Basics of Chromatography Separation of Analytes Type of Equilibrium.
EQUILIBRIUM BASICS
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Transcript of EQUILIBRIUM BASICS
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EQUILIBRIUM BASICSChapter 14.1-14.3
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Lesson ObjectivesKnow -Factors that affect/don’t affect a reaction reaching equilibrium
-K is equilibrium constant for any reversible reaction-Kc and Kp are related to each other through Kp = Kc(RT)Dng
-Coefficient Rule-Reciprocal Rule-Rule of Multiple Equilibria
Understand -Equilibrium is based on when RATES of forward and reverse reactions are equal, not when concentrations of reactants and products are equal-The equilibrium constant K has its roots in the kinetics rate law constant k-The size of the equilibrium constant tells us which side (reactants or products) is favored in an equilibrium reaction-K may only be calculated with concentration or pressure values when the system is at EQUILIBRIUM-Solids and liquids are not used in equilibrium constant expressions
Do -Write an equilibrium constant expression for a given reaction-Calculate K based on equilibrium concentrations-Apply the Coefficient Rule, the Reciprocal Rule, and the Rule of Multiple Equilibria to calculate a new K from a known K-Calculate K when given initial concentration or pressure values (ICE Chart)
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Which of the following is NOT true about a reaction at equilibrium?
N2O4 2NO2
A. [N2O4] = 2 [NO2]B. The rate of the forward and reverse reactions
are the sameC. The equilibrium constant will describe whether
the process favors reactants or productsD. [N2O4] and [NO2] remain constant.E. For every 2 molecules of NO2 reacted, 1
molecule of N2O4 is produced
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AT EQUILIBRIUM
Two reactions are occurring (forward and reverse) indicated by double arrow.
Equilibrium definition: a reaction has reached equilibrium (balance) when the forward and reverse reactions occur at the same RATE.
This means that concentrations of reactants and products stay CONSTANT over time
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An Equilibrium Example
See this interactive tutorial here
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Equilibrium factors:
Equilibrium IS dependent on◦TEMPERATURE (affects the equilibrium
constant, K)
It is NOT dependent on◦Original concentrations◦Volume of the container◦Total pressure of the system
Remember – the partial pressure of a gas in a mixture is proportional to the mole fraction of that gas in the mixture!
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The following data are for the system A(g) 2B(g)
Time (s) 0 20 40 60 80 100
PA (atm) 1.00 0.83 0.72 0.65 0.62 0.62
PB (atm) 0.00 0.34 0.56 0.70 0.76 0.76
How long does it take the system to reach equilibrium?
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K: equilibrium constantTells us the extent to which the reaction will go
until it reaches equilibrium◦Large K means the reaction goes mostly to product◦Small K means the reaction stays mostly as reactant
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For a reaction2A(g) + B(g) 2C(g) K = 1 x 1083
which of the following can be concluded?
A. At equilibrium, [A] = ½[B] = [C]B. At equilibrium, the largest concentration is [A]C. At equilibrium, the largest concentration is [C]D. This reaction favors the reactantsE. This reaction happens very quickly
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Writing K expression (equilibrium expression)
Uses only gaseous or aqueous products and reactants (no solids or liquids; their concentrations do not change during reactions)
Coefficients become exponentsProducts over reactantsFor aA + bB cC + dD
Kp = or Kc =
Relate to each other: Kp = Kc(RT)Δng
◦R = gas law constant (0.0821 atm·L/mol·K)◦Δng = change in moles of gas (products – reactants)
(PC)c x (PD)d
(PA)a x (PB)b
[C]c [D]d
[A]a [B]b
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Which of the following species should NOT be included in the equilibrium constant expression for the reaction?2A(s) + B(aq) 2C(l) + D(g)
A. A, B, CB. B, CC. A, CD. A, C, DE. B, D
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For a reaction 2A + B 2CWhen equilibrium is established, the ratio of products to reactants (K) = 0.5. Which of the following initial conditions could be changed to cause a different equilibrium constant value?
A. Start with more AB. Dilute the reaction by adding waterC. Increase the temperature of the reactionD. Add a catalyst
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To calculate Kp from Kc for the reactionA(g) + 2B(g) C(g)what would be the exponent to which Kc(RT) is raised?
