Equilibrium

1. Equilibrium

2. Introduction • up until now, equations that we have looked at have always had an arrow going in one direction • NaCl --> Na+ + Cl- • this idea has been an example of oversimplification(at best) and an outright lie(at worst)

3. Introduction • actually, most reactions are said to be in equilibrium, which means that it tends to move back and forth and not only in one direction • there are four possibilities when talking about any reaction

4. 1. the reaction moves only in one direction 2H2 + O2 --> 2HOH 2. the reaction moves mostly to the right with a little bit of it going back NaCl -----> <-- Na+ + Cl-

5. 3. the reaction moves mostly to the left with a little bit of it going right PbCl2 --> <--------- Pb+2 + 2 Cl- 4. the reaction is in perfect equilibrium NaC2H3O2 ----> <---- Na+ + C2H3O2-

6. Equilibrium Constant • arrows are all well and good but are less than satisfying in explaining to us the extent to which a reaction will occur, we need more tangible, more quantitative evidence • equilibrium constant(K) gives us a good way of determining how product favored(arrow to the right) or reactant favored(arrow to the left)

7. Equilibrium Constant • Equilibrium constant is measured by using the concentrations of the reactants and product at Equilibrium and the balanced equation

8. Equilibrium Constant General Equation: aA + bB <--> cC +dD K = [C]cx [D]d [A]a x [B]b [C] = product concentration of ion or gas C [D] = product concentration of ion or gas D [A] = reactant concentration of ion or gas A [B] = reactant concentration of ion or gas B

9. Equilibrium Constant c= coefficient of gas or ion C taken from balanced equation d= coefficient of gas or ion D taken from balanced equation a= coefficient of gas or ion A taken from balanced equation b= coefficient of gas or ion B taken from balanced equation

10. Equilibrium Constant • K will not have any units associated with it, it is just a number • if K is greater than 1, it means that you will have more products than reactant at equilibrium so it is Product favored(arrow leaning toward product side)

11. Equilibrium Constant • if K is 1 than it is in perfect equilibrium, no tendency to go to left or right(arrows equal) • if K is less than 1, it means that you will have more reactants than products at equilibrium so it is reactant favored(arrow leaning toward reactant side)

12. Equilibrium Constant • VIF: since only gases and ions can be measured in M, liquids and solids are not included in Equilibrium equations: leave them out!!

13. Equilibrium Constant Ex.1 At a given temperature:: 2HI(g) <--> H2(g) + I2(g) a. set up the equilibrium equation b. what is value of K for the reaction if the equilibrium concentrations are: [HI] = 1.69 x 10-3M, [H2] and [I2] are both 2 x 10-4 M c. is this equation product favored or reactant favored, or both?

14. Equilibrium Constant Ex. 2 At a given temperature, the reaction: CO(g)+ HOH(g) <--> H2(g) + CO2(g) with the following concentrations: [CO] = .2M, [HOH] = .5 M, [H2] = 0.32 M, [CO2] = .42 M a. set up the equilibrium equation b. what is value of K c. is this equation product favored or reactant favored, or both?

15. Equilibrium Constant Ex. 3 At a given temperature, the reaction: CaCO3(s) --> CO2(g) + CaO(s), with the following concentration: [CO2] = .50 M a. set up the equilibrium equation b. what is value of K c. is this equation product favored or reactant favored, or both?

16. Le Chatelier’s Principle • notice that the above examples were always at a given temperature, that is because Equilibrium can be changed by changing the temperature • if a system is in equilibrium, changing the concentration of any of the reactants or products, changing the Temperature, or changing the Pressure can alter the equilibrium and make the equation swing in one direction or another in order to undo the damage

17. Le Chatelier’s Principle • Le Chatelier’s Principle states that if a change is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction that tends to reduce the change

18. Three Possibilities 1. Change in concentration: • if you increase the concentration of a reactant, the reaction will move toward the right to get rid of the extra reactant • if you decrease the concentration of a reactant, the reaction will move toward the left to make up for the loss

19. Three Possibilities • same for products Ex. 4 Predict in which direction the equilibrium will shift for the reaction: As4O6(s) + 6C(s) <--> As4(g) + 6 CO(g) with: a. an addition of carbon monoxide b. an addition or removal of carbon or As4O6 c. removal of As4

20. 2. Changes in Temperature 2. Change in Temperature • treat Energy like as if it were a reactant or product • if the reaction is exothermic and you add energy: the reaction shifts to the left in order to use up the the extra energy

