# 13.E: Solids, Liquids, and Gases (Exercises)

1. How many grams of oxygen gas are needed to fill a 25.0 L container at 0.966 atm and 22°C?

2. A breath of air is about 1.00 L in volume. If the pressure is 1.00 atm and the temperature is 37°C, what mass of air is contained in each breath? Use an average molar mass of 28.8 g/mol for air.

3. The balanced chemical equation for the combustion of propane is as follows:

$C_3H_{8(g)} + 5O_{2(g)} \rightarrow 3CO_{2(g)} + 4H_2O_{(ℓ)}$

1. If 100.0 g of propane are combusted, how many moles of oxygen gas are necessary for the reaction to occur?
2. At STP, how many liters of oxygen gas would that be?
4. The equation for the formation of ammonia gas (NH3) is as follows:

$N_{2(g)} + 3H_{2(g)} \rightarrow 2NH_{3(g)}$

At 500°C and 1.00 atm, 10.0 L of N2 gas are reacted to make ammonia.

1. If the pressures and temperatures of H2 and NH3 were the same as those of N2, what volume of H2 would be needed to react with N2, and what volume of NH3 gas would be produced?
2. Compare your answers to the balanced chemical equation. Can you devise a “shortcut” method to answer Exercise 4a?
5. At 20°C, 1 g of liquid H2O has a volume of 1.002 mL. What volume will 1 g of water vapor occupy at 20°C if its pressure is 17.54 mmHg? By what factor has the water expanded in going from the liquid phase to the gas phase?

6. At 100°C, 1 g of liquid H2O has a volume of 1.043 mL. What volume will 1 g of steam occupy at 100°C if its pressure is 760.0 mmHg? By what factor has the water expanded in going from the liquid phase to the gas phase?

7. Predict whether NaCl or NaI will have the higher melting point. Explain. (Hint: consider the relative strengths of the intermolecular interactions of the two compounds.)

8. Predict whether CH4 or CH3OH will have the lower boiling point. Explain. (Hint: consider the relative strengths of the intermolecular interactions of the two compounds.)

9. A standard automobile tire has a volume of about 3.2 ft3 (where 1 ft3 equals 28.32 L). Tires are typically inflated to an absolute pressure of 45.0 pounds per square inch (psi), where 1 atm equals 14.7 psi. Using this information with the ideal gas law, determine the number of moles of air needed to fill a tire if the air temperature is 18.0°C.

10. Another gas law, Amontons’s law, relates pressure and temperature under conditions of constant amount and volume:

$$\mathrm{\dfrac{P_i}{T_i}=\dfrac{P_f}{T_f}}$$

If an automobile tire (see Exercise 9) is inflated to 45.0 psi at 18.0°C, what will be its pressure if the operating temperature (i.e., the temperature the tire reaches when the automobile is on the road) is 45.0°C? Assume that the volume and the amount of the gas remain constant.

1. 31.9 g

2. 1.13 g

3.

1. 11.4 mol
2. 255 L
4.
a. 30.0 L H2 and 20.0 L NH3
b. the mole ratio in the balanced equation is the same as the volume ratio.
$$\mathrm{10.0\: L\: N_2\times\dfrac{3\: L\ H_2}{1\: L\ N_2}=30.0\: L\ H_2}$$
$$\mathrm{10.0\: L\: N_2\times\dfrac{2\: L\ NH_3}{1\: L\ N_2}=20.0\: L\ NH_3}$$
1. 57.75 L; an expansion of 57,600 times

6. 1.698 L; an expansion of 1,628 times
1. NaCl; with smaller anions, NaCl likely experiences stronger ionic bonding.

8. CH4 will have the lower boiling point because its intermolecular force (London dispersion force only) is weaker than those in CH3OH. Aside from London dispersion, CH3OH has dipole-dipole and hydrogen bonding.

9. 11.6 mol

10. 49.2 psi