Due Date: First day of school if you miss the first day of school, you must send a scanned/pdf copy to Mr. Mejia:

Transcription

1 Name: Date: AP Chemistry Summer Assignment Due Date: First day of school if you miss the first day of school, you must send a scanned/pdf copy to Mr. Mejia: jmejia@cboek12.org Assessment: Within the first week of school you are responsible for all topics/ questions within the summer assignment. Answers must include work and be handwritten to receive credit. The assignment is designed to have you recall things you have learned in previous classes, especially Chemistry, in order to prepare you for AP Chemistry. You will need to have a good grasp of the foundations of Chemistry such as states of matter, types of reaction, balancing, and stoichiometry (including limiting reagents), and many more. AP Chemistry is a college-level course, and the College Board recommends that each student take a minimum of 6 hours of review each day outside of the classroom. It is also highly recommended that each student acquires a test-prep book as early as possible. There are many test-prep books out there, and you are welcome to contact me if you are looking for recommended names. You are expected to know the list of common polyatomic ions and the solubility rules. Common Polyatomic Ions Nitrate NO3 1 (Hy)perchlorate ClO4 Nitrite NO2 1 Chlorate ClO3 Carbonate CO3 2 Chlorite ClO2 1 Carbonite CO2 2 Hypochlorite ClO 1 Sulfate SO4 2 Hydroxide OH 1 Sulfite SO3 2 Acetate C2H3O2 1 CH3COO 1 Phosphate PO4 3 Permanganate MnO4 1 or Phosphite PO3 3 Ammonium NH4 +1

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46 Le Châtelier s Principle Chem Worksheet 18-6 Name A stress that is applied to a reaction that is at equilibrium conditions will shift the equilibrium position in a direction that tends to reduce this stress. This concept was first described by Le Châtelier. A reaction can be stressed by changing the concentration of a reactant or product, changing the volume, and changing the temperature. Each stress tends to either favor the forward or reverse reaction until a new equilibrium position is established. If the forward reaction is increased we say equilibrium shifts to the right, and if the reverse reaction is increased equilibrium shifts to the left. When the concentration of a gaseous or aqueous reactant or product is increased the equilibrium reaction shifts in the direction that decreases the concentration of that substance. If more product is added to a system at equilibrium, the reverse reaction increases in order to use the extra product, shifting equilibrium to the left. When the volume is reduced the equilibrium reaction shifts toward the side that contains the fewest gas particles. An increase in volume shifts to the side with the most gas particles. An increase in temperature will favor a reaction that is endothermic. A decrease in temperature will favor the reaction that is exothermic. Concentration Changed 2A (g) + 3B (g) 2C (g) + D (g) Temp. Changed for Endothermic Rxn. A (g) + B (g) + heat C (g) + D (g) Action Increase [A] Increase [C] Decrease [B] Decrease [C] Effect Shift to the right Shift to the left Shift to the left Shift to the right Action Increase Temp. Decrease Temp. Effect Shifts to right (endothermic rxn.) Shifts to left (exothermic rxn.) Volume Changed 2A (g) + 3B (g) 2C (g) + D (g) Temp. Changed for Exothermic Rxn. A (g) + B (g) C (g) + D (g) + heat Action Volume decreased Volume increased Effect Shifts to right (side with fewest gases) Shifts to left (side with most gases) Action Increase Temp. Decrease Temp Effect Shifts to left (endothermic rxn.) Shifts to right (exothermic rxn.) Predict the direction equilibrium will shift when the following stresses occur. Explain your prediction. Assume each reaction occurs in a sealed container and has reached equilibrium. 1. NO 2 is added to the system. 2. N 2 is added to the system. 3. O 2 is removed from the system. 2NO 2 (g) N 2 (g) + 2O 2 (g) H = + 33 kj/mol (endothermic) 4. The temperature of the container is increased. 5. The volume of the container is increased. 6. N 2 is added and NO 2 is removed. 7. CO 2 is added to the system. 8. The volume of the container is decreased. 9. CaO is removed from the system. CaCO 3 (s) CaO (s) + CO 2 (g) H = kj/mol (endothermic) 10. The temperature of the container is decreased. 11. The volume of the container is increased. 12. CaCO 3 is added to the system. 13. H 2 is removed from the system. 14. HCl is removed from the system. 15. The volume of the container is increased. H 2 (g) + Cl 2 (g) 2HCl (g) H = 185 kj/mol (exothermic) 16. The temperature of the container is increased. 17. The concentration is Cl 2 is decreased. 18. The volume of the container is decreased. John Erickson, 2005 WS18-6LeChatelier