A. -2B. -1C. 0D. 1E. 2
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Write the equilibrium constant (K) expressions
for the following reactions:
I2(g) + 5F2(g) 2 IF5(g)
SnO2(s) + 2H2(g) Sn(s) + 2H2O(l)
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For the reaction2 NO(g) + O2(g) 2 NO2(g)determine the Kp at 298K if Kc is 4.67 x 1013
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True or False?Given the equation below,
N2 + 3H2 2 NH3
if one mole of N2 is mixed with 3 moles of H2, 2 moles of NH3 will form.
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True or False?Given the equation below,
N2 + 3H2 2 NH3
for every 1 mole of N2 that reacts, 3 moles of H2 will also react and 2 moles of NH3 will form.
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Calculate K for the reactionNH4CO2NH2(s) 2 NH3(g) + CO2(g) if at equilibrium there are 0.159 g of NH4CO2NH2 and pressures of 0.0451 atm of CO2 and 0.0961 atm NH3
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K depends on the form (coefficients) of the balanced equation! This means that K changes when: ◦The coefficients are multiplied◦Reactions are reversed◦Reactions are added together (mechanism)
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Coefficient rule: If coefficients are multiplied by a factor (n),
then K is RAISED TO THE (n) EXPONENTA2 (g) + 2B (g) 2AB (g)
K =
3A2 (g) + 6B (g) 6AB (g)
K =
PAB2
PA x PB2
PAB6
PA3 x PB
6
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Calculate K for the formation of 2 moles of ICl(g)ICl (g) ½I2 (g) + ½Cl2 (g) K = 2.2x10-3
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Reciprocal rule: If the reaction is reversed, K of the forward
and K of the reverse are reciprocals of each other (new K = 1/old K)
A2 (g) + 2B (g) 2AB (g)
K =
2AB (g) A2 (g) + 2B (g)
K =
PAB2
PA x PB2
PAB2
PA x PB2
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Rule of multiple equilibria
If multiple reactions are added together to get an overall reaction, the overall K is the PRODUCT of the individual K’s
A2 (g) + 2B (g) 2AB (g)2AB (g) + C (g) A2B2C (g)
A2 (g) + 2B (g) + C (g) A2B2C (g)
Find overall K it by multiplying individual K’s:
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Given the reactions below and their constants, calculate K for the rxn:Fe(s) + H2O(g) FeO(s) + H2(g)
H2O(g) + CO(g) H2(g) + CO2(g) K = 1.6FeO(s) + CO(g) Fe(s) + CO2(g) K = 0.67
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Determining KK must use values AT EQUILIBRIUM!
When given initial concentrations or pressures in a problem , you must determine what the values will be at equilibrium before you can calculate K
Use an ICE Chart to determine how the initial values will increase or decrease to get to equilibrium, then solve for K.◦ Solids and liquids have no effect on equilibrium, so they
don’t need values in your ICE chart.
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The ICE ChartInitial/Change/EquilibriumGiven initial pressures, find equilibrium constant
A2 = 0.1 atmB = 0.2 atmA2(g) + 2B(g) 2AB(g)
ICE
0.1 atm 0.2 atm 0.0 atm-x -2x +2x
0.1 - x 0.2 - 2x 2x
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For the decomposition reactionNH4HS(s) NH3(g) + H2S(g)
In a sealed flask are 10.0 g of NH4HS, NH3 with a partial pressure of 0.692 atm and H2S with a partial pressure of 0.0532 atm. When equilibrium is established, it is found that the partial pressure of NH3 has increased by 12.4%. Calculate K for this reaction.
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Lesson ObjectivesKnow -Factors that affect/don’t affect a reaction reaching equilibrium
-K is equilibrium constant for any reversible reaction-Kc and Kp are related to each other through Kp = Kc(RT)Dng
-Coefficient Rule-Reciprocal Rule-Rule of Multiple Equilibria
Understand -Equilibrium is based on when RATES of forward and reverse reactions are equal, not when concentrations of reactants and products are equal-The equilibrium constant K has its roots in the kinetics rate law constant k-The size of the equilibrium constant tells us which side (reactants or products) is favored in an equilibrium reaction-K may only be calculated with concentration or pressure values when the system is at EQUILIBRIUM-Solids and liquids are not used in equilibrium constant expressions
Do -Write an equilibrium constant expression for a given reaction-Calculate K based on equilibrium concentrations-Apply the Coefficient Rule, the Reciprocal Rule, and the Rule of Multiple Equilibria to calculate a new K from a known K-Calculate K when given initial concentration or pressure values (ICE Chart)