CHEMICAL EQUILIBRIUM

REVIEW

REVIEWLook at the review objectives and your notes.1. Describe a reversible reaction.Be sure you can describe what a reversible reaction is, how

it is designated (↔), and whether or not all reactions are reversible.

2. Describe the state of dynamic chemical equilibrium and explain how it is achieved.

What is chemical equilibrium, how is it maintained and what is present at equilibrium.

3. Write the equilibrium rate expression for any system at equilibrium.Just like the quiz, #1.

REVIEW

4. Calculate Keq given the concentrations of products and reactants at equilibrium.

Just like the quiz, #2.5. Given Keq, calculate the equilibrium concentrations of

products and reactants at equilibrium. Just like the quiz, #3.6. Calculate the reaction quotient, Q, and relate it to Keq.

Determine in which direction the reaction will proceed (shift left, shift right, at equilibrium).

Just like the quiz, #4.

REVIEW7. Describe Le Chatelier’s Principle and the stresses that

can alter equilibrium (concentration, pressure, and temperature).

be sure you can define it and list the stresses that can alter equilibrium.

8. Use Le Chatelier’s Principle to predict shift in equilibrium in terms of relative concentrations of products and reactants. Understand what changes in temperature, pressure (volume), concentration, and moles (pressure) can do.

Be sure you can do problems like the grid, study guide, and sheet given today to practice on.

LECHATELIERS PRINCIPLE SUMMARY

ConcentrationWhat ever you add will be used up as the reaction tries to return to equilibrium.• Add more reactant, rxn proceeds right• Add more product, rxn proceeds left• Remove reactant, rxn proceeds left• Remove product, rxn proceeds right

LECHATELIERS PRINCIPLE SUMMARY

PressureWhen dealing with gases, you must number the amount of moles on each side of the equation.• if you increase the pressure, the equilibrium will shift so that

there will be fewer moles of gas.• Increase pressure, shifts to fewer moles. If both sides have

the same number of moles, there is no effect.• Decrease pressure and the side with more moles is favored.

LECHATELIERS PRINCIPLE SUMMARY

TemperatureYou must know if the reaction is exothermic or endothermic.• If heat is on the reactant side of the reaction:• Add heat, shifts to the product.• Take away heat, shifts to the reactant

• If heat is on the product side of the reaction:• Add heat, shifts to the reactant.• Take away heat, shifts to the product.

LECHATELIERS PRINCIPLE SUMMARY

Catalyst• Adding a catalyst changes the rate, not the equilibrium.  REMEMBER:**Changing the concentration or the pressure does not affect Keq, but will affect the equilibrium position. Only changing the temperature will affect Keq.

REVIEW

9. Describe the significance of the size of Keq in an equilibrium system.

Remember that if Keq < one, there are more reactants at EQ. If Keq > one, there are more products at EQ.

TEST FORMAT

•Multiple Choice, 10-16• Problems just like the quiz, 1-2 each• Problems formatted just like LeChatelier’s

Principle handouts

MORE INFORMATION• This powerpoint, minus the handout answers, is on the web

under today’s date on the Pitts’ Chemical Classes page.• If you are not very good at multiple choice questions, there

are some at the back of each chapter (pages 630-631 for chapter 17).• The answers to the two review sheets (LeChatelier’s Principle

and Chemical Equilibrium Problem Set are available to look at in room 2404 this Friday after school or Monday before school. The purpose of releasing the answers is for you to TRY the problems first and check your work – NOT to copy the answers.