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# Balancing equations

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• ### Balancing equations

1. 1. • Chemical reactions result in chemical changes. – Chemical changes occur when new substances are created. – The original substance(s), called reactants, change into new substance(s) called products. (c) McGraw Hill Ryerson 2007 See pages 202 - 203
2. 2. (c) McGraw Hill Ryerson 2007 See pages 202 - 203
3. 3. • Chemical reactions can be written in different ways. – A word equation: • Nitrogen monoxide + oxygen → nitrogen dioxide – A symbolic equation: • 2NO(g) + O2(g) → 2NO2(g) COEFFICIENTS STATE OF MATTER - Letters indicate the state of each compound. (aq) = aqueous/dissolved in water - Indicates how many of each molecule there is. (s) = solid -Ie: there are 2 molecules of NO. (g) = gas (c) McGraw Hill Ryerson 2007 ( ) = liquid
4. 4. • When a chemical reaction occurs, new compounds are created, BUT… – No new matter is created or destroyed; atoms are destroyed just rearranged as the atoms change partners to form new compounds. – If there are 3 atoms of oxygen in the reactants, there MUST be 3 atoms of oxygen in the products. – Number of each atom in reactants = number of each atom in products. • The law of conservation of mass: – Mass of reactants = mass of products If you could collect and measure all of the exhaust from this car, you would find that mass of reactants (gas + O2) = mass of products (exhaust). (c) McGraw Hill Ryerson 2007
5. 5. • A balanced chemical equation shows all atoms and the coefficients tells us how many molecules (and atoms) there are. – Balancing ensures that the number of each atom is the same on both sides of the reaction arrow. 4K K K K K + O2 O O → 2K2O K O K K O K
6. 6. Skeleton equation: The same number of atoms must be on each side. Balanced equation: CH4 + O2 → H2O + CO2 Carbon = 1 Hydrogen = 4 Oxygen = 2 Carbon = 1 Hydrogen = 2 Oxygen = 3 CH4 + 2O2 → 2H2O + CO2 Carbon = 1 Hydrogen = 4 Oxygen = 4 (c) McGraw Hill Ryerson 2007 Carbon = 1 Hydrogen = 4 Oxygen = 4 See Page 207
7. 7. Balancing Equations hydrogen + oxygen H2 + H O O2   water H2O Reactants 2 Products 2 2 1
8. 8. Balancing Equations + oxygen  hydrogen peroxide X hydrogen H2 + O2  H2O2 YOU CANNOT CHANGE THE SUBSCRIPTS H O Reactants 2 2 Products 2 2
9. 9. Balancing Equations hydrogen + oxygen H2 + H O O2 Reactants 2 2  water  2H2O Products 2 1
10. 10. Balancing Equations hydrogen + oxygen H2 + H O O2 Reactants 2 2  water  2H2O Products 4 2
11. 11. Balancing Equations hydrogen + oxygen 2 H(g) + 2 H O O2 Reactants 4 2 (g)  water  2H2O (l) Products 4 2
12. 12. http://www.authorstream.com/Presentation/kellymdeters-86103-section-2-7-balancin
13. 13. • Balance the following: – ____Fe + ____Br2 → _____FeBr3 Sn(NO2)4 + C2H6 + K3PO4 → O2 → KNO2 + CO2 + H2O Sn3 (PO4)4
14. 14. ____Ba + ____H2O ____CO2 + ____H2O → → ____Ba(OH)2 + ____H2 ____H2CO3 ____Fe2O3 + ____C → ____Fe + ____CO ____Fe + ____H2O → ____H2 + ____Fe2O3