21. 2. Changes in Temperature • if the reaction is exothermic and you take away energy(lowering T), the reaction shifts to the right in order to make up for the loss of energy • same for an endothermic reaction • ∆H and q are the same thing

22. 2. Changes in Temperature • a negative ∆H means exothermic: “energy” is a product • a positive ∆H means endothermic: “energy” is a reactant

23. 2. Changes in Temperature Ex. 5 Predict in which direction the equilibrium will shift for the reaction: N2(g) + O2(g) <--> 2NO(g) ∆H(q)= 181 KJ with an increase of Temperature Ex. 6 Predict in which direction the equilibrium will shift for the reaction: 2SO2(g) + O2(g) <--> 2SO3(g) ∆H(q)= -198 KJ with an increase of Temperature

24. 3. Changes in Pressure • an increase in Pressure will cause the reaction to move toward the side that is most compact, the side that has the least number of moles of gases • a decrease in Pressure will cause the reaction to move toward the side that has the most number of moles of gas

25. 3. Changes in Pressure • Ex. 7 Predict the shift in equilibrium position that will occur for each of the following processes when the volume is reduced: a. P4(s) + 6Cl2(g) <--> 4PCl3(l) b. PCl3(g) + Cl2(g) <--> PCl5(g) c. PCl3(g) + 3NH3(g) <--> P(NH2)3 (g) + 3HCl(g)

26. Ksp • remember several months ago, I lied to you about there being ionic compounds that do not dissolve • well, ALL IONIC COMPOUNDS DISSOLVE • actually, some of them dissolve to such a tiny extent, that we simply cannot see them dissolving so we say that they are insoluble(for all practical purposes)

27. Ksp • what happens is that they reach equilibrium really quickly… • Ex. 1 AgCl <--> Ag+(aq) and Cl-(aq) • very little of the AgCl actually breaks down • if we were to wait a few minutes and test for Ag+ and Cl- we would find that their concentration was 1.3 x 10-5 M

28. Ksp • so using our rules for Equilibrium we would first set up the equation like this: • K = [Ag+] x [Cl-] -remember that AgCl is a solid so it would not be found in the expression • in order to find K we would then plug in the concentrations • K = [1.3 x 10-5 M] x [1.3 x 10-5 M]

29. Ksp • K = 1.7 x 10-10–definitely a reactant favored reaction • there are many types of Equilibrium expression • Ka = refers to the equilibrium established by a weak acid, the smaller the equilibrium(the bigger the exponent), the weaker the acid • Kb = refers to the equilibrium established by a weak base, the smaller the equilibrium(the bigger the exponent), the weaker the base

30. Ksp • Ksp = refers to solubility product constant and it is the K that you will see associated with this concept • there are two kinds of questions that you will see associated with this concept

31. Ex. 1 What is the solubility, in moles per Liter, of BaF2, if the Ksp is 1.7 x 10-6? Step number one: Write an equation for the dissolving of BaF2 BaF2(s) <--> Ba+2(aq) + 2F-(aq) --realize that • for every one BaF2 that dissolve you make 3 ions(1 Ba+2and 2 F-) Step number two: Write the equilibrium expression: Ksp = [Ba+2] x [F-]2

32. Step number three: You are trying to find the amount of BaF2 that dissolves, BaF2 is not part of the equation, but, since for every BaF2 that dissolves you get one Ba+2, if you find Ba+2, you find BaF2, so: • Set Ba+2= x and F- = 2x(since you get 2 F- for the price of one Ba+2 • Ksp = 1.7 x 10-6 = [x] * [2x]2 • Step number four: Solve for x

33. Ex. 2 If the solubility of Cd(OH)2 is 1.7 x 10-5M, what is its Ksp? Step number one: Write an equation for the dissolving of Cd(OH)2 Cd(OH)2 <--> Cd+2+ 2OH- Step number two: Write the equilibrium expression: Ksp = [Cd+2] x [OH-]2

34. Step number three: You already know how many Cd(OH)2’s dissolved(1.7 x 10-5), since you know that for every one of these that dissolves you get 1 Cd+2 and 2 OH-, then you have Cd+2=1.7 x 10-5 and OH- = 2(1.7 x 10-5) Ksp = [1.7 x 10-5] [2(1.7 x 10-5)]2

35. Entropy • Study of Chemistry has yielded a good understanding of what Mother Nature likes and does not like • Two things that we have realized that seems to make Mother Nature happy are: a. Mother Nature likes to spread out energy so Mom prefers exothermic reactions(negative H(enthalpy) b. Mother Nature likes to make simpler molecules out of more complex ones

36. Entropy • Entropy is the study of this tendency, it is the tendency of Mother Nature to take very orderly • substances such as solids and liquids and convert them into gases • We say that Nature by and large is increasing in disorder(Entropy)

37. Entropy • you do not believe me? What happens to your locker over the course of the school year? What happens to your bedroom within days of you cleaning it? What has happened to human beings over the course of thousands of years(most of us can’t even use our wisdom teeth for goodness sakes) • everything tend to go toward decay, disorder!

