Chapter 7 Chemical Formulas & Equations What goes in must come out!

Objectives: Determine how to read and understand a balanced chemical equation. Examine some reactions that release energy and others that absorb energy. Explain the Law of Conservation of Mass.

Why It’s Important? Chemical Reactions warm your home, cook your meals, digest your food, and power cars and trucks. Allows chemists to save time in performing a chemical reaction.

Vocabulary : Chemical reaction Reactant Product Chemical equation Endothermic Reaction Exothermic Reaction

Introduction: Balancing a chemical equation is much like the work of an accountant who has to show every penny that comes in and where it has gone to.

Review: Chemical Reaction A process of Chemical Change Write your observations. (Demo)

Energy in Chemical Reactions: Endothermic Reaction: Exothermic Reaction: Reaction in which energy is absorbed Reactants are more stable Reaction in which energy is released. Products are more stable.

Parts of a Chemical Reaction: Reactants Products Substances before the reaction. Substances after the reaction

Define Chemical Equation: Consists of reactants, products, physical state and the number of substances on the reaction. Ex. Vinegar + Baking Soda bubbles + gas

Using Chemical Names: Acetic Acid( vinegar) + Sodium hydrogen carbonate (baking soda) Sodium Acetate + Water + Carbon dioxide (Gas)

Using Chemical Formulas: CH3COOH (acetic acid) + NaHCO3 (Sodium Hydrogen Carbonate) CH3COONA (Sodium Acetate) + H2O (water) + CO2 (carbon dioxide)

Subscripts: Number of atoms of the element Ex. CO2 Carbon-1 Oxygen-2

Coefficient: Number of Molecules

Practice: 4H2O2 4MgCl2 6CaOH2 3NH4 5Al(OH)2 NOTE: #ATOMS = SUBSCRIPT X COEFFICIENT Practice: 4H2O2 4MgCl2 6CaOH2 3NH4 5Al(OH)2

Why Balance a Chemical Equation? Lavoisier, 1788 Because of the principle of the Conservation of Matter, an equation must be balanced. * It must have the same number of atoms of the same kind on both sides.

Law of Conservation of Mass You need to remember this law! The Law of Conservation of Mass states: that mass is neither created nor destroyed in any chemical reaction. * Therefore balancing of equations requires the same number of atoms on both sides of a chemical reaction. The number of atoms in the Reactants must equal the Number of atoms in the Products

Is it Balanced? CH3COOH +NAHCO3 C- H- O- Na- CH3COONa +H20 +CO2 C- H- O- Na-

Steps in Balancing Chemical Equations: Identify the reactants and products. Draw a line to separate R & P. List all the elements. Write the number of atoms and molecules. Check every element in R if balanced with P Balance the Chemical Equation

Try to balance these equations using the same method: 1. CH4 + O2  CO2 + H2O 2. Li + HNO3  LiNO3 + H2 3. Al + O2  Al2O3

How did you get on?? Here are the answers: [1] CH4 + 2 O2  CO2 + 2 H2O [2] 2 Li + 2 HNO3  2 LiNO3 + H2 [3] 4 Al + 3 O2  2 Al2O3

Closure: Reflection: In 2-3 sentences explain why balancing equation is important?