Stoichiometry of Gaseous Substances, Mixtures, and Reactions Quiz

PDF page 491: nRT n RT The ratio m/n is the definition of molar mass, M: m M = n The density equation can then be written MP d = RT This relation may be used for calculating the densities of gases of known identities at specified values of pressure and temperature as demonstrated in Example 9.11.

PDF page 491: What is the density of molecular nitrogen gas at STP? Solution The molar mass of molecular nitrogen, N2, is 28.01 g/mol. Substituting this value along with standard temperature and pressure into the gas density equation yields (28.01 g/mol)(1.00 atm) MP d = = = 1.25 g/L −1 −1 RT (0.0821 L·atm·mol K )(273 K) Check Your Learning What is the density of molecular hydrogen gas at 17.0 °C and a pressure of 760 torr? Answer: d = 0.0847 g/L

PDF page 492: mRT M = PV Determining the molar mass of a gas via this approach is demonstrated in Example 9.12.

PDF page 491: When the identity of a gas is unknown, measurements of the mass, pressure, volume, and temperature of a sample can be used to calculate the molar mass of the gas (a useful property for identification purposes). Combining the ideal gas equation PV = nRT and the definition of molarity m M = n yields the following equation:

PDF page 492: M = = = 42.0 g/mol PV (0.984 atm)(1.00 L) Comparing the molar mass to the empirical formula mass shows how many empirical formula units make up a molecule: M 42.0 g/mol = = 3 EM 14.0 g/mol The molecular formula is thus derived from the empirical formula by multiplying each of its subscripts by three: (CH ) = C H 2 3 3 6

PDF page 492: Check Your Learning Acetylene, a fuel used welding torches, is composed of 92.3% C and 7.7% H by mass. Find the empirical formula. If 1.10 g of acetylene occupies of volume of 1.00 L at 1.15 atm and 59.5 °C, what is the molecular formula for acetylene? Answer: Empirical formula, CH; Molecular formula, C2H2

PDF page 493: mRT M = = = 120 g/mol. PV 0.976 atm × 0.129 L Check Your Learning

PDF page 493: A sample of phosphorus that weighs 3.243 × 10 g exerts a pressure of 31.89 kPa in a 56.0-mL bulb at 550 °C. What are the molar mass and molecular formula of phosphorus vapor? Answer: 124 g/mol P4

PDF page 493: Unless they chemically react with each other, the individual gases in a mixture of gases do not affect each other’s pressure. Each individual gas in a mixture exerts the same pressure that it would exert if it were present alone in the container (Figure 9.20). The pressure exerted by each individual gas in a mixture is called its partial pressure. This observation is summarized by Dalton’s law of partial pressures: The total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of the component gases: P

PDF page 493: Unless they chemically react with each other, the individual gases in a mixture of gases do not affect each other’s pressure. Each individual gas in a mixture exerts the same pressure that it would exert if it were present alone in the container (Figure 9.20). The pressure exerted by each individual gas in a mixture is called its partial pressure. This observation is summarized by Dalton’s law of partial pressures: The total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of the component gases: P

PDF page 494: The partial pressure of gas A is related to the total pressure of the gas mixture via its mole fraction (X), a unit of concentration defined as the number of moles of a component of a solution divided by the total number of moles of all components: n A X =

PDF page 495: A n Total For O2, n O 2.83 mol 2 X = = = 0.252 O n 2 (2.83 + 8.41) mol Total

PDF page 495: = 0.748 × 192 kPa = 143.6 kPa