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)

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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) ∆𝐻𝑟𝑥𝑛 = −29.0𝑘𝐽 ° O3(g) 32O2(g) ∆𝐻𝑟𝑥𝑛 = 24.18𝑘𝐽

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)

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4)

6 pts

Determine the mass of CO2 produced by burning enough C3H8 to produce 1.00×102 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 𝑘𝐽 combustion of the fuel? Report your answer in 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)

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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 𝑘𝐽 is established. Given ∆𝐺𝑓° (𝐵𝑟𝐶𝑙(𝑔)) = −0.98𝑚𝑜𝑙 , and 𝑘𝐽 ° ∆𝐺𝑓 (𝐵𝑟2 (𝑔)) = 3.11𝑚𝑜𝑙.

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2)

17 pts

In a coffee cup calorimeter 50.0 mL of 0.100 M AgNO3 and 50.0 mL of 0.100 M HCl are mixed. The following reaction occurs: Ag+(aq) + Cl-(aq)  AgCl(s) If the two solutions are initially at 22.60˚C, and if the final temperature is 𝑘𝐽 23.40˚C, calculate ΔH for the reaction in 𝑚𝑜𝑙 of AgCl formed. Assume a mass of 100.0 g for the combined solution and a specific heat capacity of 𝐽 4.18 ℃∙𝑔 .

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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 KJ B) -95.7 KJ C) -28,500 KJ D) 28,500 KJ 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

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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

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