Chem. 1B Midterm 1 Practice Test 1

Transcription

1 Chem. 1B Midterm 1 Practice Test 1 Name Student Number All work must be shown on the exam for partial credit. Points will be taken off for incorrect or no units. Calculators are allowed. Cell phones may not be used for calculators. On fundamental and short answer problems you must show your work in order to receive credit for the problem. If your cell phone goes off during the exam you will have your exam removed from you. Fundamentals (of 36 possible) Problem 1 (of 17 possible) Problem 2 (of 17 possible) Multiple Choice (of 30 possible) Midterm Total (of 100 possible) 1

2 Fundamental Questions Each of these fundamental chemistry questions is worth 5 points. You must show work to get credit. Little to no partial credit will be rewarded. Make sure to include the correct units on your answers. 1) 6 pts A 20.0 g of Al at 120. C is placed in 100. g of water at 25 C. What is the final temperature of system? Assume that no heat leaves the system. 2) 6 pts Determine the value of the heat of reaction for the following: Cl(g) +O3(g) ClO(g) + O2(g) Given: ClO(g) + O3(g) Cl(g) + 2O2(g) H rxn = 29.0kJ O3(g) 3 O2(g) 2 = 24.18kJ H rxn 3) 6 pts A chemist fills a reaction vessel with 6.13 atm nitrogen (N2) gas, 7.94 atm hydrogen (H2) gas and 8.47 atm ammonia (NH3) gas at a temperature of 137 C. Under these conditions, calculate the reaction free energy for the following chemical reaction: N2(g) + 3H2(g) 2NH3(g) 2

3 4) 6 pts Determine the mass of CO2 produced by burning enough C3H8 to produce kj of heat. C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g) ΔHrxn=-2217 kj 5) 6 pts When 1 mol of a fuel burns at constant pressure it produces 3452 kj of heat and does 11 kj of work. What are the values of ΔE and ΔH for the combustion of the fuel? Report your answer in kj mol 6) 6 pts Calculate ΔG at 125 C for the following reaction. Assume that ΔH and ΔS are temperature independent. 2CH3OH(g) +3O2(g) 2CO2(g) + 4H2O(l) 3

4 Short Answer Questions Each of the following short answer questions are worth the noted points. Partial credit will be given. You must show your work to get credit. Make sure include proper units on your answer. 1) 17 pts At 298 K, 1.00 mol BrCl(g) is introduced into a 10.0 L vessel, and equilibrium is established in the reaction BrCl(g) ½Br2(g) + ½Cl2(g) Calculate the amounts of each of the three gases present when equilibrium is established. Given G f (BrCl(g)) = 0.98 kj mol G f (Br 2 (g)) = 3.11 kj mol 4

5 2) 17 pts In a coffee cup calorimeter 50.0 ml of M AgNO3 and 50.0 ml of M HCl are mixed. The following reaction occurs: Ag + (aq) + Cl - (aq) AgCl(s) If the two solutions are initially at C, and if the final temperature is C, calculate ΔH for the reaction in kj of AgCl formed. Assume a mol mass of g for the combined solution and a specific heat capacity of 4.18 J g 5

6 Multiple Choice Questions Each of the following multiple choice questions are worth 5 points. Your answers need to be filled in on the Scantron provided. Note: Your Scantrons will not be returned to you, therefore, for your records, you may want to mark your answers on this sheet. On the Scantron you need to fill in your perm number, test version, and name. Failure to do any of these things will result in the loss of 1 point. Your perm number is placed and bubbled in under the ID number. Do not skip boxes or put in a hyphen. In addition, leave bubbles blank under any unused boxes. The version number (B) is bubbled in under the test form. 1. Which of the following statements is(are) true? A) The heat of reaction and change in enthalpy can always be used interchangeably. B) A chemist takes the point of view of the surroundings when determining the sign for work or heat. C) Enthalpy is a state function. D) At least two of these statements are true. E) In exothermic reactions, the reactants are lower in potential energy than the products. 2. Calculate the S associated with a process in which 5.00 mol of ideal gas expands reversibly at constant temperature T=25 C from a pressure of 10.0 atm to 1.00 atm. A) 95.7 J K B) J K C) -28,500 J K D) 28,500 J K E) None of the above 3. The heat combustion of acetylene, C2H2(g), at 25 C, is 1299 kj/mol. At this temperature, H f values for CO2(g) and H2O(l) are 393 and 286 kj/mol, respectively. Calculate H f for acetylene. A) 625 kj/mol B) 227 kj/mol C) 2376 kj/mol D) 625 kj/mol E) none of these 6

7 4. When a student performs an endothermic reaction in a calorimeter, how (if any) does the calculated value of H differ from the actual value if the heat exchanged with the calorimeter is not taken into account? A) Hcalc equals the actual value because the calorimeter does not absorb heat. B) Hcalc is more positive because the reaction absorbs heat from the calorimeter. C) Hcalc is more negative because the calorimeter always absorbs heat from the reaction. D) Hcalc is less negative because the calorimeter absorbs heat from the reaction. E) Hcalc is less positive because the reaction absorbs heat from the calorimeter. 5. Which of the following result(s) in an increase in the entropy of the system? I. (See diagram.) II. Br2(g) Br2(l) III. NaBr(s) Na + (aq) + Br (aq) IV. O2(298 K) O2(373 K) V. NH3(1 atm, 298 K) NH3(3 atm, 298 K) A) II, V B) I, II, III, V C) I, II, III, IV D) I E) I, III, IV 6. Consider the freezing of liquid water at 10 C. For this process what are the signs for H, S, and G, respectively? A) + B) + C) + 0 D) E) + 0 7