Writing chemical Reactions Use a Periodic Table to determine what each of these symbols stand for: Record the symbol and what it stands for. Au Pb Ag Sn You can find free printable Periodic Tables for your class here: http://chemistry.about.com/od/periodictableelements/a/printperiodic.htm Fe Al Ca C (c) S. Coates 2012

Writing chemical Reactions Au Pb Ag Sn Gold Lead Silver Tin Fe Al Ca C Iron Calcium Carbon Aluminum (c) S. Coates 2012

Writing chemical Reactions There are TWO hydrogen atoms You have already seen many chemical formulas… H2O What does the “H” stand for? What does the “O” stand for? What does the little “2” stand for? Hydrogen *This information should be added to the graphic organizer Oxygen There are TWO hydrogen atoms (c) S. Coates 2012

Compound Formula Aspirin C9H8O4 Bleach NaClO Sugar C12H22O11 Rust Here are some familiar items. Use a Periodic Table of the Elements to record what these compounds are made of… Compound Formula Aspirin C9H8O4 Bleach NaClO Sugar C12H22O11 Rust Fe2O3 Rubbing Alcohol C3H8O Lowercase “L”, not an I. (c) S. Coates 2012

Understanding Written Equations Writing chemical Reactions Compound Formula Made of…. Aspirin C9H8O4 9 Carbons, 8 Hydrogens, and 4 Oxygens Bleach NaClO 1 Sodium, 1 Chlorine, 1 Oxygen Sugar C12H22O11 12 Carbons, 22 Hydrogens, and 11 Oxygens Rust Fe2O3 2 Irons, 3 Oxygens Rubbing Alcohol C3H8O 3 Carbons, 8 Hydrogens, and 1 Oxygen (c) S. Coates 2012

Writing chemical Reactions Structure of a chemical equation: Every chemical equation is written THE SAME WAY… Reactant + Reactant  Product + Product Sometimes there are more than 2 reactants. Sometimes there is only 1 reactant. Sometimes there are more than 2 products. Sometimes there is only 1 product. (c) S. Coates 2012

Writing chemical Reactions See if you can answer the following questions for this chemical reaction: CaCO3 CaO + CO2 (Heated) How many reactants are there? What is/are the reactant(s)? How many products are there? What is/are the product(s)? (c) S. Coates 2012

Writing chemical Reactions CaCO3 CaO + CO2 * Notice that the atoms we began with are the same atoms we end with, just in a different order! (Heated) Ca C O O O 3 2 (c) S. Coates 2012

Understanding chemical Reactions The amount of matter involved in a chemical reaction does not change. The total mass of the reactants MUST EQUAL the total mass of the products. We call this principle Conservation of Mass. (c) S. Coates 2012

Writing chemical Reactions How do you know if the mass of the products is equal to the mass of the reactants? Subscript Numbers! If you add up the NUMBER of EACH element on the reactant side and compare it to the NUMBER of the SAME element on the product side you can tell if the mass of the reactants is equal to the mass of the products. CaCO3  CaO + CO2 (c) S. Coates 2012

Understanding chemical Reactions Yes! The masses are equal! For example: Na + Cl  NaCl 1. Count up the number of Na and Cl atoms on the reactant side. Na = 1 Cl = 1 2. Count up the number of Na and Cl atoms on the product side. 3. Compare the numbers. Are they the same? If so then the mass of the reactants and the products is equal. Yes! The masses are equal! (c) S. Coates 2012

Understanding chemical Reactions Here’s another: Fe2 + S2  Fe2S2 1. Count up the number of Fe and S atoms on the reactant side. Fe = 2 S = 2 2. Count up the number of Fe and S atoms on the product side. 3. Compare the numbers. Are they the same? If so then the mass of the reactants and the products is equal. Yes! The masses are equal! (c) S. Coates 2012

Understanding chemical Reactions That makes this equation “unbalanced” But what if the numbers are NOT equal? H2 + O2  H2O 1. Count up the number of H and O atoms on the reactant side. H = 2 O = 2 2. Count up the number of H and O atoms on the product side. H = 2 O = 1 3. Compare the numbers. Are they the same? NO! The masses are NOT equal! That makes this equation “unbalanced” (c) S. Coates 2012

Understanding chemical Reactions That makes this equation “unbalanced” Try another one… CO2 + H2O  C6H12O6 + O2 1. Count up the number of C, H, and O atoms on the reactant side. C = 1 H = 2 O = 3 2. Count up the number of H and O atoms on the product side. C = 6 H = 12 O = 8 3. Compare the numbers. Are they the same? NO! The masses are NOT equal! That makes this equation “unbalanced” (c) S. Coates 2012

Understanding chemical Reactions What do you do when an equation is “unbalanced?” That’s something you’ll be learning in high school Chemistry. For now you just need to understand whether and equation is balanced or unbalanced. (c) S. Coates 2012

Understanding chemical Reactions Let’s summarize: Chemical reactions can cause changes in properties and changes in energy. Chemical reactions occur when the bonds between atoms break, or when new bonds between atoms are formed. We can write equations for chemical reactions by using symbols Chemical reactions must follow the Law of Conservation of Mass. (c) S. Coates 2012