Download 1 Unit 11-12: Equilibrium and Acid/Bases Notes Colligative

Name: _________KEY_________ Block: ____________ Unit 11‐12: Equilibrium and Acid/Bases Notes Colligative Properties Notes
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Colligative properties‐ property that depends on the concentration of solute particles, not their identity Freezing point depression (Δtf)‐ freezing point of a solution is lower than the freezing point of the pure solvent Boiling point elevation (Δtb)‐ boiling point of a solution is higher than the boiling point of the pure solvent Calculating Changes in Freezing or Boiling Points
Boiling Point Elevation: ΔTb = imkb
Freezing Point Depression: ΔTf = imkf
ΔTb or ΔTf = change in the solvent’s boiling point or freezing point
i= the number of solute particles (ions that disassociate)
m= molality (moles solute/kg solvent)
kb or kf = constant for the bp or fp for a solvent (factor for how much the bp or
fp can change)
Example: If 45.0 g of glucose are dissolved in 255 g of water what will the boiling point and freezing
point of the solution be of the solution? The kb of water is 0.515 oC/m; the kf of water is 1.86 oC/m.
Boiling Point ΔTb = imkb
i = glucose (does not disassociate) so it is 1 m = moles 45 g glucose 1 mole = 0.25 moles
Kg
180g C6H12O6
m = 0.25 moles = 098 m
kb = 0.515 ºC/m
ΔTb = imkb (1) (0.98 m) (0.515 ºC/m) = .505 ºC
so 100 ºC + 0.505 ºC = 100.505 ºC elevation
0.225 kg
Freezing Point: ΔTf = imkf kf = 1.86 ºC/m
ΔTb = imkf (1) (0.98 m) (1.86 ºC/m) = 1.82 ºC
so 0 ºC - 1.82 ºC = - 1.82 ºC depression
1 Reaction Rate: To make a reaction go faster:  Increase temperature ‐ a direct relationship between kinetic energy and temperature exists ‐ the higher the temp, the faster the molecules will go ‐ more chaotic motion will lead to more collisions  Increase surface area of reactants ‐ the more sites exposed to react, the more collisions can occur ‐ a large piece of copper will react slower in acid than many small pieces  Increase concentration of reactants ‐ more moles (therefore particles) available to react in a 6.0M solution vs. a 0.10M solution ‐ copper will react faster with 6.0 M acid than 0.10 M. 
Add a catalyst ‐ will speed up the reaction by lowering activation energy, Ea ‐ pathway with added catalyst.... with Catalyst Why do reactions occur at different rates? Conditions are different for each reaction for example: it could take several steps, the molecular shape, and the state (phase) or size of the reactants What prevents a reaction from occurring immediately? The energy is too low or something inhibits molecules from colliding. Why don’t all products form at the same instant? It requires molecules to collide in proper alignments * Each reaction is special. Conditions are different for each reaction. Sometimes it takes longer for molecules/atoms to arrange themselves so they can react, therefore forming new substances 2 Chemical Equilibrium  A state when the concentrations of all substances in a reaction remain constant  You have assumed that when reactants  products, the only “thing” in a reaction vessel (beaker) are the products and excess reactants  In other words, you have assumed that all reactions proceed to completion  However, most reaction are actually REVERSIBLE ex: H2O (g) + CO (g)  H2 (g) + CO2 (g)  The “reverse arrow” indicates that the reaction can occur in either direction until equilibrium occurs (The amount of Products do not have to equal Reactants, but the rate they are produced are equal).  No net changes occur that are visible at equilibrium, but on the molecular level, reaction still occurs  No changes in concentration occurs once equilibrium has been established Graph: Concentration vs Time  water and carbon monoxide decrease over time, they’re the reactants, they go away  hydrogen and carbon dioxide are the products, there is no concentration of them initially, because they have not yet been formed, they increase over time  The Reaction is said to be AT EQUILIBRIUM when Rate forward Reaction= Rate Reverse Reaction ‐ With kinetics, we saw that the rate of the forward reaction slows (neg sign) because the reactants are being used up, the opposite applies for the reverse reaction ‐ Once some of the products form, they can react together to form “reactants.” Their rate of reaction starts slow (rate reverse), but increases ‐ When the rates equal, equilibrium has been achieved. 