Stoichiometry We are going to be looking at Stoichiometry in this unit, as well as the Mole and mole calculations for solids, liquids, and gases. • Stoichiometry is a section of chemistry that involves using relationships that exist between reactants and/or products in a chemical reaction to determine desired quantitative data. • In Greek, stoikhein means element and metron means measure, so stoichiometry literally translated means the measure of elements. • In order to use stoichiometry to run calculations about chemical reactions, it is important to first understand the relationships that exist between products and reactants and why they exist, which require understanding how to balanced reactions. • Think of chemical reactions, or equations, as being like recipes – we add things (reactants) together to get the finished product. • This is why you learned about balancing equations last week. The coefficients used to balance equations are called stoichiometric coefficients. • They tell us the ratios that apply to the reactants and the products. • Almost any quantitative relationship can be converted into a stoichiometric ratio – as we will see. Moles • This is a mole • Just kidding – this is not the Mole we are going to be discussing in this course. • The Mole we use in Chemistry is a unit of measurement and is defined as the amount of any substance that contains as many elementary entities (e.g. atoms, molecules, electrons, and ions) as there are in exactly 12 grams of pure Carbon-12 (the isotope of Carbon with the relative atomic mass of 12). • This corresponds to Avogadro’s number, which has the value of 6.023 x 1023. • The mole is a base unit of the SI system and has a unit symbol mol Some history • Amedeo Avogadro was an Italian scientist who, in 1811, first proposed that the volume of a gas (at a given temperature and pressure) is proportional to the number of atoms or molecules of that gas. • Jean Perrin, a French physicist, proposed in 1909 the constant should be named in honour of Avogadro. Perrin won the Nobel Prize in Physics in 1926 for his work in determined the Avogadro constant by several different methods. • Accurate determinations of Avogadro's number require the measurement of a single quantity on both the atomic and macroscopic scales using the same unit of measurement. • This became possible for the first time when American physicist Robert Millikan measured the charge of an electron in 1910. • The electric charge per mole of electrons is a constant called the Faraday constant when, in 1834, Robert Faraday published his work on electrolysis. • By dividing the charge of a mole of electrons by the charge of a single electron the value of Avogadro’s number is obtained. • Avogadro’s number is the center core of Chemistry – much like Evolution is the central tenet of Biology. How big is 6.023x1023??? • • • • You have a single little smartie. It doesn’t look like much, does it? Now take 6.023x1023 of the little buggers. How much room would a mole of smarties occupy? • If you could count 10 every second, how long would it take to count them all? MOLE CALCULATIONS FOR SOLIDS