Section 17-2

1. Section 17.2 Factors Affecting Chemical Equilibrium • Describe how various factors affect chemical equilibrium. • Explain how Le Châtelier’s principle applies to equilibrium systems. When changes are made to a system at equilibrium, the system shifts to a new equilibrium position. Section 17-2

2. Le Châtelier’s Principle • Le Châtelier’s Principle was proposed in 1888 and states that if stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress. • Stress is any kind of change in a system that upsets the equilibrium. Section 17-2

3. Le Châtelier’s Principle (cont.) • Adjusting the concentrations of either the reactants or the products puts stress on a system in equilibrium. • Adding reactants increases the number of effective collisions between molecules and upsets the equilibrium. Section 17-2

4. Le Châtelier’s Principle (cont.) • The equilibrium shifts to the right to produce more products. • Stress is relieved by shifting to the left, converting products to reactants. Section 17-2

5. What dose the longer equilibrium arrow to the left or right mean? • It means that, one reaction occurs faster than the other temporarily. Once a new equilibrium position is established, the two reactions again occur at equal rates

6. Le Châtelier’s Principle (cont.) • Changing the volume (and pressure) of an equilibrium system shifts the equilibrium only if the number of moles of gaseous reactants is different from the moles of gaseous products. • CO(g)+ 3H2(g)⇌ CH4(g)+ H2O(g) • If the number of moles is the same on both sides of the balanced equation, changes in pressure and volume have no effect on the equilibrium. Section 17-2

7. Le Châtelier’s Principle (cont.) The reaction between CO and H2 is at equilibrium. Lowering the piston decreases the volume and increases the pressure. As a result, more molecules of the products form. Their formation relieves the stress on the system. Section 17-2

8. Le Châtelier’s Principle (cont.) • Changes in temperature alter the equilibrium position and the equilibrium constant. • If heat is added to an equilibrium system, the equilibrium shifts in the direction in which the heat is used up. Section 17-2

9. Le Châtelier’s Principle (cont.) • Any change in temperature results in a change in Keq. Section 17-2

10. Le Châtelier’s Principle (cont.) • A catalyzed reaction reaches equilibrium more quickly, but with no change in the amount of product formed. Section 17-2

11. A B C D Section 17.2 Assessment Which does NOT result in a shift of the equilibrium to the right? A.removing products B.adding reactants C.increasing concentration of reactants D.adding products Section 17-2

12. A B C D Section 17.2 Assessment Any change in ____ results in a change in Keq. A.temperature B.pressure C.volume D.concentration Section 17-2

13. A B C D A change in ____ alters both the equilibrium position and the equilibrium constant. A.pressure B.temperature C.volume D.density Chapter Assessment 1

14. A B C D Adding product to a chemical equilibrium: A.does nothing B.creates a stress and shifts the equilibrium to the right C.creates a stress and shifts the equilibrium to the left D.causes more product to form STP 3

15. A B C D Ethylene (C2H4) reacts with hydrogen to form ethane (C2H6). C2H4(g) + H2(g) ↔ C2H6(g) + heat. How could you increase the amount of hydrogen in the system? A.Increase the heat. B.Decrease the heat. C.Increase the C2H4. D.Decrease the C2H6. STP 4

16. A B C D Which does NOT result in a shift of the equilibrium to the right? A.removing products B.adding reactants C.increasing concentration of reactants D.decreasing the concentration of reactants STP 5

17. Q1:why the addition of a catalyst does not change an equilibrium position. • A catalyst speeds up the forward and reverse reactions equally. • Q2: Explain how the following stresses affect the equilibrium system. • PF3(g) + F2(g) ⇌ PF5(g) + heat • If volume is decreased: The equilibrium shifts to the right. • Heat is increased : The equilibrium shifts to the left.

18. Q3:Explain how a system at equilibrium responds to a stress and list factors that can be stresses on an equilibrium system. • If possible, the equilibrium shifts in the direction that relieves the stress. changes in concentration, pressure (volume), and temperature

19. Q4:Explain how decreasing the volume of the reaction vessel affects each equilibrium. • 2SO(g) + O2(g) ⇌ 2SO(g) • H2 (g) + Cl2(g) ⇌ 2HCl(g) a. The equilibrium shifts to the right. b.The stress has no effect on the equilibrium

20. Q5: Decide whether higher or lower temperatures will produce more CH3CHO in the following equilibrium. C2H2(g) + H2O(g) ⇌ CH3CHO(g) ∆H° = -151 kJ lower temperatures

21. Q6: The table below shows the concentrations of Substances A and B in two reaction mixtures. A and B react according to the equation 2A ⇌ B; K eq = 200. Are the two mixtures at different equilibrium positions? The two mixtures are at the same equilibrium position.

22. End of section 17.2