3 The Equilibrium Constant, K or Kc or Keq The constant, K, (also could be Kc or Keq) was derived from experimentation. For the reaction aA + bB ↔ cC + dD where lower case letters are coefficients and uppercase letters are chemical substances: K = [C]c[D]d [A]a[B]b this is the equilibrium expression Put more simply: K = [products]n [reactants]m MOST IMPORTANT  only AQUEOUS and GAS substances can go into the equilibrium expression WHY? [ ] is concentration and ONLY aq and g can change [ ] Molarity  Both aq and g depend on the volume in which they are contained  Pure solids and pure liquids do not have concentration measurements  therefore, their concentration values cannot change def: homogeneous equilibria – all substances in the reaction are in the same state def: heterogeneous equilibria – substances are in more than one state What does the Magnitude of K mean?  Larger K values indicates that the reaction really wants to (and does) occur, proceeds toward completion.  Smaller K values means that the reactants are favored, not many products will form. Ex. Write the homogenous equilibrium expression for the following reactions: a. Sulfur dioxide reacts with oxygen gas to form sulfur trioxide (all gases) Reaction: 2 SO2 + O2 ↔ 2 SO3 K = . [SO3]2 . [SO2]2[O2]1 b. Phosphorus pentachloride decomposes into chlorine and phosphorus trichloride (all gases) Reaction: PCl5 ↔ Cl2 + PCl3 K = [Cl2] [PCl3] [PCl5] 4 Ex. Write the heterogeneous equilibrium expression for the following reactions: a. Sulfur trioxide gas is bubbled into water producing sulfuric acid solution Reaction: SO3 (g) + H2O (l) ↔ H2SO4 (aq) K = [H2SO4] [SO3] LeChatelier’s Principle You will predict what changes occur when a system that is at equilibrium is disturbed, and you will suggest how to re‐establish equilibrium in that system. Back to EQUILIBRIUM POSITION – Dependent upon: ‐
Temperature ‐
Volume of container ‐
Concentrations of aq/g ‐
Pressure The position of a chemical reaction is said to ‐ lie to the LEFT if the reaction FAVORS the REACTANTS ‐ lie to the RIGHT if the reaction FAVORS the PRODUCTS LeChatelier’s Principle: When a change is imposed on a system at equilibrium, the position of equilibrium shifts in a direction to reduce the effect of that change 1. Effect of a Concentration change ‐ K remains constant  add a reactant/product, the system will shift AWAY from the added reactant/product  remove a reactant/product, sys will shift TOWARD the added reactant/product  system will compensate for addition or removal Ex: N2 (g) + 3H2 (g)  2NH3 (g) at equilibrium, disturb the system by: b. adding NH3 c. removing NH3 a. adding N2 → Right ← Left → Right Ex: CaCO3 (s)  CaO (s) + CO2 (g) at equilibrium, disturb the sys by: a. removing CO2 → Right b. adding CaO ← Left 5 c. adding CaCO3 → Right 2. Effect of changing Pressure ‐ K remains constant  add or remove gas reactant or product, same effect as concentration 3. Effect of changing Volume of container (Pressure increases and decreases)  both concentration and partial pressures of all sub change  when Volume deceases, the system responds by deceases the total number of molecules (that seems impossible, you can’t destroy matter)  the reaction system will respond by shifting to the side with the least number of gas molecules  when Volume increase, shift to side with most molecules, more space available, naturally take up that space Ex: N2 (g) + 3H2 (g)  2NH3 (g) at equilibrium, disturb the system by: 4 moles  2 moles a. decreasing volume of container ‐ shift to right, only 2 moles b. increasing