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UTMB / Chemistry / CHEM 302 / What is an equilibrium constant?

What is an equilibrium constant?

What is an equilibrium constant?

Description

School: The University of Texas Medical Branch
Department: Chemistry
Course: Principles of Chemistry II
Professor: Kate biberdorf
Term: Spring 2017
Tags: General Chemistry and Chemistry
Cost: 25
Name: Chem 302 LEs 11-14
Description: These notes cover the material presented in LES 11-14
Uploaded: 02/17/2017
6 Pages 40 Views 1 Unlocks
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LE 11: EQUILIBRIUM CONSTANTSIf you want to learn more check out What is virtual infrastructure?

We also discuss several other topics like What rock is igneous rock?

Equilibrium ConstantIf you want to learn more check out What are the different types of unemployment?

  • When a system in equilibrium G = 0, no net changes in pressure or concentrations
  • Specific value for mass action expression = equilibrium constant
  • Found by plugging equilibrium values into mass action expression

Don't forget about the age old question of Was the modern revolution positive or negative?

Reaction: aA + bB ⇌ cC + dDIf you want to learn more check out What is global max/min?

         where “𝛂” is the activity; “K” = is the equilibrium constant and the “goal” of the reaction

  • The activities for liquids and solids always one (gas and aqueous have values)

If you want to learn more check out Define the idea of humanism.

Ex) C2CO3(s) ⇌ C2O(s) + CO2(g)

  • ; Kp for partial pressures (i.e. gas)
  • Number of mols becomes exponent 4H2 -> [H2]4
  • Kc ; Kc used to denote concentrations
  • If K is larger than 1 reaction favors products and higher concentrations of products exist at equilibrium.
  • If K is less than 1, reaction favors reactants

Manipulating K

  • For reverse reaction, Kreverse =
  • For doubled reaction (2A + 2B -> 2C)
  • K2 = K2
  • For two reactions:
  • A + B ⇌ C (K1);  C ⇌ D (K2)
  •  A + B ⇌ D; K1 ● K2 = K
  • Kp for partial pressures of gas
  • Kc for concentrations in moles
  • Kp = Kc(RT)Δn
  • R = .08206
  • where Δn is the change in the number of moles of gas (products - reactants)
  • if Δn = 0 then Kp = Kc

LE 12: FREE ENERGY AND EQUILIBRIUM

ΔG and Equilibria

  • Systems go into equilibrium because it is a place of lowest energy
  • Depends on compounds as well as concentrations
  • ΔGr = ΔGor + RT ln(Q)
  • Instantaneous difference in free energy between reactants and products at any given set of concentrations
  • ΔGor is the calculated difference in free energy of pure products and pure reactants
  • ΔGor < 0 , products have lower G
  • ΔGor > 0 , reactants have lowe G
  • Q < K
  • Lowest point of Gibbs free energy (favors products)
  • Always somewhere in between because mixing increases entropy
  • Q > K
  • Reverse reaction, favors reactants
  • At equilibrium, ΔGr = 0, thus Q = K and ΔGro = -RT lnK
  • *use R = 8.314
  • If ΔGro < 0 , K > 1 , favors products
  • If ΔGro > 0 , K < 1 , favors reactants
  • If ΔGro = 0 , K = 0
  • If Q > K reaction will favor reactants
  • If Q < K reaction will favor products

LE 13: RICE TABLES

  • Rice tables used to find pressures and concentrations needed for a system to be in equilibrium that is out of equilibrium (where Q ≠ K)
  • Reaction itself
  • Initial conditions of concentration or pressure
  • Change line - amount that reacts
  • Equilibrium - amount that is written out

  • Solve for x the unknown amount that reacts

Ex) A + B ⇌ 2C

        Given: K = 4, A = .1 m, B = .1 m, C = 0

        Q is 0, therefore forward reaction

R                A        +        B        ⇌        C

I                .1                .1                0

C                -x                -x                +2x

E                .1 - x                .1 - x                2x

stoichiometry

K = ; solve for x; x = 0.05

        Now A = .05 m, B = .05 m, and C = .1m

LE 13: LE CHATELIER’S PRINCIPLE

  • If a chemical system at equilibrium undergoes a change, the equilibrium will shift to counteract the change and a new equilibrium is established.
  • Want Q = K
  • If Q becomes greater than K, reaction goes left
  • If Q becomes less than K, reaction goes right

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