CHEM 122 FINAL REVISED EXAM WITH CORRECTLY VERIFIED ANSWERS 2025

CHEM 122 FINAL REVISED EXAM WITH CORRECTLY VERIFIED ANSWERS 2025 Place a star next to the reaction that should have a ΔS value closest to zero. Underline the reaction(s) that should have an increase in entropy. a) 2NO (g) + O2 (g) -- 2NO2 (g) b) 2NO2 (g) -- N2 (g) + 2O2 (g) c) 2H2O (l) -- 2H2 (g) + O2 (g) d) C2H4O2 (l) + CH4O (l) -- C3H6O2 (l) + H2O (l) - Correct Ans-Starred: D Underlined: B & C Predict the sign of hte entorpy change for the following processes. a) Exhaled breath forms fog on a cold morning. ______________ b) Snow melts. ________________ - Correct Ans-a) negative (-) b) positive (+) A reaction has ΔH° (298) = 100 KJ/mol and ΔS° (298) = 250 J/mol*K. Is the reaction spontaneous at room temperature? If not, under what temperature conditions will it become spontaneous? - Correct Ans-It is not spontaneous, but will be spontaneous at 400 K or 127°C. Given the standard entorpies (ΔS) for the folloing reaction, calculate the ENTHALPY (ΔH) change for the reaction at 25.0°C. Mg (s) + 2 HF (g) - MgF2 (s) + H2 (g) S° J/mol*K Mg = 32.69 2HF = 173.7 MgF2 = 57.24 H2 = 114.6 - Correct Ans-ΔH = -644 KJ As the temperature of a block of ice is increased from 200. K to 220. K, would you expect the entropy to increase or decrease, and why? - Correct Ans-Temperature increased from -73°C to -53°C so the entropy increases. Consider the reaction represented below, which is spontaneous at 298 K. 2NH3 (g) + CO2 (g) -- CO(NH2)2 + H2O (l) CHEM 122 CHEM 122 ΔH° (298) = -134 kJ a) For the reaction, indicate whether the standard entropy changes, ΔS° (298), is positive, or negative, or zero. b) Which factor, the change in enthalpy, ΔH° (298), or the change in entropy, ΔS° (298), provides the principle driving forces for the reaction at 298 K? - Correct Ans-a) Negative b) Enthanlpy Driven When potassium nitrate is dissolved in water, the resulting solution is significantly colder than the water was originally. a) Is the dissolution of potassium nitrate an endothermic or an exothermic process? b) What conclusions can you draw about the intermolecular attractions involved in the process? - Correct Ans-a) Endothermic b) The solute-solute & solvent-solvent interactions are greater than the solute-solvent interactions. Explain Why CH3CH2CH2CH2CH2OH is insoluble in water whereas HOCH2CH2CH2CH2CH2OH is soluble in water. - Correct Ans-The insoluble compound has too many carbons which has LDF. Not soluble, but the soluble has a second OH on the other end which gives the molecule enough polarity to be soluble. If 84.44g of NaCl was dissolved in 1.44L of water (density = 1.000 g/mL), what will be the freezing point? The Kf for water is 1.86 °C/m. - Correct Ans-Freezing Point = 3.37°C The Henry's law constant for O2 is 1.3 x 10^-3 M/atm at 25°C. Assuming ideal solution behavior, what mass of oxygen would be dissolved in a 40L aquarium at 25°C, assuming an atmospheric pressure of 1.00 atm, and that the partial pressure of O2 is 0.21 atm? - Correct Ans-0.35g O2 A solution for sodium chloride for intravenous injection contains 0.86g of NaCl in 10.00 x10^2g of water, calculate the mole fraction and the molarity of solution. a) Calculate the mole fraction of solution. b) Calculate the molarity of solution. - Correct Ans-a) x = 2.64 x 10^-3 b) 0.15 m CHEM 122 CHEM 122 Why does 1 mol of sodium chloride depress the freezing point of 1 kg of water almost twice as much as 1 mol of glycerin? - Correct Ans-Glycerin has an "i" value of 1 whereas sodium chloride has an "i" value of 2. Assuming ideal solution behavior, what is osmotic