volume of container ‐ shift to left, 4 moles Ex: CaCO3 (s)  CaO (s) + CO2 (g) at equilibrium, disturb the sys by: 1 moles  2 moles a. decreasing volume of container ‐ shift left, 0 gas molecules b. increasing volume of container ‐ shift right, 1 gas molecules 4. Effect of changing Temperature ‐ K changes with temperature change ‐ equilibrium constant K is constant for a given reaction at a certain temp;  Changing temp  treat ∆H as a reactant or product being added or released as temp changes  how? Recall:  endothermic reactions means Ea is being absorbed into the reaction to make it happen, “+” value, therefore add value to reactants side  exothermic reactions means Ea is being released from the reaction; “‐” value, therefore add value to products side Ex: N2 (g) + 3H2 (g)  2NH3 (g) ∆H = ‐92 kJ (exothermic) This is an exothermic reaction (negative value) add it to the products side N2 (g) + 3H2 (g)  2NH3 (g) + 92 kJ (exothermic) Disturb equilibrium by increasing Temp – Shift Left, away from addition (just like adding ammonia) ‐ Decrease Temp – Shift Right, toward removal 6 Ex: 2SO2 (g) + O2 (g)  2SO3 (g) ∆H = +198 kJ (endothermic) This is an endothermic reaction (+ value), add it to the reactant side, this much energy is needed to make the reaction go 2SO2 (g) + O2 (g) + 198 kJ ↔ 2SO3 ‐ increase temperature – shift R, away from addition (just like adding oxygen) ‐ decrease temperature – shift L, toward removal (just like removing oxygen) Now, evaluate how K changes as a result of temp change:  exothermic reactions ‐ Temperature increases, K decreases / T decreases, K increases  endothermic reaction ‐ T increases, K increases / T decreases, K decreases ‐ indicating that K increases, this means that the equilibrium position shift in favor of the products Larger K, reaction tends to proceed to completion LeChatelier’s Problem ∆H reaction = ‐58 kJ 2NO2 (g)  N2O4(g) When the following changes are imposed on the reaction system above, tell in which direction the equilibrium position will shift to re‐establish equilibrium: Change 1. Add N2O4 2. Remove N2O4 3. Add NO2 4. Remove NO2 5. Add Ne 6. Increase container vol 7. Decrease container vol 8. Increase pressure 9. Decrease pressure 10. Increase temp 11. Decrease temp Shift ← Left → Right → Right ← Left No Change ← Left → Right → Right ← Left ← Left → Right 7 (inert gas) (2 gas molecules vs. 1 gas mlc) (2NO2 (g) ↔ N2O4 + 58 kJ exo reaction) Name _________________________________
Equilibrium Constant (K) Date ____________________ Block ________
Write the expression for the equilibrium constant, K, for the reactions below. 1. N2 (g) + 3H2 (g) ↔ 2NH3 (g) K = . [NH3]2 . [N2] [H2]3 2. 2KClO3 (s) ↔ 2KCl (s) + 3O2 (g) K = [O2]3 3. H2O (l) ↔ H+ (aq) + OH‐ (aq) ‐
K = [H+] [OH ] 4. 2CO (g) + O2 (g) ↔ 2CO2 (g) K = . [CO2] 2 . [CO]2 [O2] 5. Li2CO3 (s)  2Li+ (aq) + CO3‐2 (aq) K = [Li+]2 [CO3‐2] Equilibrium and Kinetics Worksheet 1. What is kinetics? The study of reactions rates 2. Define activation energy? The energy required to start a reaction 3. Why do all reactions require activation energy? Reactions occur due to molecules/atoms colliding with each other and for that to happen energy is required. 4. Name 4 means of increasing the rate of a reaction. increasing the Temperature, increasing surface area, increasing concentration of the reactants, adding a catalyst. 8 5. Why will adding a catalyst speed up a reaction? It lowers the activation energy so less energy is required to start the reaction. 6. Define chemical equilibrium. A state when the concentration of all substances in a reaction remains constant (the rate of reactions are equal). 7. What does it mean for a reaction to go to completion? When the only thing in a reaction vessel that remains are the products and any excess reactants. 8. What does it mean for a reaction to be reversible? Most reactions are reversible because the reversible arrow indicates that a reaction can occur in either direction until equilibrium occurs. 