Conceptual Questions

ssm Solution is in the Student Solutions Manual

| 1 | (a) Which, if either, contains a greater number of molecules, a mole of hydrogen (H2) or a mole of oxygen (O2)? (b) Which one has more mass? Give reasons for your answers.

| 2 | Suppose two different substances, A and B, have the same mass densities. (a) In general, does one mole of substance A have the same mass as one mole of substance B? (b) Does 1 m3 of substance A have the same mass as 1 m3 of substance B? Justify each answer.

| 3 | A tightly sealed house has a large ceiling fan that blows air out of the house and into the attic. This fan is turned on, and the owners forget to open any windows or doors. What happens to the air pressure in the house after the fan has been on for a while, and does it become easier or harder for the fan to do its job? Explain.

| 4 | ssm Above the liquid in a can of hair spray is a gas at a relatively high pressure. The label on the can includes the warning “Do not store at high temperatures.”Use the ideal gas law and explain why the warning is given.

| 5 | Assuming that air behaves like an ideal gas, explain what happens to the pressure in a tightly sealed house when the electric furnace turns on for a while.

| 6 | When you climb a mountain, your eardrums “pop” outward as the air pressure decreases. When you come down, they pop inward as the pressure increases. At the sea coast, there is a cave that can be entered only by swimming through a completely submerged passage and emerging into a pocket of air within the cave. The cave is not vented to the external atmosphere. As the tide comes in, the water level in the cave rises, and your eardrums pop. Is this popping analogous to what happens as you climb up or down a mountain? Give your reasoning.

| 7 | Atmospheric pressure decreases with increasing altitude. With this fact in mind, explain why helium-filled weather balloons are underinflated when they are launched from earth.

| 8 | A slippery cork is being pressed into a very full (but not 100% full) bottle of wine. When released, the cork slowly slides back out. However, if some wine is removed from the bottle before the cork is inserted, the cork does not slide out. Account for these observations in terms of the ideal gas law.

| 9 | A commonly used packing material consists of “bubbles”of air trapped between bonded layers of plastic, as the photograph shows. Using the ideal gas law, explain why this packing material offers less protection on cold days than on warm days.

(The Photo Works)

| 10 | ssm The kinetic theory of gases assumes that a gas molecule rebounds with the same speed after colliding with the wall of a container. Suppose the speed after the collision is less than that before the collision. Would the pressure of the gas be greater than, equal to, or less than that predicted by kinetic theory? Account for your answer.

| 11 | If the translational speed of each molecule in an ideal gas were tripled, would the Kelvin temperature also triple? If not, by what factor would the Kelvin temperature increase? Account for your answer.

| 12 | If the temperature of an ideal gas is doubled from 50 to 100 °C, does the average translational kinetic energy of each particle double? If not, why not?

| 13 | It is possible for both the pressure and volume of a monatomic ideal gas to change without causing the internal energy of the gas to change. Explain how this could occur.

| 14 | ssm Suppose that the atoms in a container of helium (He) have the same translational rms speed as the molecules in a container of argon (Ar). Treating each gas as an ideal gas, explain which, if either, has the greater temperature.

| 15 | The ionosphere is the uppermost part of the earth’s atmosphere. The temperature of the ionized gas in the ionosphere is about 1000 K. However, the density of the gas is extremely low, on the order of 1011 molecules/m3. Although the temperature is very high, an astronaut in the ionosphere would not burn up. Why?

| 16 | In the lungs, oxygen in very small sacs called alveoli diffuses into the blood. The diffusion occurs directly through the walls of the sacs. The walls are very thin, so the oxygen diffuses over a distance L that is quite small. Because there are so many alveoli, the effective area A across which diffusion occurs is very large. Use this information, together with Fick’s law of diffusion, to explain why the mass of oxygen per second that diffuses into the blood is large.

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