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UNIT 10: STOICHIOMETRY. Section 1: What is Stoichiometry?. More than 3000 silk cocoons are needed to make just one kimono. Like silk manufacturers, chemists must know how much reactant they need to make a certain amount of product. Determining the quantities of reactants and products
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Section 1: What is Stoichiometry? • More than 3000 silk cocoons are needed to make just one kimono. Like silk manufacturers, chemists must know how much reactant • they need to make a certain • amount of product. • Determining the quantities • of reactants and products • in a reaction requires a • balanced chemical equation.
Using Balanced Chemical Equations • chemists use balanced chemical equations to calculate how much reactantis neededorproduct is formedin a reaction. • stoichiometry: • the calculation of quantities in chemical reactions.
Interpreting Chemical Equations • A balanced chemical equation can tell the amount of: • atoms, molecules, or moles; • and mass. • The most important info is the ratio of moles of reactants to moles of products, or… • mol-to-mol ratios
Interpreting Chemical Equations • Atoms
Interpreting Chemical Equations • Molecules
Interpreting Chemical Equations • Moles
Interpreting Chemical Equations • Mass & Atoms Mass and atoms are conserved in every chemical reaction
Conceptual Problem 12.1 Atoms Mass Molecules Moles 12 12 164.16 g 164.16 g 5 4 5 4
Mole Ratios A mole ratio is a ratio between the numbers of moles of any two substances in a balanced equation. The number of mole ratios that can be written for any equation is (n)(n – 1) where n is the number of species in the chemical reaction.
Mole Ratios 2Al(s) + 3Br2(l) → 2AlBr3(s) How many mole ratios are there for the above reaction? (n)(n-1) (3)(2) = 6 They are 2 mol Al 3 mol Br2 3 mol Br2 2 mol Al 2 mol Al 2 mol AlBr3 2 mol AlBr3 2 mol Al 3 mol Br2 2 mol AlBr3 2 mol AlBr3 3 mol Br2
Quick Quiz. • 1. What is conserved in the reaction shown below? • H2(g) + Cl2(g) 2HCl(g) • only mass • only mass and atoms • only mass, atoms, and moles • mass, atoms, moles, and molecules
Quick Quiz. • 2. What is the most important information from a chemical equation? • states of matter • moles of products • mol-to-mol ratios of reactants and products • mass of reactants
Quick Quiz. • 3. How many mole ratios can be written for the following reaction? • 4H2(g) + O2(g) → 2H2O(l) • A. 6 • B. 4 • C. 3 • D. 2