15.1.2 The Law of Mass Action and Types of Equilibrium Flashcards Preview

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Flashcards in 15.1.2 The Law of Mass Action and Types of Equilibrium Deck (12)
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1
Q

The Law of Mass Action and Types of Equilibrium

A
  • For a general reaction aA + bB -> cC + dD, the value of K c is constant at a given temperature.
    • Other forms of the equilibrium constant include the acid-dissociation constant and the solubility product constant.
2
Q

note

A
  • Review: Hydrogen reacts with iodine to form hydrogen
    iodide. Equilibrium is established after a period of time.
    More iodine is added to the system, and a new equilibrium is established.
  • When a system is in equilibrium, the components are not necessarily present in equal concentrations. The system is in equilibrium when there is no longer any net change in the amount of reactants or products.
  • The equilibrium constant (K c ) for a general equation, such as the one on the left, can be calculated by raising the molar concentrations of products to the power of their stoichiometric coefficients and dividing by the molar concentrations of reactants raised to the power of their stoichiometric coefficients.
  • According to the law of mass action, the values of K c are constant for a particular reaction at a given temperature.
  • The dissociation of a weak acid is an equilibrium for which an equilibrium constant can be written. Since the water is a liquid, its concentration is constant at a given temperature. Factoring out the concentration of water yields the acid-dissociation constant (K a ).
  • In a saturated solution, a salt (such as calcium fluoride, CaF 2 ) dissociates into ions and the ions come together to form the salt. This exchange happens at the same rate, so this is a dynamic equilibrium. Since the “concentration” (the density) of the solid CaF 2 is constant at a given temperature, the concentration of CaF 2 is factored out, yielding the solubility product constant (K sp ).
  • In a heterogeneous equilibrium, the components are in more than one phase of matter. The reaction between gold(III) ions (Au 3+ ) and copper metal (Cu) to form gold metal (Au) and copper(II) ions (Cu 2+ ) is a heterogeneous equilibrium. K het is the equilibrium constant describing this reaction.
3
Q

What is the equilibrium expression for the following reaction?
Mn(OH)2 (s) ->

A

Ksp = [ Mn2+ ] [OH − ]^2

4
Q

Is the following statement true or false?

In general, once equilibrium is achieved, the rates of the forward and the backward reactions are equal and so are the amount of reactants and products.

A

false

5
Q

Lead sulfate is a salt that is partially soluble in water. If the Ksp value for lead sulfate (PbSO4) is 1.3*10^-8, what are the concentrations of lead ions and sulfate ions in the solution? Assume PbSO4 is the only solute in the solution

A

[Pb2+] = [SO42-]= 1.1*10^-4

6
Q

When sulfur dioxide is passed over calcium oxide, it combines with CaO to form CaSO3. This is one of the ways sulfur dioxide can be removed from a gas mixture. The reaction taking place is as follows: CaO(s) + SO2(g) ->

A

Kc = 1 / [SO2 ]

7
Q

NH4SH, placed in a vessel at 22 degrees C, decomposes to form NH3 and H2S
NH4SH(s) ->

A

[NH3] = [H2S] = 1.1 * 10^-2

8
Q

After equilibrium is achieved in a homogenous gaseous reaction, it is changed by adding more reactants. This results in a new equilibrium. How is the equilibrium constant of the new equilibrium related to the old equilibrium constant value?

A

The new equilibrium constant value is the same as the old one.

9
Q

Gold ions react with copper metal to give gold metal and cupric ions
2Au3+ (aq) + 3Cu(s) ->

A

Keq = [Cu2+]^3/[Au3+]^2

10
Q

What is the equilibrium expression for the following reaction in aqueous solution?
Ag+(aq) + 2NH3(aq) ->

A

K = [Ag(NH3)2+]/([Ag+][NH3])^2)

11
Q

Consider the following reaction:

2NaHSO3(s) ->

A

remains unaffected

12
Q

What is the equilibrium expression for the following equilibrium?
Al3+(aq) + H2O(l) ->

A

k = [H+][AlOH2+]/[Al3+]

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