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Chemical Equilibrium

For use with Holt Chemistry, Chapter 14

Eowyn Johnson

on 2 February 2012

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Transcript of Chemical Equilibrium

CHEMICAL EQUILIBRIUM Reversible Reactions and Equilibrium Systems at Equilibrium Equilibrium Systems and Stress Vocabulary Examples of Equilibria Reversible reaction--products reform the original reactants
Common example are sunglasses containing light sensitive silver chloride
Chemical equilibrium--rate of a forward reaction equals the rate of the reverse reaction
In chemical equilibrium the concentrations of the products and reactants remain unchanged Studying Reactions at Equilibrium Complex Ions Complex ions are metal ions at the center with additional molecules or ions surrounding that metal ion
Ligands are the molecules or ions surrounding the central ion. Metal ions in a body of water are surrounded by water molecules. When a stronger ligand is introduced, the new ligand may replace the water. Calculating Keq
Keq relates the concentrations of reactants to products at a given temperature
Keq = [products]/[reactants]
Keq > 1 higher product concentration (favorable)
Keq = 1 reactant and product concentrations equal
Keq < 1 higher reactant product concentrations (unfavorable) Using Keq
Caves form where large amounts of limestone (CaCO3)
Rainwater contains dissolved CO2 and can dissolve limestone (see page 502)
When solution reaches roof of cave, cave often has less [CO2] than outside air and solution loses CO2 when drips from ceiling
Loss causes shift left and causes CaCO3 to ppt--forms stalagtites and stalagmites
Calculating Ksp
Ksp is the equilibrium constant for a solid that is in equilibrium with the solid's dissolved ions
Calculated for slightly soluble salts
Ksp = [cations][anions}

Practicing Calculating Ksp 1. Calculate the solubility product constant of HgI2 if the Hg2+ concentration in a saturated solution is 1.9 x 10-10. 2. Calculate the solubility product constant of Fe(OH)2 if the OH- concentration in a saturated solution is 4.6 x 10-6. 2. The Ksp of CdF2 is 6.4 x 10-3 Calculate the concentration of the ions in a saturated solution of CdF2. Ksp = 2.7 x 10-29 Ksp = 4.9 x 10-17 Ksp = [Cd2+] = 0.12; [F-] = 0.24 Importance of Ksp
Some compounds are useful because they are quite soluble
Others are more useful because they are only slightly soluble
LeChatelier's Principle
When a system in equilibrium is disturbed, the system will adjust to a new equilibrium
The system will oppose the change in away that helps eliminate the change Causes of Change (Stresses)
Change in concentration--increase will shift away from higher concentration
Temperature--increasing the temperature causes the reaction to shift to the endothermic reaction
Temperature--decreasing the temperature causes the reaction to shift to the exothermic reaction
Pressure (only affects gases)--increasing the pressures causes a shift to the side with fewer gas molecules Examples of LeChatelier's Principle Predict the shift. Choose which reaction will be favored (forward, reverse, or neither) Do page 522, # 19. a. forward e. reverse
b. forward f. neither
c. neither g. reverse
d. forward h. neither Now try #20. a. high reactant concentrations, high pressure, and low temperature
b. high reactant concentrations, low temperature,
c. high reactant concentrations, high temperature
d. high reactant concentrations, high pressure, low temperature The equilibrium constant is a specific ratio of the products to the reactants. The common ion effect
• Based upon Le Chatelier's Principle, if we
add an ion common to the solid, to the
medium or solution, the equilibrium will shift to make the solid less soluble. Be able to…
- state Le Chatelier’s principle
- apply the principle to predict if forward or reverse reaction is favored under certain stresses. Warm up:
1.Make a list of examples of everyday adjustments that are made to relieve stress on a system… (include at least 5)

ex. its cold outside so you put on a coat.
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