Conceptual Physics

Section 4 - Avogadro’s number and moles

4.1 How many molecules are there in 0.017 moles of carbon dioxide gas, CO 2?

molecules

4.2 The molar mass of silver is 108 g/mol. What is

the mass in kilograms of the 2.3×10^24 atoms

of silver that make up the chalice in the

illustration?

kg

4.3 The atomic mass of carbon is 12.0 u and of oxygen is 16.0 u, rounded to 3 significant figures. (a) What is the molecular mass
of a carbon dioxide molecule, CO 2 , in atomic mass units? (b) What is the molar mass of carbon dioxide in kg/mol? (c) How
many molecules are in 0.0123 kg of carbon dioxide?
(a) u
(b) kg/mol
(c) molecules

4.4 The molecular mass of water is 18 u. The mass of a teaspoon of water is 4.9×10í^3 kg. If one teaspoon of water were spread

evenly over the surface of the Earth, what would be the surface number density, that is, the number of water molecules per

square meter? (Assume the Earth is a smooth sphere with radius 6.4×10^6 m.)

molecules/m^2

Section 5 - Ideal gas law

5.1 An ideal gas occupies 0.14 m^3 at an absolute pressure of 1.2×10^5 Pa and temperature 280 K. (a) How many moles of gas
are there? (b) How many molecules?
(a) moles
(b) molecules

5.2 At 265 K, the pressure of 0.0453 mol of an ideal gas is 1.42×10^5 Pa. What volume does the gas occupy?

m^3

5.3 A balloon holds 0.0140 m^3 of an ideal gas at a temperature of 35.0°C. If the amount of gas is 0.680 mol, what is the pressure

of the gas?

Pa

5.4 At a pressure of 2.32×10^5 Pa, 6.41×10^25 molecules of an ideal gas occupy 0.752 m^3. What is the temperature of the gas?

K

5.5 A room with dimensions 2.52 × 4.57 × 5.61 m is filled with air at pressure 1.01×10^5 Pa. Air can move into or out of the room

through a crack under the door. The pressure stays constant as the temperature increases from 18.0°C to 24.0°C. What is the

change in the number of moles of air in the room? Treat the air as an ideal gas. (Be careful with the sign of your answer.)

mol

5.6 The atmosphere on Mars is almost all carbon
dioxide (CO 2 ), and has a pressure of about
6.9×10^2 Pa, much less than that of Earth. At
í22°C (a warm day on Mars), what is the
mass of one cubic meter of the atmosphere?
(Assume the atmosphere is completely CO 2 .)

kg

Copyright 2007 Kinetic Books Co. Chapter 19 Problems^371