Dr. Maples Exam 3 Review

Thermochemistry

100

What is the change in internal energy of a system that does 467 kJ of work and loses 157 kJ of heat to the surrounding?

A) 310 kJ

B) -624 kJ

C) -310 kJ

D) 624 kJ

B) -624 kJ

200

Water can be formed from the reaction of gaseous hydrogen and oxygen below. How many joules of heat are released from reacting 50.0 g H_{2 (g)}?

2 H_2 (g) + O_{2 (g)}  →  2 H₂O _(l)    ΔH= -572 kJ

A. 1140 J

B) 2860 J

C) 5720 J

D) 57200 J

E) 7093254 J

E) 7093254 J

300

Calculate the enthalpy ΔHrxn for the following reaction.

2 SO_{2 (g)} + O_{2 (g)} →  2 SO_{3 (g)}       ΔH_rxn = ?

given the following ΔH values

S _(s) + O_{2 (g)} →  SO_{2 (g)}      ΔH = -299 kJ

S _(s) + 3/2 O_{2 (g)} →  SO_{3 (g)}    ΔH = -395 kJ

A) -694 kJ

B) 1388 kJ

C) -192 kJ

D) 192 kJ

E) -1388

C) -192 kJ

400

A system releases 23.5 kJ as heat and undergoes a volume change from 10.5 L to 23.8 L under a constant external pressure of 1.25 atm. Calculate ΔE for this process. Note: 1.00 L . atm = 101.325 J.

a) -25.2 kJ

b) -21.8 kJ

c) 17.1 kJ

d) 25.6 kJ

a) -25.2 kJ

500

Use the enthalpy of formation data in the table to calculate the change in enthalpy, ΔH, of the reaction below.

2 H_{2 S (g)} + 3 O_{2 (g)} → 2 H₂O _(l) + 2 SO₂

(See table)

A) -561.2 kJ

B) -1123.5 kJ

C) -1144.6 kJ

D) 603.2 kJ

B) -1123.5 kJ

Calorimetry

100

Which of the following would show the largest temperature change upon heating with 700 J of heat?

A) a 1.0 kg aluminum pan (c = 0.90 J/g°C)

B) a 2.0 kg copper pot (c = 0.39 J/g°C)

C) a 1.0 kg iron skillet (c = 0.45 J/g°C)

D) a 2.0 kg concrete slab (c = 0.88 J/g°C)

E) a 1.0 kg glass bowl (c = 0.84 J/g°C)

C) a 1.0 kg iron skillet (c = 0.45 J/g°C)

200

How much energy is needed to heat 750 g of pure water from 20.0°C to 100.0°C?

(C _water = 4.184 J/g°C)

A) 251.0 kJ

B) 502.5 kJ

C) 394.2 kJ

D) 435.0 kJ

E) 315.3 kJ

A) 251.0 kJ

300

A 2.67 g sample of a metal is warmed to 73.8°C and submerged in 15.5 g of water initially at 24.7°C. The final temperature of the mixture is at 26.9°C. What is the specific heat capacity of the unknown metal? 

(C_water = 4.184 J/g°C)

A) 8.13 J/g·°C

B) 24.3 J/g·°C

C) 0.518 J/g·°C

D) 1.14 J/g·°C

E) 2.16 J/g·°C

D) 1.14 J/g·°C

400

A 55.3 g sample of ammonium nitrate NH₄NO₃ is dissolved in 132.0 g of water in a coffee-cup calorimeter. Upon dissolution the temperature changes from 24.3 ºC to 5.6 ºC. Calculate ΔH for the formation of this solution in units of kJ/mol ammonium nitrate, given that the heat capacity of the final solution is 4.22 J/g•ºC. Assume no heat is lost to the surroundings or the calorimeter. The molecular weight of NH₄NO₃ is 80.04 g/mol.

a). +14.8 kJ/mol NH₄NO₃

b). +15.1 kJ/mol NH₄NO₃

c). – 19.8 kJ/mol NH₄NO₃

d). + 21.4 kJ/mol NH₄NO₃

d). + 21.4 kJ/mol NH₄NO₃

500

A 1.255 g sample of fructose, C₆H₁₂O₆ (180.18 g/mol), is ignited in the presence of excess O₂ inside a bomb calorimeter. The temperature increased from 15.7°C to 27.2°C. Given that the heat capacity of the calorimeter is 805.4 J/°C, determine ΔU_rxn for the combustion of fructose in units of kJ/mol of fructose.

C₆H₁₂O_{6 (s)} + 6 O_{2 (g)}  → 6 CO_{2 (g)} + 6 H₂O _(l)

A) +1670 kJ/mol

B) -11.6 kJ/mol

C) +1330 kJ/mol

D) -1330 kJ/mol

E) -1670 kJ/mol

D) -1330 kJ/mol

Gas Laws

100

A 5.0 L sample of nitrogen gas has a pressure of 0.350 atm. What is the volume if the pressure is increased to 0.750 atm at constant temperature?

