Understandings:

Applications & Skills

1.  Reactants can be limiting or excess.
2.  The experimental yield is usually different from the theoretical yield.
3.  Avogadro's law enables the mole ratio of reacting gases to be determined from volumes of the gases.
4.  The molar volume of an ideal gas is a constant at specific temperatures and pressures.

1. Solution of problems relating to reacting quantities, limiting and excess reactants, and theoretical, experimental and percent yields.
2. Calculation of reacting volumes of gases using Avogadro's law.
3. Solution of problems and analysis of graphs involving the relationship between temperature, pressure, and volume for a fixed mass of an ideal gas.
4. Solving ideal gas law problems.

Key Concepts

Theoretical, Experimental & Percent Yield.  The theoretical yield (TY) is the maximum amount of product(s) that can be obtained in a chemical reaction.  It is usually expressed in grams or moles and comes from the chemical equation.  The TY assumes that 100% of the reactants (especially the limiting reactant) is converted to products.  The opposite, of course, is the experimental (or actual) yield.  This is how much the reaction is actually producing, and it is usually less than the TY because of the limiting reactant.

The percent yield measures the efficiency of a reaction.  It is the division of the EY by the TY, multiplied by 100 to get a percentage (obviously).  This is something you'll be asked to calculate regularly.

Source: www.premedhq.com

Mission 1: Gases
Mission Objectives.  You should be able to...
1. Explain the Kinetic Theory of Gases.
2. Describe conditions at STP.
3. Calculation of reacting volumes of gases using Avogadro's law.
4. Solve problems and analyze graphs involving the relationship between temperature, pressure and volume for a fixed mass of an ideal gas.
5. Solve ideal gas law problems.
6. Explain why real gases deviate from ideal behavior at low temperature and high pressure.
7.  Calculate the molar mass of a gas using the ideal gas equation.

Avogadro's Law & The Nature of Gases.  Recall that most of a gas' volume is empty space, so its chemical nature is irrelevant to its volume.  The volume of a gas, therefore, is determined by the number of particles, temperature, and pressure.  So if you have equal volumes of gases measured at the same temperature and pressure, it can be assumed that the equal volumes contain an equal number of particles.  This is Avogadro's Law.  Using Avogadro's Law as basis, the volume occupied by one mole of any gas (the molar volume) must be the same for all gases when measured under the same conditions of temperature and pressure.

To determine the number of moles in a gas, divide the given volume by the molar volume.  It's similar to molar mass calculations.

At Standard Temperature & Pressure (STP), one mole of a gas has a volume of .0227 cubic meters/mole (22.7 decameters/mol).  Standard temperature is 0 degrees Celsius (273 Kelvin) and standard pressure is 100 kpa (1 atm).

The Gas Laws.  These laws describe pressure, volume and temperature relationships for all gases.  The kinetic theory describe gases of negligible volume that have no interparticle forces, thus behaving in an ideal way.

Observations about pressure, volume and temperature of gases having nothing to do with the chemical nature of the gases themselves.  They all respond in the same way to changes in these conditions when the mass of the gas is fixed.

Boyle's Law.  The volume of a gas is inversely proportional to its pressure when temperature remains constant.
Charles' Law.  The volume of a gas is directly proportional to its temperature when pressure remains constant.
Gay Lussac's Law.  The pressure of a gas is directly proportional to its temperature when the volume remains constant.

The Combined Gas Law (CGL) is all three laws rolled into one. They apply to a fixed mass of gas.  Look to the right to see it.  "1" represents initial conditions and "2" represents final conditions.  Using the CGL enables volume, pressure and temperature to be calculated as conditions change.

Think about soft drinks. They're in pressurized cans and come with a warning to be stored in cool, dry places. This is because at higher temperatures, the pressure increases and can cause them to explode.

The Ideal Gas Law is derived from Avogadro's Law and the combined gas law. Look to the left.  "R" is a constant that has different values based on the units that are given in the problem.

R (typically) equals 8.31 J/K*mol or 8.31 N*m/K*mol. This value is given in Section 2 of the Data Booklet.

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​Practice Problems.

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Reacting Masses & Volumes, Part 2.