants is very large
  27. What does a very small value of Kc mean?
    the ratio of products to reactants is very small and the reaction proceeds hardly at all
  28. reaction quotient
    Qc= (same as equilibrium constant, except not necessrily equilibrium values)
  29. Whtat is one of the main goals of chemical synthesis?
    to maximize the conversion of reactants to products while minimizing the expenditure of energy
  30. If the reaction gives an equilibrium mixture that is rich in reactants and poor in products, however, then what?
    the experimental conditions must be adjusted
  31. Several factors can be exploited to alter the composition of an equilibrium mixture?
    • the concentration of reactants or products can be changed
    • the pressure and volume can be changed
    • the temperature can be changed
  32. TRUE OR FALSE:
    A catalyst affects the equilibrium concentraitons.
    false; does not
  33. What is Le Chatelier's Principle
    If a stress is applied to a reaction mixture at equilibrium, net reaction occurs in the direction that relieves the stress
  34. What does stress imply?
    change in concentration, pressure, volume, or tmeperature that disturbs the original equilibrium
  35. What does Le Chatelier's Principle predict when an equilibrium is disturbed by the addition or removal of any reactant or product?
    • the concentration stress of an added reactant or product is relieved by net reaction in the direction that consumes the added substance
    • the concentration stress of aremoved reactant or product is relieved by net reaction in the direction that replenishes the removed substance
  36. If Qc must increase, what must we do?
    increase the numerator (product) and decrease the denominator (reactant)
  37. What happens to the composition of the equilibrium mixture if we increase the pressure by decreasing the volume?
    according to Le Chatelier's principle, net reaction will occur in the direction that relieves the stress of the increased pressure, which means that the number of moles of gas must decrease
  38. What does Le Chatelier's principle predict (in terms of pressure)?
    • an increase in pressure by reducing the volume will bring about net reaction in the direction that decreases the number of moles of gas
    • a decrease in pressure by expanding the volume will bring about net reaction in the direction that incresaes the number of moles of gas
  39. True or False:
    The composition of an equilibrium mixture is unaffected by a change in pressure if the reaction involves no change in the number of moles of gas.
    True
  40. In applying Le Chatelier's principle to a heterogeneous equilibrium, the effect of pressure changes on solids and liquids can __.
    be ingnored because the volume of a solid or a liquid is nearly independent of pressure
  41. What happens if we keep the volume constant but increase the total pressure by adding a gas that is not involved in the reaction?
    The equilibrium remains undisturbed because adding an inert gas at constant volume doesn't change the partial pressures or the molar concentrations of the substances involved in the reaction. Only if the added gas is a reactant or product does the reaction quotient change
  42. True or False: As long as the temperature remains constant, however, concentration, pressure, or volume changes don't change the value of the equilibrium constant.
    True
  43. True or False: A change in temp never changes the value of the equilibrium constant.
    • False
    • almost always
  44. The equilibrium constnat for an exothermic reaction...
    • (negative delta h)
    • decreases as the temp increases
  45. The equilibrium constnat for an endothermic reaction...
    • (positive delta H)
    • increases as the tempearture increases
  46. If heat is added to an equilibrium mixture, thus increasing temp, net reaction occurs where?
    in the direction that relieves hte stress of the added heat.
  47. Even though a catalyst doesn't change the position of an equilibrium, it can significantly influence what?
    the choice of optimum conditions for a reaction
  48. The equilibrium constant can be simply
    the ratio of the rate constants for hte forward and reverse reactions
  49. What is the link between chemical equilibrium and chemical kinetics
    the relative values of the rate constants for the forward and reverse reactions determine the composition of the equilibrium mixture
  50. When kf is much larger than kr, what up with kc?
    Such a reaction is said to be...
    • it is very large adn the reaction goes almost to competion
    • irreversible
  51. In generatl, the forward and reverse reactions have different values of the __, so kf nad kr increase by different amoutns as temp increases.
    Ea
  52. For an exothermic reaction, Ea for the __ is greater than Ea for the __.
    • reverse
    • forward

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