Chapter 12 Stoichiometry Ch The Arithmetic of Equations

Using Everyday Equations When baking cookies, the recipe tells how much of each ingredient to mix to make a certain number of cookies. When baking cookies, the recipe tells how much of each ingredient to mix to make a certain number of cookies. A balanced chemical equation provides the same kind of quantitative information that a recipe does. A balanced chemical equation provides the same kind of quantitative information that a recipe does. Analogy of cookies: ingredients=reactants cookies=products Analogy of cookies: ingredients=reactants cookies=products

Using Balanced Chemical Equations Chemists use balanced chemical equations as a basis to calculate how much reactant is needed or product is formed in a reaction. Chemists use balanced chemical equations as a basis to calculate how much reactant is needed or product is formed in a reaction. If you know the quantity of one substance in a reaction, you can calculate the quantity of any other substance consumed or created in the reaction. If you know the quantity of one substance in a reaction, you can calculate the quantity of any other substance consumed or created in the reaction. This subject is called stoichiometry. This subject is called stoichiometry.

Interpreting Chemical Equations A balanced chemical equation can be interpreted in terms of different quantities, including number of atoms, molecules, or moles; mass; and volume. A balanced chemical equation can be interpreted in terms of different quantities, including number of atoms, molecules, or moles; mass; and volume. Number of atoms—a balanced equation has the same number and type of atoms in both the reactants and the products. Number of atoms—a balanced equation has the same number and type of atoms in both the reactants and the products. Number of molecules—may be different on each side of a balanced reaction. Number of molecules—may be different on each side of a balanced reaction.

Number of moles—may be different on each side of a balanced reaction. Number of moles—may be different on each side of a balanced reaction. Mass—the law of conservation of mass requires that the total mass of atoms in a reaction does not change. Total grams reactants=total grams products. Mass—the law of conservation of mass requires that the total mass of atoms in a reaction does not change. Total grams reactants=total grams products. Volume—assuming STP, one mole always equals 22.4L. Volume—assuming STP, one mole always equals 22.4L. STP—0° Celsius equals 273° Kelvin (K) STP—0° Celsius equals 273° Kelvin (K)

Mass Conservation in Chemical Reaction MASS AND ATOMS ARE CONSERVED IN EVERY CHEMICAL REACTION. MASS AND ATOMS ARE CONSERVED IN EVERY CHEMICAL REACTION.