38. Entropy • But you might say: if I constantly keep up with my room, it does not degenerate into a mess! • Yes, but you have to use energy to do so! Mother Nature will allow you to slow down the rate of decay if you are willing to spread out the energy(look at Number One above) Symbol for Entropy is S • If a reaction increases in disorder we say that the ∆S is positive • If a reaction becomes more orderly we say that the ∆S is negative

39. Entropy • If the ∆S is positive, we say that the reaction is likely to occur and therefore spontaneous • If the ∆S is negative, we say that the reaction is not likely to occur and therefore nonspontaneous

40. Entropy • Questions concerning Entropy are really easy to answer • I am going to give you an equation with phases on each reactant and product • You need to look and see if the reaction is becoming more disorderly, solids are more orderly than liquids, liquids are more orderly than gases, solids are more orderly than dissolved ions

41. Entropy • if the reaction is more disorderly, we say that entropy has increased • if the reaction is more orderly, we say that entropy has decreased Ex. Determine whether the following reactions show an increase or a decrease in entropy 1. CO2(s) --> CO2(g) 2. H2O(s) --> H2O(l)

42. 3. KCl(s) --> K+(aq) + Cl-(aq) 4. H2(g) + 2O2(g) --> HOH(g) 5. 2Na(s) + I2(s) --> 2NaI(s) 6. Na+(aq) + Cl-(aq) --> NaCl(s) 7. Na2O(s) + HOH(l) --> 2Na+(aq) + 2OH-(aq) 8. SO3(g) + H2O(l) --> H+(aq) + HSO4-(aq)

43. Nuclear Chemistry • up until now, all the reactions we have looked have been either chemical or physical reactions. • as far as chemical reactions are concerned, the reaction only takes place between the outer shell of atoms • the nucleus and the kernal electrons have nothing to do

44. Nuclear Chemistry • but in nuclear reactions, it is in the nucleus that most of the action takes place • remember that the nucleus is a bunch of protons and neutrons held together by the Strong Force(if you are a wave physicist) or gluons(if you are a particle physicist) • Strong Force(or gluons) must be very strong in order to hold a bunch of positive particles together

45. Nuclear Chemistry • but life in the nucleus is a very tenuous thing, and every so often, the particles will overcome the Strong force and break apart-this is called a nuclear reaction • nobody really knows for sure why some isotopes never break up(stable) and why some have a tendency to break up(unstable)

46. Nuclear Chemistry • when atoms break apart they usually break up into 1 or more smaller parts called daughter nuclei • atoms that are unstable are called radioisotope • along with the daughter nuclei, small bits and pieces of the nucleus and/or Energy may be released when the atoms blow up, this is called radiation or radioactive particles

47. Nuclear Chemistry • there are various kinds of radiation, the five most popular are: 1. alpha particle-in essence, it is a clump of nucleus containing 2 protons and 2 neutrons, because it is basically the same thing as the He nucleus, its nuclear symbol is 42He, its Greek symbol is • Ex. 23090 Th --> 4 2 He + 22688 Ra

48. Nuclear Chemistry 2. Beta particle-tiny negatively charged particle, it comes into existence when a neutron breaks apart from a proton and a beta particle, so the mass number would not change but the number of protons would go up by one, its nuclear symbol is 0–1 e-, its Greek symbol is ß • Ex. 22688 Ra --> 22689 Ac + 0–1 e-

49. Nuclear Chemistry 3. Gamma radiation-unlike the previous two types, this is just pure radiation. Physicists believe that since you get a smaller nuclei in this reaction, the nuclei does not need as much of the Strong Force anymore so the excess is given off. It does not have a nuclear symbol because it has no mass, it is not made of matter, its Greek symbol is

50. Nuclear Chemistry 4. Neutron-just what the name implies, given the symbol 10 n • 10 n + 23592 U --> 14156 Ba + 9236 K + 3 10 n • 5. Positron-the alter ego of the Beta particle, it is the anti beta, 01 e • 147 N --> 01 e + 146 C