Chapter 14
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Chapter 14. Equilibrium Suroviec Spring 2014. I. Equilibrium. So far we have mostly considered just forward reactions aA + bB  cC + dD. But all reactions can move in either direction. A. State of equilibrium. Rate of equilibrium. Equilibrium is dynamic. B. Positions of equilibrium.

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Chapter 14

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Chapter 14

Chapter 14

Equilibrium

Suroviec

Spring 2014


I equilibrium

I. Equilibrium

  • So far we have mostly considered just forward reactions

    aA + bB  cC + dD

  • But all reactions can move in either direction


A state of equilibrium

A. State of equilibrium

  • Rate of equilibrium

  • Equilibrium is dynamic


B positions of equilibrium

B. Positions of equilibrium


Ii equilibrium constant

II. Equilibrium Constant

  • Omit concentrations of pure solids and liquids because those concentrations will not change

  • Look at elementary steps:


A what does k mean

A. What does K mean?

  • Large value of K means product favored

2. Small value of K means reactant favored


Iii reaction quotient

III. Reaction Quotient


Example

Example

Given the K of this reaction to be 170, when the conditions are changed what is the Q?

Given the new Q, what is the direction of the reaction to re-establish equilibrium?


Iv calculations with k

IV. Calculations with K

  • We need the equilibrium concentrations to determine K, be we usually know initial concentrations, we can therefore get there from the balanced chemical equations!!!

  • Butane interconverts to isobutane at 25oC with a K = 2.5. If 0.017 moel of butane is in 50 mL, what is the concentration of both species at equilibrium?


Example1

Example

PCl5 (g) PCl3 (g) + Cl2 (g)

K is 1.2 at 25oC. If you place 0.300 M PCl5 (g) in a flask what are the equilibrium concentrations of PCl3 (g), PCl3 (g) and Cl2 (g)?


Example2

Example

H2 (g) + Br2(g)2HBr (g)

  • K is 2.18 × 106 at 730oC. If you place 0.267 M HBr (g) in a flask and allow it to come to equilibrium, what are the equilibrium concentrations of H2 (g), Br2 (g) and HBr (g)?


V manipulating equilibrium expressions

V. Manipulating Equilibrium Expressions

N2(g) + 3H2 (g) 2NH3 (g)

2N2(g) + 6H2 (g) 4NH3 (g)


Rules for manipulating

Rules for Manipulating

When the stoichiometric coefficients in a balanced reaction are changed by a factor of n:

  • When a chemical reaction is reversed in

  • direction:

  • When several balanced reactions (each with its own equilibrium constant) are added to obtain a net balanced equation:


Chapter 14

Ex

Calculation Knet for the following reaction:

Fe (s) + H2O (g) FeO (s) + H2 (g)

Given the following information:

H2O (g) + CO (g) H2 (g) + CO2 (g) K1 = 1.6

FeO (s) + CO (g) Fe (g) + CO2 (g) K2 = 0.67


Vi lechatelier s principle

VI. LeChatelier’s Principle

  • Any change in any of the factors that determine the equilibrium conditions of a system will cause the system to change in such a manner to counteract the effect of the change

  • Systems always want to be at equilibrium and will work to get back there.


Example3

Example

2SO2 (g) + O2 (g) 2SO3(g)ΔHrxn = -197 kJ

Disturbances:

  • Add more SO2(g)

  • Take away O2 (g)

  • Decrease the volume by ½


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