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Unit 4: Introduction to Chemical Equilibrium
Unit 4 goes over Equilibrium Terms, the Equilibrium Constant, Le Chatelier's Principle, and basic Acids and Bases
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Equilibrium Constant, K• Value obtained from the mathematical combination of equilibrium concentrations using
equilibrium law expression
Equilibrium Law Expression
• When the equilibrium concentrations are arranged into the following ratio, the resulting value is
always the same no matter what combination of initial concentration are used.
aAtbB Fact DD
c
e C
d_D b
Where A B C and Dare gasses or
A B aqueous solutions
Homogenous Equilibria
• All entities are in the same phase
Heterogenous equilibria
• Reactants and products are in more than one phase.
Problem 1:
• Write the equilibrium law expression for the reaction in which nitrogen gas reacts with hydrogen
gas in a closed system to produce gaseous ammonia as the only product.
Nz t 3He F 2MHz
NHz
K 3
Nz Ha
,Problem 2:
• Calculate the value of the equilibrium constant for the decomposition of ammonia at 500˚C into its
elements. The equilibrium concentrations are
1.50 10 5 no 11L
Nz
He 3.45 10 moth
g
NHzcgD 2.00 10 mom
2MHz T
g Nagy t 3Hug
1
1.50 10 5 3.45 10
k 2.00 10 4
2
15.40
• K is written with concentration of gasses and aqueous solutions only.
EX 2420cg F 242cg t 02cg
Z
Ke Hugs 02cg
• Equilibrium law expressions are always written from net ionic reactions
◦Ex: Consider the reaction of Zinc in Copper (II) chloride solution
• Step 1: Write a balanced chemical equation.
Zincs t Cadcaq Cues t ZnClacaq
• Step 2: Write total ionic equation
◦All aqueous compounds are separated into ions.
zincs t CaZtcaq t 2 g I Cucsst 2h24am t 241
Taq
, • Step 3: condense to net ionic equation
2nZtcaq
2ms t Cultcaq Cues t 2n2tcaq
k citcaq
• K depends on / changes with temperature and concentration
• K’ represents the reverse reaction: K = 1/K’
Nags t 311cg T 2NH3cg
2
K NHz K CNug.DEtzcg
jHgD3 NHzJ2
• The magnitude of K relates to the position of the reactants and products at equilibrium
• K >> 1
◦The reaction proceeds towards completion; Concentration of products is much greater than
the reactants
• K=1
◦Concentrations of products and reactants is about equal
• K << 1
◦Vert little product is formed; concentration of reactants is much greater than products
HW
Pg 442 #1
444 #2-6
447 #7
448 #1-4 6-8
Correction
Trial #2 [SO3] = 2.6x10^-4
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