Q: What is the average kinetic energy per mole of O$$_2 at 25$^ ext{o}C$$?

$$3.72 \times 10^3$\ \mathrm{J/mol}$$

Question 1

A sample of CO$$_2$$ gas was found to effuse through a pinhole at a rate of 0.033 mol/min. Using the same setup, 0.033 mol of a mystery gas effused in 104 seconds. What is the molar mass of the mystery gas?

Accepted Answer

$$60.0\ \mathrm{g/mol}$$

Question 2

If the mystery gas in the previous question is monoatomic, which of the following elements is most likely the identity of the gas?

Accepted Answer

Krypton (Kr)

Question 3

A 6.00 L tank contains 350 g of H$$_2O $$gas at a temperature of 566 K. What is the pressure in the tank (in bar) assuming H$$_2O $$behaves ideally?

Accepted Answer

$$22.5\ \mathrm{bar}$$

Question 4

When calculating the pressure of H$$_2O $$gas in a tank using the van der Waals equation, which factor causes the pressure to be lower than the ideal gas prediction?

Accepted Answer

Intermolecular attractions between H$$_2O $$molecules

Question 5

A 1.0 L flask contains 1.00 g of O$$_2 at 25$^	ext{o}C. $$What is the root mean square speed ($$u_{rms}) of O$_2$$ molecules?

Accepted Answer

$$482\ \mathrm{m/s}$$

Question 6

What is the average kinetic energy per mole of O$$_2 at 25$^	ext{o}C$$?

Accepted Answer

$$3.72 	imes 10^3$\ \mathrm{J/mol}$$

Question 7

A mountain climber has partial pressures of O$$_2$$ and CO$$_2 in $$her lungs of 4.7 kPa and 1.0 kPa, respectively. The atmospheric pressure on the mountain is 33.7 kPa. Assuming the lungs are saturated with water vapor at a temperature of 310 K (vapor pressure of water at this temperature is 6.3 kPa), what is the partial pressure of N$$_2 in $$her lungs?

Accepted Answer

$$21.7\ \mathrm{kPa}$$

Question 8

Assuming the volume of the climber's lungs is 6.0 L, how many molecules of O$$_2$$ are in her lungs?

Accepted Answer

$$6.59 	imes 10$$^{22}$$

Question 9

A 3.00 L flask contains 0.078 g of a gas with molecular formula SO$$_x. $$The temperature is 22$$^	ext{o}C $$and the pressure is 1.00 bar. Is the unknown gas SO$$_2 or SO$_3$$?

Accepted Answer

SO$$_2$$

Question 10

Calculate the enthalpy change ($$\Delta H) $$for the reaction: $$\mathrm{Mg(OH)_2 (s) + 2 H_2O (l) \rightarrow Mg$$^{2+}$$ (aq) + 2 OH^- (aq)}$$ using the following enthalpies of formation: $$\Delta H_f (Mg(OH$$)$$_2$$) = $$-924.54\ \mathrm{kJ/mol}$$, $$\Delta H_f (H$_2O$$) = $$-285.83\ \mathrm{kJ/mol}.$$

Accepted Answer

$$+280.4\ \mathrm{kJ/mol}$$

Question 11

In a particular flameless heater, 425 mL of water at 25.4$$^	ext{o}C is $$added to a pouch containing 4.25 g of Mg. What will be the final temperature of the resulting solution? (Assume $$c_{water} = 4.184\ \mathrm{J\ g$$^{-1}$$\ ^	ext{o}C$$^{-1}$$}$$, density of water = $$1.00\ \mathrm{g/mL}$$, and $$c_{aluminum} = 0.903\ \mathrm{J\ g$$^{-1}$$\ ^	ext{o}C$$^{-1}$$}.)$$

Accepted Answer

$$60.1\ ^	ext{o}C$$

Question 12

Aerobic respiration can be regarded as the complete combustion of glucose. Calculate the enthalpy of glucose combustion using the reaction: $$\mathrm{C_6H_{12}O_6$ (s) + 6 O_2$ (g) \rightarrow 6 CO_2$ (g) + 6 H_2O (l)}$$ and the following enthalpies of formation: $$\Delta H_f (CO$_2$$) = $$-393.5\ \mathrm{kJ/mol}$$, $$\Delta H_f (H$_2O$$) = $$-285.8\ \mathrm{kJ/mol}$$, $$\Delta H_f (C$_6H$_{12}O$_6$$) = $$-1271.0\ \mathrm{kJ/mol}.$$

Accepted Answer

$$-2804.8\ \mathrm{kJ/mol}$$

Question 13

Calculate the change in internal energy ($$\Delta U) $$for the reaction at 1.00 bar and 298 K: $$\mathrm{C_8H_{18}(l) + \frac{17}{2} O_2$ (g) \rightarrow 8 CO_2$ (g) + 9 H_2O (l)}$$, given $$\Delta H = -5430\ \mathrm{kJ/mol}.$$

Accepted Answer

$$-5370\ \mathrm{kJ/mol}$$

Question 14

A cylinder filled with gas with a moveable piston on top is allowed to move up if the gas in the cylinder expands and moves down when the gas contracts. If the initial volume of gas in the cylinder is 45.0 mL and the final volume is 24.5 mL, what is the work done by the system against a constant external pressure of 0.727 bar?

Accepted Answer

$$-1.49\ \mathrm{J}$$

Question 15

Which of the following statements best explains why the pressure calculated using the van der Waals equation for H$$_2O is $$lower than the pressure calculated using the ideal gas law?

Accepted Answer

The van der Waals equation accounts for the attractive forces between H$$_2O $$molecules, which reduces the pressure.

Question 16

Which of the following gases would have the highest root mean square speed ($$u_{rms}) at 25$^	ext{o}C$$?

Accepted Answer

He

Question 17

A reaction takes place inside a gas cylinder, which results in $$w = -245\ \mathrm{J}$$ and $$q = 0\ \mathrm{J} ($$both with respect to the system). What is the change in internal energy ($$\Delta U) $$for the system?

Accepted Answer

$$-245\ \mathrm{J}$$

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