9. What is the equilibrium expression? K = [C]c[D]d [A]a[B]b K = [products]n [reactants]m 10. What are the only two states that substances can be in to be a part of the equilibrium expression? Gas or aqueous substances (pure water, H2O, is not aqueous). 11. What do small K values indicate about a reaction? And a large K value? Small K means the reactants are favored (have higher concentrations), Large K means the products are favored (have higher concentrations). 12. What are the four changes that can be imposed on a system that is at equilibrium? (hint: LeChatelier’s principles) Change concentration, pressure, volume or temperature. 13. After an equilibrium system has been disturbed, will it come back to equilibrium? Yes, Lechatelier’s principle says that it will. 9 LeChatelier’s Principle LeChatelier’s Principle states that when a system at equilibrium is subjected to a stress, the system will shift its equilibrium point in order to relieve the stress. Complete the following chart by writing left, right, or none for equilibrium shift, and decreases, increases, or remains the same for the concentrations of the reactants and products, and for the value of K. N2 (g) + 3H2 (g) ↔ 2NH3 (g) ∆H=+ 22.0 kcal N2 (g) + 3H2 (g) + 22.0 kcal ↔ 2NH3 (g) Stress 1. Add N2 2. Add H2 3. Add NH3 Equilibrium Shift [N2] [H2] [NH3] Right _____
Decreases Increases Decreases _____ Increases Increases Increases _____ Right Left Remains the same omit
omit
4. Remove N2 Left _____ Increases Decreases Omit 5. Remove H2 Left Increases _____ Decreases Omit 6. Remove NH3 Right Decreases Decreases _____ Omit Decreases Decreases Increases Omit Increases Increases Decreases Omit Decreases Decreases Increases Omit Increases Increases Decreases Omit 7. Increase Temperature 8. Decrease Temperature 9. Increase Pressure 10. Decrease Pressure Right Left Right Left 10 K Acid/Base Notes: There are three types of acids and bases.
 Arrhenius acids and bases
 Acids- substances that will produce hydrogen ions (H + ) in solution
 Bases- substances that produce hydroxide ions (OH- ) in solution 3
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Brønsted- Lowry acids and bases Acids- molecule or ion that is a proton (H+ ) donor
 Bases- molecule or ion that is a proton (H+ ) acceptor
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Lewis acid and base
 Acids- lone pair acceptor
 Bases- lone pair donor
Strong Acids:
There are six strong acids that you’ll need to memorize for the SOL Chemistry test:
 Hydrohalic acids: HCl, HBr, HI
 Nitric acid: HNO3
 Sulfuric acid: H2SO4
 Perchloric acid: HClO4
Strong Bases:
NaOH KOH LiOH CsOH Ca(OH)2 Ba(OH)2 Sr(OH)2 Neutralization reactions:
 An acid will react with a base to produce water and a salt.
 Sodium hydroxide reacts with hydrochloric acid.
 Phosphoric acid reacts with calcium hydroxide. pH Scale
 pH is a measurement of the hydrogen ion
 pOH is a measurement of the hydroxide ion
 Every unit change in pH is a factor of 10 change in
concentration.
Acid/Base Calculations:
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Kw = [H+ ][OH ]
pH = -log[H+ ]
Kw = 1.0 x 10-14
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pOH = -log[OH ]
pH + pOH = 14
11 Practice: 1. For a 1.5M HBr solution, calculate the …
A. [H+]
pH = -log[H+ ]
pH = -log[1.5M]
pH = 0.18
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B. [OH ]
pH + pOH = 14
pOH = 14 - 0.18 pOH = 13.82
C. pH (assume 100% ionization)
pH = -log[H+ ]
pH = -log[1.5M]
pH = 0.18
HBr only has one H so it is considered 100% ionized.
D. pOH
pH + pOH = 14
pOH = 14 - 0.18 pOH = 13.82
HBr only has one H so it is considered 100% ionized.
2. For a 0.0500M H3PO4 solution, calculate the …
A. [H+ ]
pH = -log[H+ ]
-2
pH = -log[5.0 x10 M]
pH = 1.3
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B. [OH ]
pH + pOH = 14
pOH = 14 - 1.3 pOH = 12.7
C. pH (assume 100% ionization)
-2
pH = -log[H+ ]
pH = -log[(3 x 5.0 x10 M)]
pH = 0.82
H3PO4 has three H so it is considered is triple the concentration.