A) 2.33 L

B) 3.33 L

C) 4.00 L

D) 7.14 L

A) 2.33 L

200

A 135 mL sample of gas is heated from 265 K to 435 K. What will the final volume of the gas be if the pressure remains constant?

A) 82.2 mL

B) 170 mL

C) 222 mL

D) 854 mL

C) 222 mL

300

A 250 mL sample of helium at 0°C is heated at constant pressure to give a final volume of 435 mL. What is the final temperature (K) of the helium sample?

A) 150 K

B) 273 K

C) 310 K

D) 475 K

D) 475 K

400

A 22.0 g sample of gaseous carbon dioxide has a volume of 15.3 L. What will be the new volume if an additional 15.0 g carbon dioxide gas are added at constant temperature and pressure?

A) 10.4 L

B) 22.4 L

C) 25.7 L

D) 35.3 L

C) 25.7 L

500

What is the final temperature (°C) of a sample of xenon gas, originally at 25°C, if the volume is halved and the pressure triples?

A) 447 °C

B) -223 °C

C) 174 °C

D) 50 °C

E) 37.5 °C

C) 174 °C

Gas Behavior

100

If you increase the pressure of a gas to double its original pressure the volume increases/decreases by what factor?

A) increases, by a factor of 2

B) decreases by a factor of ½

C) increases, by a factor of 4

D) does not change

B) decreases by a factor of ½

200

What happens to the total pressure in a sealed container as this reaction goes to completion?

3 H_{2 (g)} + N_{2 (g)} → 2 NH_{3 (g)}

A) The pressure increases.

B) The pressure decreases.

C) Initially the pressure increases, then it returns to the original pressure.

D) The pressure does not change.

E) Initially the pressure decreases, then it returns to the original pressure.

B) The pressure decreases.

300

Which of the following deviates most from ideal gas behavior?

A) Kr at 1 atm and 800 K

B) Kr at 1 atm and 200 K

C) Kr at STP

D) Kr at 100 atm and 800 K

E) Kr at 100 atm and 200 K

E) Kr at 100 atm and 200 K

400

What is the root mean square speed (m/s) of helium at 20°C?

A) 135.16 m/s

B) 1351.6 m/s

C) 11.164 m/s

D) 353.04 m/s

B) 1351.6 m/s

500

A gas known to have a formula of NO_x was found to effuse at a rate that is 1.033 times the rate of effusion of oxygen gas. What is the value of (x) and what is the molar mass of NO_x ?

A) x = 1, 29.99 g/mol

B) x = 2, 46.01 g/mol

C) x = 3, 62.00 g/mol

A) x = 1, 29.99 g/mol

Mixed Calculations

100

A gaseous mixture contains 2.35 mol He, 2.05 mol Ne, and 2.10 mol Ar. The total pressure of the mixture is 3.45 atm. What is the partial pressure, in atm, of the argon gas?

A) 0.609 atm

B) 1.64 atm

C) 1.25 atm

D) 1.11 atm

E) 1.09 atm

D) 1.11 atm

200

A pure gas sample has a density of 1.54 g/L at 1.12 atm and 300 K. What is its molar mass?

A) 33.8 g/mol

B) 17.9 g/mol

C) 14.3 g/mol

D) 7.01 g/mol

A) 33.8 g/mol

300

Calculate the root mean square velocity of a sample of butane (C₄H₁₀) gas at 487 K. The molecular weight of butane is 58.12 g/mol.

a). 45.4 m/s

b). 523 m/s

c). 14.5 m/s

d). 457 m/s

d). 457 m/s

400

Calculate the initial concentration of HCl solution if 25.00 mL of HCl is titrated with 1.22 M Ca(OH)₂ . The initial buret reading is 1.64 mL and the final buret reading is 32.78 mL.

A) 3.04 M

B) 1.52 M

C) 0.677 M

D) 3.20 M

E) 1.35 M

A) 3.04 M

500

The hydrolysis of diborane (B₂H₆) to give boric acid (B(OH₃)) proceeds according to the following balanced chemical equation:

B₂H_{6 (g)} + 6 H₂O_(l) →  6 H_{2 (g)} + 2 B(OH)_{3 (aq)}

The H₂ generated in this reaction was collected over water using a pneumatic trough. The volume of the collection vessel is 3.75 L and the total pressure inside the vessel after the reaction is complete is 1.67 atm at a temperature of 360.4 K. How much B2H6 was used in the reaction?

The vapor pressure of water at 87.2 °C is 0.617 atm.

Molecular weight of B₂H₆ = 27.67 g/mol

Molecular weight of H₂ = 2.016 g/mol

a). 0.976 g

b). 0.614 g

c). 3.76 g

d). 2.54 g

b). 0.614 g