Chapter 7 Chemical Formulas & Equations

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

2. 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.

3. 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.

4. Vocabulary : • Chemical reaction • Reactant • Product • Chemical equation • Endothermic Reaction • Exothermic Reaction

5. 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.

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

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

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

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

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

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

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

13. Coefficient: • Number of Molecules

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

15. Lavoisier, 1788 Why Balance a Chemical Equation? 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.

16. Law of Conservation of MassYou 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

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

18. 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

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

20. 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

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