D. pOH
pH + pOH = 14
pOH = 14 – 0.82 pOH = 13.18
12 Unit 11‐12 Review Worksheets 1. Which of the following does not increase the rate of dissolving of a solute? a. Increasing Temperature of the solution b. Crushing the solute c. Stirring the solution d. All of the above improve the rate of dissolving of a solute 2. Breaking a solid into smaller pieces increases the rate of dissolving because a. It increases the temperature of the solution b. It increases the surface area of the solute c. It increases the energy of the solution d. It increases the pressure of the solution 3. Increasing the temperature of a solution a. Increases the frequency of solute – solvent collisions but decreases the energy b. Decreases the frequency of solute‐solvent collisions but increases the energy c. Decreases both the frequency and the energy of solute‐solvent collisions d. Increases both the frequency and the energy of solute‐solvent collisions 4. Which of the following will conduct an electric current? a. Sugar in water b. Alcohol in water c. Salt in water (It is an Ionic compound) d. Pure water 5. When a solid or gas dissolves easily in a liquid to form a solution, the solid or gas is said to be ________. a. Soluble c. Compatible d. Endothermic b. Heterogeneous 6. Which describes the chemical system that has reached equilibrium? a. the rates of the forward and reverse reactions are equal b. the concentrations of products and reactants are equal c. the reverse reaction has stopped d. the forward reaction has stopped 7. In the equilibrium system, 2SO2(g) + O2(g) ↔ 2SO3(g) + heat, the concentration of SO3 may be increased a. by increasing the concentration of SO2 b. by decreasing the concentration of SO2 c. by increasing the temperature. d. by decreasing the concentration of O2 13 8. Which change may occur when a catalyst is added to a reaction system? a. activation energy for the reaction decreases b. the heat of the reaction decreases c. the potential energy of the reactants increases d. the potential energy of the products decreases 9. Which statement explains why the speed of some chemical reactions is increased when the surface area of the reactants is increased? a. This change increases the density of the reactant particles b. This change increases the concentration of the reactant c. This change exposes more reactant particles to a possible collision d. This change alters the electrical conductivity of the reactant particles 10. Which describes the chemical system that has reached equilibrium? a. the rates of the forward and reverse reactions are equal b. the concentrations of products and reactants are equal c. the reverse reaction has stopped d. the forward reaction has stopped 11. In the equilibrium system, 2SO2(g) + O2(g) ↔ 2SO3(g) + heat, the concentration of SO3 may be increased Point B is the activation energy and e. by increasing the concentration of SO2 Point C is higher than Point A. It has b. by decreasing the concentration of SO2 more potential energy. c. by increasing the temperature. d. by decreasing the concentration of O2 12. Which phrase best describes the following reaction? 2H2O(l) + energy ↔ 2H2(g) + O2(g) a. exothermic, releasing energy b. exothermic, absorbing energy c. endothermic, releasing energy d. endothermic, absorbing energy Use The Diagram to the Right to answer Question 13 TO 15: 13. The diagram shows a reaction in which the reactants have_________ energy than the products a. less b. more c. the same amount d. none of the above 14. The diagram above shows a reaction in which energy has been_______ . a. released b. absorbed c. unchanged d. none of the above 15. The diagram above shows an example of a(an) _________reaction. a. A exothermic b. endothermic c. synthesis d. decomposition 14 16. In which reaction will the point of equilibrium shift to the left when the pressure on the system is increased? a. C(s) + O2(g) ↔ CO2(g) 2 to 1 ratio b. CaCO3(s) ↔ CaO(s) + CO2(g) 1 to 2 ratio c. 2Mg(s) + O2(g) ↔ 2MgO(s) 3 to 2 ratio d. 2H2(g) + O2(g) ↔ 2H2O(g) 2 to 2 ratio Pressure increasing favors the side with the least moles. 17. Which statement describes characteristics of an endothermic reaction? a. The sign of H is positive, and the products have less potential energy than the reactants. b. The sign of H is positive, and the products have more potential energy than the reactants. c. The sign of H is negative, and the products have less potential energy than the reactants. d. The sign of H is negative, and the products have more potential energy than the reactants. 18. Given the equilibrium system at 25°C: NH4Cl (s) ↔NH4+(aq) + Cl‐(aq) (ΔH = +3.5 kcal/mol) What change will shift the equilibrium to the right? a. decreasing the temperature to 15°C b. increasing the temperature to 35°C c. dissolving NaCl crystals in the equilibrium mixture d. stirring the equilibrium mixture Rewrite putting heat on reactant side because it is endothermic NH4Cl (s) + 3.5 kcal/mol ↔NH4+(aq) + Cl‐(aq) so increasing the temperature will be adding to reactants 19. Which of the following expressions is the correct equilibrium‐constant expression for the reaction below? answer A 15