B. How does equilibrium respond to stress? Stress = causes a change in a system at equilibrium such as a change in,. or. Ms.

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Camilla Fitzgerald
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concentrations of products and reactants remain.

of product until equilibrium is reached.

1 Equilibrium Notes (Ch. 14) A. Equilibrium -is a state of -the rate of a reaction = the rate of the reaction concentrations of products and reactants remain. The concentration of reactant, N 2 O 4, because N 2 O is formed & the conc. of product until equilibrium is reached. The rate of forward reaction is equal to the rate of reverse reaction when equilibrium is reached. B. How does equilibrium respond to stress? Stress = causes a change in a system at equilibrium such as a change in,. or. Ms. Park Page 1

but the system soon reaches a new equilibrium.

2 C. What is Le Chatelier s Principle? When a is applied to a system, at first, equilibrium is disturbed and the rates of the forward and backward reactions are equal, but the system soon reaches a new equilibrium. In order to maintain equilibrium (or homeostasis), in a reaction, a reaction shifts in a direction from the side w/ or concentration to the side w/ or concentration. Ex. N2O4 (g) <-> 2 NO2 (g) (.) D. See Saw Model Equilibrium Increase in concentration of A Shift to to achieve equilibrium by Ms. Park Page 2

3 E. Equilibrium in Human Body resists the change in ph The following is the system. CO 2 + H 2 O <-> H 2 CO 3 ( acid) H 2 CO 3 <-> H + + HCO 3 - When an acid (H+) is added, it shifts to the. When a base (OH-) is added or H+ is removed, it shifts to the. If [H+] stays constant, the ph stays the same. F. Factors that affect equilibrium 1. CONCENTRATION affects the side with higher conc. [ ] to [ ] 2. TEMPERATURE affects the side with energy on it. High temp from the energy side Low temp the energy side 3. PRESSURE affects entropy (or ). High pressure toward disorder (ex. less # of molecules) Low pressure toward disorder (ex. more # of molecules) G. Change in Concentration When [NO 2 ] increases, the equilibrium shifts to the. When [NO 2 ] decreases, the equilibrium shifts to the. When [N 2 O 4 ] inc., the equilibrium shifts to the. When [N 2 O 4 ] dec., the equilibrium shifts to the. H. Changes in Temp. This reaction is an reaction. If temp is increased the rxn. will shift to the. If it shifts to the, the conc. of all reactants will increase and all products will decrease. I. Changes in Pressure Ms. Park Page 3

4 If pressure is, the rxn. will shift to the b/c the side has molecules/pressure. Count the total # of on each side. (Less # of molecules mean.) ***Ignore solid and liquid. No equil. shift. b/c only gases are or change due to pressure. J. Predict the shift (left or right) when these changes occur. Examples: N2 (g) + 3 H2 (g) 2 NH3(g) + heat Temperature is decreased. Pressure is decreased. [H2] is increased. [NH3] is increased. Learning Check 1. P4 (s) + 6 Cl2(g) -> 4 PCl3 (l) a. When P4 is added, which way the rxn will shift? b. What happens to [Cl 2 ], and [PCl 3 ]? c. When PCl3 is added, which way the rxn will shift? d. When PCl3 is added, what happens to conc. of each reactant? 2. Heat + NH 4 Cl (s) <-> NH 3 (g) + HCl (g) a. When temp. increases, the rxn shifts to the. b. When temp. decreases, the rxn shifts to the. K. Equilibrium Constant Expression Keq = [product]/[reactant] [ ] means concentration. Equilibrium constant (Keq) = constant number that relates the concentration of reactants & products. - become the. ****Exclude pure solid and liquid. Include only and substances wa + xb <===> yc + zd Keq = [C] y [D] z [A] w [B] x Ms. Park Page 4

5 L. Equilibrium Constant Expression Example N 2 (g) + 3 H 2 (g) <-> 2 NH 3 (g) Keq = [NH 3 ] 2 [N2] [H2] 3 The coefficients become exponents. M. Equilibrium Constant Expression Example (with numbers) 2 HI(g) H2 (g)+ I2 (g) What is the Keq? The equilibrium conc. are : [HI] = M [H2] = M [I2] = M Ms. Park Page 5

Chemical Equilibrium

Chemical Equilibrium What is equilibrium? Expressions for equilibrium constants, K eq ; Calculating K eq using equilibrium concentrations; Factors that affect equilibrium; Le Chatelier s Principle What