Gases and Stoichiometry Law of Combining Volumes of

Gases and Stoichiometry

Law of Combining Volumes of reactants and products in gaseous form exist in whole-number ratios Gases must be at SAME temperature and pressure Applies for reactions not carried out at a specific temperature or pressure Can be applied to gases existing with other compounds present in the liquid or solid state

Example 1 2 H 2(g) + O 2(g) 2 H 2 O(g) Combined volume/mole ratio---2: 1: 2

At Standard Temperature and Pressure (0°C, 1 atm) 1 mole gas = 22. 4 L

Example 1: 0. 556 L of propane gas (C 3 H 8) is burned. What volume of oxygen gas is needed if both gas volumes were determined at the same temperature and pressure?

Ideal Gas Law and Stoichiometry If gases are NOT at STP, Use mole ratios and ideal gas law

Example 2: Quicklime (Ca. O) is used in construction. This compound is produced by the decomposition of limestone (Ca. CO 3). When 45. 8 kg Ca. CO 3(s) are decomposed, how many liters of CO 2 gas is produced at 825°C and 754 Torr?

Diffusion with Gases Gas molecules are able to spread through an area until an even distribution of molecules is achieved Molecular collisions hinder the diffusion rate Relatively slow---molecules more 100’s of meters per second

Effusion Passage of gas through a small opening into a vacuum. Lighter molecules travel faster than heavier molecules Effusion rate— Measurement of how fast gas passes through an opening

Graham’s Law of Effusion rate of gas molecules is INDIRECTLY proportional to the square root of the molar masses of these molecules. Effusion time is proportional to 1/effusion rate Rate of gas 1 = √M 2 Rate of gas 2 = √M 1

Example 3: Which gas effuses faster, N 2 or Ar, when the two gases are compared under the same conditions? How much faster?

Example 4: Under the same conditions, how much faster does hydrogen effuse than helium through a small hole?

Gas Equilibrium Worksheet