Name ______Date ______Period _____
Homework
Chapter 10: Gases
Exercises: Sections 10.7, 10.8, 10.9: Kinetic-Molecular Theory; Graham’s Law; Non-Ideal Gas Behavior
1. Indicate which of the following statements regarding kinetic-molecular theory of gases are correct. For those that are false,
formulate a correct version of the statement. Please write either TRUE or FALSE for each
(a) The gas molecules are assumed to exert no forces on each other.
(b) All the molecules of a gas at a given temperature have the same kinetic energy.
(c) The volume of the gas molecules is negligible in comparison to the total volume in which the a gas is contained.
2. Suppose you have two 1-L flasks, one containing N2 at STP, the other containing CH4 at STP. How do these systems compare
with respect to
(a) number of molecules;
(b) density;
(c) average kinetic energy of the molecule;
(d) rate of effusion through a pinhole leak?
3. What is the difference between effusion and diffusion?
4. Grahm's law can be derived from the equation for kinetic energy, EK = ½mv2. See if you can derive Grahm's
law by considering two gases at equal pressure and temperature.
5. Place the following gases in order of increasing average molecular speed at 25oC; CO, SF6, H2S, Cl2, and HI.
6. Calculate the ratio of the effusion rates of N2 and O2, .
7. A gas of unknown molecular mass was allowed to effuse through a small opening under constant pressure conditions. It required
72 s for 1.0 L of the gas to effuse. Under identical experimental conditions it required 28 s for 1.0 L of O2 gas to effuse. Calculate
the molar mass of the unknown gas. (Remember that the faster the rate of effusion, the shorter the time required for effusion of
1.0 L; that is, rate and time are inversely proportional.)
8. Arsenic (III) sulfide sublimes readily, even below its melting point of 320oC. The molecules of the vapor phase are found to
effuse through a tiny hole at 0.28 times the effusion rate of Ar atoms under the same conditions of temperature and pressure. What
is the molecular formula of arsenic(III) sulfide in the gas phase?
9. (a) What is meant by the root mean square (rms) speed of the molecules of a sample of gas?
(b) Calculate the rms, u, speed of CO at 25oC.
7. (a) What causes real gases to have values of PV/ RT that are less than those of an ideal gas?
(b) What causes PV/ RT to be greater for real gases than for an ideal gas?
(c) Why does the difference in PV/ RT values for real gases and ideal gases become smaller as the temperature increases?
8. Briefly explain the significance of the constants a and b in the van der Waals equation.
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