Science, Tech, Math › Science Introduction To Stoichiometry Share Flipboard Email Print Steve McAlister/Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated January 09, 2019 One of the most important parts of chemistry is stoichiometry. Stoichiometry is the study of the quantities of reactants and products in a chemical reaction. The word comes from the Greek words: stoicheion ("element") and metron ("measure"). Sometimes you'll see stoichiometry covered by another name: mass relations. It's a more easily pronounced way of saying the same thing. Stoichiometry Basics Mass relations are based on three important laws. If you keep these laws in mind, you'll be able to make valid predictions and calculations for a chemical reaction. Law of Conservation of Mass - mass of the products equals the mass of the reactantsLaw of Multiple Proportions - the mass of one element combines with a fixed mass of another element in a ratio of whole numbersLaw of Constant Composition - all samples of a given chemical compound have the same elemental composition Common Stoichiometry Concepts and Problems The quantities in stoichiometry problems are expressed in atoms, grams, moles, and units of volume, which means you need to be comfortable with unit conversions and basic math. To work mass-mass relations, you need to know how to write and balance chemical equations. You'll need a calculator and a periodic table. Here's information you need to understand before you start work with stoichiometry: How the Periodic Table WorksWhat a Mole IsUnit Conversions (Worked Examples)Convert Grams To Moles (Step By Step Instructions) A typical problem gives you an equation, asks you to balance it, and to determine the amount of reactant or product under certain conditions. For example, you may be given the following chemical equation: 2 A + 2 B → 3 C and asked, if you have 15 grams of A, how much C can you expect from the reaction if it goes to completion? This would a be a mass-mass question. Other typical problem types are molar ratios, limiting reactant, and theoretical yield calculations. Why Stoichiometry Is Important You can't understand chemistry without grasping the basics of stoichiometry because it helps you predict how much of a reactant participates in a chemical reaction, how much product you'll get, and how much reactant might be left over. Tutorials and Worked Example Problems From here, you can explore specific stoichiometry topics: How To Balance EquationsExample of Balancing an EquationUnderstanding Molar RatiosHow To Find the Limiting ReactantHow To Calculate Theoretical Yield Quiz Yourself Do you think you understand stoichiometry? Test yourself with this quick quiz.