Georgia Performance Standards & Essential Questions:

1. SC2 Students will relate how the Law of Conservation of Matter is used to determine chemical composition in compounds and chemical reactions. f. Explain the role of equilibrium in chemical reactions. What causes chemical reactions to attain equilibrium? Georgia Performance Standards & Essential Questions:

2. Identify how equilibrium is established for various chemical reactions • Identify and discuss the characteristics of chemical equilibrium by applying the law of chemical equilibrium. • Calculate values for the equilibrium constant and for equilibrium concentrations. • Determine how the presence of solids or liquids affects the equilibrium expression • Predict the changes that occur when a system at equilibrium is disturbed • To learn to calculate equilibrium concentrations

3. The Concept of Equilibrium Chemical equilibrium occurs when a reaction and its reverse reaction proceed at the same rate.

4. Chemical Equilibrium • The state where the concentrations of all reactants and products remain constant with time. • On the molecular level, there is frantic activity.

5. D. The Equilibrium Condition • Equilibrium – the exact balancing of two processes, one of which is the opposite of the other

6. D. The Equilibrium Condition • Chemical equilibrium – a dynamic state where the concentrations of all reactants and products remain constant

7. Although time continues to pass, the numbers of reactant and product molecules are the same as in (c). No further changes are seen as time continues to pass. The system has reached equilibrium. The reaction continues as time passes and more reactants are changed to products. The reaction begins to occur, and some products (H2 and CO2) are formed. Equal numbers of moles of H2O and CO are mixed in a closed container. E. Chemical Equilibrium: A Dynamic Condition

8. E. Chemical Equilibrium: A Dynamic Condition • Why does equilibrium occur?

9. C. Heterogeneous Reactions • Homogeneous reaction – all reactants and products are in one phase • Gas • Solution • Heterogeneous reaction – reactants in two phases

10. B. Heterogeneous Equilibria • Heterogeneous equilibria – an equilibrium system where the products and reactants are not all in the same state

11. C. Heterogeneous Reactions

12. A. Le Chatelier’s Principle • Le Chatelier’s Principle – when a change is imposed on a system at equilibrium the position of the equilibrium shifts in a direction that tends to reduce the effect of that change

13. A. Le Chatelier’s Principle • Effect of a Change in Concentration

14. A. Le Chatelier’s Principle • Effect of a Change in Concentration • When a reactant or product is added the system shifts away from that added component. • If a reactant or product is removed, the system shifts toward the removed component.

15. The system is initially at equilibrium. The piston is pushed in, decreasing the volume and increasing the pressure. The system shifts in the direction that consumes CO2 molecules, lowering the pressure again. A. Le Chatelier’s Principle • Effect of a Change in Volume

16. A. Le Chatelier’s Principle • Effect of a Change in Volume • Decreasing the volume • The system shifts in the direction that gives the fewest number of gas molecules.

17. A. Le Chatelier’s Principle • Effect of a Change in Volume • Increasing the volume • The system shifts in the direction that increases its pressure.

18. A. Le Chatelier’s Principle • Effect of a Change in Temperature • The value of K changes with temperature. We can use this to predict the direction of this change. • Exothermic reaction – produces heat (heat is a product) • Adding energy shifts the equilibrium to the left (away from the heat term). • Endothermic reaction – absorbs energy (heat is a reactant) • Adding energy shifts the equilibrium to the right (away from the heat term).

19. Effects of Changes on the System • Concentration: The system will shift away from the added component. • Temperature: K will change depending upon the temperature (treat the energy change as a reactant). • Pressure: • Addition of inert gas does not affect the equilibrium position. • Decreasing the volume shifts the equilibrium toward the side with fewer moles.

20. LeChâtelier’s Principle

21. A. The Equilibrium Constant: An Introduction • Law of chemical equilibrium • For a reaction of the type • aA + bB cC + dD • Equilibrium expression • Each set of equilibrium concentrations is called an equilibrium position.

22. The Reaction Quotient (Q) • Q gives the same ratio the equilibrium expression gives, but for a system that is not at equilibrium. • To calculate Q, one substitutes the initial concentrations on reactants and products into the equilibrium expression.

23. If Q = K, then the system is at equilibrium.

24. If Q > K, then there is too much product, and the equilibrium shifts to the left.

25. If Q < K, then there is too much reactant, and the equilibrium shifts to the right.

26. B. Applications Involving the Equilibrium Constant • The Meaning of K • K > 1  the equilibrium position is far to the right • K < 1  the equilibrium position is far to the left

27. B. Applications Involving the Equilibrium Constant • The value of K for a system can be calculated from a known set of equilibrium concentrations. • Unknown equilibrium concentrations can be calculated if the value of K and the remaining equilibrium concentrations are known.