RMS and Graham’s Law
Supplemental Instruction
Iowa State University / Leader: / Kia
Course: / CHEM 177
Instructor: / Dutton
Date: / October 19th, 2017

ACS Final practice

  1. If a 17.0 g sample of impure nickel metal reacts with excess carbon monoxide, CO, forming 6.25 L of Ni(CO)4 gas under standard temperature and pressure conditions, what is the percent by mass of nickel in the impure nickel metal sample? (Molar masses: Ni = 58.7 g/mol and Ni(CO)4 = 171 g/mol)

Ni(s) + 4CO(g)  Ni(CO)4(g)

  1. 24.1%
  2. 25.0%
  3. 96.3%
  4. 100.0%

  1. When 68.00 J of energy are added to a sample of gallium that is initially at 25.0 deg C, the temperature rises to 38.0 deg. C. What is the volume of the sample? (specific heat = 0.372 J/g*deg C, density = 5.904 g/cm^3)

  1. 2.38 cm3
  2. 4.28 cm3
  3. 14.1 cm3
  4. 31.0 cm3

Concept Check

  1. (EOC 6.118) How does the root-mean-square speed of the molecules in a gas vary with molar mass? With temperature?
  1. What does Graham’s law tell us? What can we use this law to determine?
  1. (EOC 6.123) What is the difference between diffusion and effusion?

Practice Problems

  1. (EOC 6.125) Rank the gases SO2, CO2, and NO2 in order of increasing rott-mean-square speed at 0 deg. C
  1. (EOC 6.110) The following reactions were carried out in a cylinder with a piston. If the external pressure is constant, in which reactions will the volume of the cylinder increase? Assume all reactants and products are gases at the same temperature.
  2. CH4(g) + NH3(g)  HCN(g) + 3 H2(g)
  3. H2S(g) + 2O2(g)  H2O(g) + SO3(g)
  4. H2(g) + Cl2(g)  2 HCl(g)
  5. 2 NO2(g)  2 NO(g) + O2(g)
  6. An Odorous gas emitted by a hot spring was found to diffuse 2.92 times slower than helium. What is the molar mass of the emitted gas?
  1. (EOC 6.133) A student measured the relative rate of effusion of carbon dioxide and propane, C3H8, and found that they effuse at exactly the same rate. Did the student make a mistake?
  1. (EOC 6.104) A gas mixture contains 7.0 g of N2, 2.0 g of H2, and 16.0 g of CH4. What is the mole fraction of H2 in the mixture? Calculate the pressure of the gas mixture and the partial pressure of each constituent gas if the mixture is in a 1.00 L vessel at 0 deg. C
  1. (EOC 6.116) A mixture of 0.156 mol of C is reacted with 0.117 mol of O2 in a sealed, 10.0 L vessel at 500 K, producing a mixture of CO and CO2. The total pressure is 0.640 atm. What is the partial pressure of CO?
  1. (EOC 6.178) Several devices are available for generating oxygen. Breathing pure oxygen for any length of time, however, can be dangerous to the human body, so a better rebreathing apparatus would be one that also produces nitrogen. One possible reaction that produces both N2 and O2 is the thermal decomposition of ammonium nitrate:

2 NH4NO2(s)  2 N2(g) + O2(g) + 4 H2O(g)

  1. The respiratory rate at rest for an average, healthy adult is 12 breaths per minute. If the average breath takes in 500 mL of gas into our lungs, what mass in grams of NH4NO3 is needed to satisfy these needs for 1 h if P = 1.00 atm and T = 37 deg. C?
  1. What are the partial pressures of N2 and O2 in the mixture?