Chemistry Puzzle Cache #03 - Stoichiometry Mystery Cache

This cache is a puzzle cache which must be solved using knowledge of chemistry. The cache is co-maintained by the Student Affiliates of the American Chemical Society - Tennessee Tech Chapter.

Stoichiometry is just a big word that means "the ratio of combining of things." We can express the ratios of combining of materials in terms of molecules, moles, or grams, for example.

"Stoichiometry" is derived from the Greek words stoikheion (meaning element) and metron (meaning measure). Stoichiometry rests upon the law of conservation of mass, the law of definite proportions (i.e., the law of constant composition) and the law of multiple proportions. In general, chemical reactions combine in definite ratios of chemicals. Since chemical reactions can neither create nor destroy matter, nor transmute one element into another, the amount of each element must be the same throughout the overall reaction. For example, the amount of element A on the reactant side must equal the amount of element A on the product side.

Stoichiometry is often used to balance chemical equations. For example, the two diatomic gases, hydrogen and oxygen, can combine to form a liquid, water, in an exothermic reaction, as described by the following equation:

The balanced equation represents a complete sentence in English, which can be read in several ways: 1. Two molecules of hydrogen gas combine with one molecule of oxygen gas to form 2 molecules of water, 2. Two moles of hydrogen gas combine with one mole of oxygen gas to form two moles of water, or when converted to mass 3. Four grams of hydrogen gas react with 32 grams of oxygen gas to form 36 grams of water. The mass balances on both sides of the equation, which satisfies the Law of Conservation of Mass.

The term stoichiometry is also often used for the molar proportions of elements in stoichiometric compounds. For example, the stoichiometry of hydrogen and oxygen in H₂O is 2:1. In stoichiometric compounds, the molar proportions are whole numbers (that is what the law of definite proportions is about). Stoichiometry is not only used to balance chemical equations but also used in conversions, i.e., converting from grams to moles, or from grams to milliliters.