pressure of a solution of bovine insulin (5700g/mol) at 18°C if 100.0mL of the solution contains 0.103g of the insulin? - Correct Ans-π = 0.0043 atm Lysozyme is an enzyme that cleaves cell walls. A 0.100L sample of a solution of lysozyme that contains 0.0750g of the enzyme exhibits an osmotic pressure of 1.32 x 10^-3 atm at 25°C. Assuming ideal solution behavior, what is the molar mass of lysozyme? - Correct Ans-MM = 1.39 x 10^4 g/mol or 13900 g/mol What is the overall order of the reaction NO2(g) + CO (g) -- NO (g) + CO2 (g) If it proceeds via the following expression? Rate = k [CO][NO] a) zero-order b) first-order c) second-order d) third-order e) fourth-order - Correct Ans-C Ammonia can be formed by reacting nitrogen and hydrogen gases. N2 (g) + 3 H2 (g) -- 2 NH3 (g) If the rate of disappearance of hydrogen is -2.7 x 10^-2 M/s, what is the rat of formation of ammonia? a) 1.8 x 10^-2 M/s b) 2.7 x 10^-2 M/s c) 4.0 x 10^-2 M/s d) 5.4 x 10^-2 M/s e) 8.1 x 10^-2 M/s - Correct Ans-A For the reaction 2 C2F4 -- C4F8, a graph gives a straight line with a slope of 0.04/Ms. Write a full rate law for this reaction? - Correct Ans-Rate = 0.04/M*s [C2F4]^2 CHEM 122 Explain the effect a catalyst has on the activation energy and the reaction rate. - Correct Ans-The catalyst lowers the activation energy. This allows the reaction to go fatser. A mixture of 0.200 mole NO and 0.200 mole CO2 is placed in a 1.00L flask and allowed to reach equilibrium at a given temperature. Analysis of the equilibrium mixture indicates that 0.076 mole of Co is present. Calculate Kc for the reaction. - Correct Ans-Kc = 3.76 x 10^-1 For the following reaction at equilibrium, which choice gives a change that will shift the position of equilibrium to favor formation of more products? 2NOBr (g) ==== 2No (g) + Br2 (g) ΔH° (rxn) = 30 kJ/mol a) Increase the total pressure by decreasing the volume. b) Add more NO c) Add Br2 d) Add more NOBr - Correct Ans-D An acid is classified weak a) only in a concentrated solution b) if its equilibrium is between 0 and 1 c) if it forms a salt with NaOH d) if it ionizes almost completely in solution - Correct Ans-B Given Kw = 1.0 x 10^-14, what is the [OH-] in a solution whose [H+] is 2.0 x 10^-5 M? a) 2.0 x 10^-10 M b) 5.0 x 10^10 M c) 2.0 x 10^-5 M d) 2.0 x 10^9 M - Correct Ans-B One product of the reaction between KOH and HBr is a) OH- b) H2O c) H2 d) Br2 - Correct Ans-B What is the pH of a solution that has a [Oh-] of 0.1 M? a) 1 b) 7 c) 12 d) 13 - Correct Ans-D CHEM 122 CHEM 122 What acid yields the greatest [H+]? a) 1 M Phosphoric acid Ka=7.5 x 10^-3 b) 1 M Benzoic acid Ka = 6.6 x 10^-5 c) 1 M Hydrofluoric acid Ka=7.2x10^-4 d) 1 M Carbonic acid Ka = 4.2 x 10^-7 - Correct Ans-A Which compound or ion cannot act as a Bronsted-Lowery Base? a) H2O b) NH3 c) NH4+ d) HCO3^- - Correct Ans-C Which aqueous solution is the least acidic? a) pH = 6.4 b) [H+] = 2 x 10^-7 M c) [OH-] = 2 x 10^-9 M d) pOH = 8.2 - Correct Ans-B What is the pH of a 0.020 M solution of a weak monoprotic acid if 4.0% of it ionizes? - Correct Ans-pH = 3.1 When a 50 mL of 0.01 M NaF is added to 50 mL of 0.10 M HF, compared tot he pH of the 0.1 M HF solution the pH of the resulting solution will... a) become 7 b) decrease c) increase d) remain the same - Correct Ans-C Which reaction is NOT a redox reaction? a) 2Na + 2H2O -- 2NaOH + H2 b) 2 Fe + 3S -- Fe2S3 c) H2 + O2 -- H20 d) H^+ + H2O-- H3O^+ - Correct Ans-D In a galvanic cell, the cathode has a _________ sign and is the site of __________. a) negative, oxidation b) negative, reduction c) positive, oxidation d) positive, reduction - Correct Ans-D