You will solve stoichiometric problems of gases by using volume ratios and the ideal gas law.
After completing this tutorial, you will be able to complete the following:
How do you measure something you can't see? How do you make sure there is enough reactant material to produce the desired quantity of product? Stoichiometry is the branch of chemistry that provides answers to these and similar questions about mass and volume. It is the study of the quantitative relationships that exist in chemical formulas and chemical reactions. It is especially important to the study of gases, as they may be odorless, colorless, and formless.
Stoichiometry was first used by chemists in the 1700s. Although the idea of a balanced equation has not changed, calculations are now based on modern ideas about the atom. Especially important in gas stoichiometry is the concept of a mole, a dimensionless number of particles of an element. The mole is a constant number for gases in the same pressure and temperature. The mole has a convenient relationship in chemical equations, known as the volume ratio.
One mole of a product will contain the number of moles of its reactants. For example, one mole of ammonia (NH3) contains one mole of nitrogen and three moles of hydrogen. The volume ratio also relates to all quantities of all materials in a balanced equation. The equation to produce NH3 from nitrogen and hydrogen is According to the volume ratio, 1 mole of N in this reaction will produce 2 moles of . And, if you have 2 moles of nitrogen and want to know how much ammonia will be produced at standard temperature and pressure (1atm, 273K), use the ideal gas law (pV = nRT) to find the answer. In this case, the equation would be:
This activity highlights a three-step process to solve stoichiometry problems. In the first step, students learn to identify the information given in the problem, and the information they must find. In the second step, they identify the calculations they must carry out, and plan their sequence. In the final step, students carry out calculations to find the solution.
|Approximate Time||20 Minutes|
|Pre-requisite Concepts||Learners should be able to define the concept of mole and molar mass in terms of atomic mass, as well as define Avogadros number. Students should also be familiar with problem solving, the ideal gas law, and the concept of standard temperature and pressure (STP).|
|Type of Tutorial||Problem Solving|
|Key Vocabulary||gases, mass, mole|