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NAME: ______________________________________ CHEM 121A Spring 2024 (PRINT, last name first) EXAM #3 (100 pts) Mar. 14, 2024
Remove the last page, and use it for scratch paper and to cover your work. That page contains a copy of the periodic table.
1. Calculate the amount of heat (in kJ) necessary to raise the temperature of 55.8 g benzene by 48.8 K. The specific heat capacity of benzene is 1.05 J/g°C.
A) 1.81 kJ B) 3.89 kJ C) 2.79 kJ D) 2.86 kJ E) 20.6 kJ
2. Which of the following signs on q and w represent a system that is doing work on the surroundings, as well as losing heat to the surroundings?
A) q = -, w = - B) q = +, w = - C) q = -, w = + D) q = +, w = + ‘E) None of these represent the system referenced above
3. A 2.49 g sample of aniline (C 6 H 5 NH 2 , molar mass = 93.13 g/mol) was combusted in a bomb calorimeter with a heat capacity of 4.25 kJ/°C. If the temperature rose from 29.5°C to 69.8°C, determine the value of ΔH° comb for aniline.
A) +6.40 × 10 3 kJ/mol B) -1.71 × 10^3 kJ/mol C) -3.20 × 10 3 kJ/mol D) +1.71 × 10 3 kJ/mol E) -6.40 × 10 3 kJ/mol
4. Define heat.
A) the flow of energy caused by a chemical reaction B) the capacity to do work C) the result of a force acting through a distance D) a chemical reaction E) the flow of energy caused by a temperature difference
5. The value of ΔH° for the reaction below is -482 kJ. Calculate the heat (kJ) released to the surroundings when 10.0 g of CO (g) (MM=28.0 g/mol) reacts completely.
2CO (g) + O 2 (g) → 2CO 2 (g)
A) 172 kJ B) 482 kJ C) 2410 kJ D) -482 kJ E) 86.0 kJ
6. Given the data in the table below, ΔH°rxn for the reaction Substance ΔH˚f (kJ/mol) Ca(OH) 2 -986. H 3 AsO 4 -900. Ca(H 2 AsO 4 ) 2 -2346. H 2 O -285. Ca(OH) 2 + 2H 3 AsO 4 → Ca(H 2 AsO 4 ) 2 + 2H 2 O is ________ kJ.
A) -76.4 B) -4519 C) -4219 D) -744.9 E) -130.
7. Given the following reactions: Fe 2 O 3 (s) + 3CO (s) → 2Fe (s) + 3CO 2 (g) ΔH = -28.0 kJ 3Fe (s) + 4CO 2 (s) → 4CO (g) + Fe 3 O 4 (s) ΔH = +12.5 kJ the enthalpy of the reaction of Fe2O3 with CO 3Fe 2 O 3 (s) + CO (g) → CO 2 (g) + 2Fe 3 O 4 (s) is ________ kJ. A) -59.0 B) +109 C) -109 D) -15.5 E) 40. 8. A ________ΔH corresponds to an _________process.
A) negative, endothermic B) negative, exothermic C) positive, exothermic D) zero, exothermic E) zero, endothermic
9. Define specific heat capacity. A) the quantity of heat required to raise the temperature of 1 liter of a substance by 1° C B) the quantity of heat required to raise the temperature of 1 gram of a substance by 1°F C) the quantity of heat required to raise the temperature of 1 mole of a substance by 1° C D) the quantity of heat required to change a system's temperature by 1°C E) the quantity of heat required to raise the temperature of 1 gram of a substance by 1°C 10. The approximate value of ΔH for a reaction can be found by appropriate combination of bond enthalpies (the energy required to break a particular bond, represented by BE). Which expression will give the approximate value for ΔH for the following reaction? C 2 H 4 (g) + H 2 (g) ---> C 2 H 6 (g) A) ½BEC=C + BEH−H − 2BEC−H B) BEC−C + 2BEC−H − [BEC=C + BEH−H] C) BEC=C + BEH−H − [BEC−C + 2BEC−H] D) 2BEC−H − ½BEC=C + BEH−H 11. KUNR broadcasts at a frequency of 88.7 MHz. What is the wavelength of this radiation? A) 3.38 x 10^6 m B) 3.38 x 10^3 m
C) They have different sizes D) They hold a different number of electrons
25. The angular momentum quantum number (l) value of 2 indicates the ________ subshell.
A) s B) +1/ C) f D) d E) p