47 Kinetics and Reaction Rates How to talk about Reaction Rate rate = [chemical]/ time Common Units: M/s, mol L-1 s-1 rate of disappearance of reactant or rate of appearance of product use coefficients to change one rate to another Reaction: 2A + 3B 4C 1 [A] 1 [B] 1 [C] 2 = 3 = 4 t t t watch your signs ( [React.] = - [Prod.]) From a graph of [R] vs time Average rate is the slope of a segment. Instantaneous rate is slope of the tangent. Initial rate is often used. How to Speed Up a Reaction [Use Collision Theory, Kinetic Molecular Theory] increase the concentration of reactants - increase molarity of solutions - increase partial pressure of gases [collision model: more collisions] more surface area between unlike phases [collision model: more collisions] increase the temperature [collision model: more & harder collisions] add a catalyst - homogeneous catalyst (used & reformed) - heterogeneous catalyst (surface catalyst) [collision model: alternate mechanism that requires lower energy collision or ensures that correct particles collide] Because Rate depends on Concentration Rate Laws - what they mean - how to determine them - how they relate to the rate determining step - how they help you choose a mechanism General Form: Equation: A + B C Rate = k [A] x [B] y experimentally because the rate law reflects only the rate determining step. Rate law can be determined from initial rates. See Example 15.3 and Exercise 15.3 Rate Law matches the Molecularity of the Rate Determining Step in the Mechanism Examples for: 2A + 3B C (fill in from lecture) Rate Determining Step Rate Law in the mechanism Rate = k [A][B] Rate = k [A] 2 Rate = k [A] 2 [B] Rate = k A + B X (slow) A + A X (slow) A + A X (fast) B + X Y (slow) Each step is usually bimolecular. A third order overall reaction often comes from a fast equilibrium before a slow step. This could be a mechanism that depends on a catalyst only. The concentrations would not matter. order of rxn - first and second order reactions - what these look like graphically - how you can graphically tell the order of a reaction order straight-line plot Slope 0 [R]t vs. t -k 1 ln[r]t vs. t -k 2 1/[R]t vs. t k - how this relates to the rate law k is the specific rate constant Use experimental data to determine x, y, and k. The Rate Law CANNOT be determined from the overall reaction. It MUST be determined

48 Two Important Diagrams PE energy profile of a reaction PE a b c reaction coordinate H of the reaction relates reactant and product PE s / exo- or endothermic/ downhill, - H, or uphill, + H activation energy (Ea) = energy barrier activated complex (at the peak) whether a reaction is fast or slow depends on the activation energy in the PE profile PE profile does not change with change in temperature of the reactants? adding a catalyst lowers the Ea The KE distribution of a substance KE d e threshold energy - temperature is the average KE -increasing temperature spreads out curve to the right, increases average KE KE threshold energy - adding a catalyst moves the threshold energy to the left. KE threshold energy How do these two picture relate to each other (turn the KE on its side... the particles use their KE to provide the needed PE to react) Reaction mechanisms - step-by-step...two particles at a time - example overall: 4 HBr + O 2 2 Br H 2 O mechanism: HBr + O 2 HOOBr HOOBr + HBr 2 HOBr HOBr + HBr Br 2 + H 2 O HOBr + HBr Br 2 + H 2 O [note: HOOBr and HOBr are not in the overall reaction because they are neither reactants nor products, they are reactive intermediates ] - overall reaction is sum of steps - slowest step is rate-determining step half-life - relationship to radioactivity (a first order reaction) - the equation [ A] ln o kt [ A] t - the special case of half-life ln(2) = = kt½ chain reactions (fill in from lecture & video) - initiation steps - propagation steps - termination steps examples: - H 2 + Cl 2 2 HCl - polymerization reactions (addition) - ozone depletion ozone layer - specifics on why CFC s are dangerous to the ozone layer and are economically desirable here on the surface Determining Ea from calculations using the Arrhenius Equation

49 For the following reactions: a. Determine the reaction order with respect to each reactant. b. Determine the overall reaction order. c. Write the rate law. d. Calculate the value of the rate law constant. e. Determine the units of the rate law constant. (note the reaction rate units) Describe the Collision Model/Theory and why it is important to Chemistry/Chemical Kinetics. AP Kinetics - Mechanisms Write rate laws which correspond to the following mechanisms. Also write the overall reaction and circle any intermediates. 1. O3 O2 + O (k1/k-1 fast) O + O3 2 O2 (k2 slow) 2. H2 + ICl HI + HCl (k1 slow) HI + ICl I2 + HCl (k2 fast) 3. Cl2 2 Cl (k1/k-1 fast) Cl + CHCl3 HCl + CCl3 (k2 slow) CCl3 + Cl CCl4 (k3 fast)

50 IMF s, Liquids and Solids 1. Describe the intermolecular forces at work in the following: a. within a water molecule H2O b. in a crystal of the salt NaCl c. in a solution of potassium nitrate KNO3 d. in diamond e. in a fiber of nylon f. in liquid butane g. between water molecules in ice h. between the two strands in the double helix of DNA i. in paraffin wax j. between the molecules of carbon dioxide CO2 in dry ice k. between the molecules of HCl in liquid HCl l. in tungsten metal m. in a solution of perchloric acid 2. Which one of the following pairs of molecules would you expect to have the higher melting point? a. Cl2 or Br2 b. C4H10 or C5H12 c. NH3 or PH3 d. Na or Mg e. BeO or KCl f. ICl or Br2 3. Which states or types of matter would be characterized by each of the following statements? a. High individual molecular speeds. b. A melting point spread over a wide temperature range. c. A regular repeating array of structural units. d. Molecules move with respect to one another but are held together in a condensed state. e. Molecules close together but having sufficiently high kinetic energies to overcome the intermolecular forces. f. Valence electrons delocalized over huge arrays of atoms. g. Totally random molecular order with comparatively great distances between individual molecules. h. A three-dimensional network of covalent bonds. 4. Acetone and chloroform form an unusually strong intermolecular bond. Why is this? Draw a picture of how the molecules attract each other. 5. a. How much heat is required to melt 15 grams of ice at 0 C? b. How much heat is released when 100 grams of steam condenses at 100 C? c. If a system of ice and water has a mass of 12 grams, and it is converted completely to water at 0.0 C by supplying 1.33 kj of heat, how much water was initially present? Heat of fusion of ice = 333 J/g Heat of vaporization of water = 2250 J/g