# Chapter 14 - PowerPoint PPT Presentation

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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

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

### 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?

• Large value of K means product favored

2. Small value of K means reactant favored

### 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

• 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?

### 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)?

### 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

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

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

### 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:

### 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

• 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.

### Example

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

Disturbances: