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BALANCING CHEMICAL EQUATIONS

BALANCING CHEMICAL EQUATIONS. Recall… Chemical equations summarize chemical reactions methane + oxygen  carbon dioxide + Water CH 4 + O 2  CO 2 + H 2 O. Law of Conservation of Mass. 2H 2 + O 2  2H 2 O 9 girls + 14 boys  10 lab pairs + 1 group of 3

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BALANCING CHEMICAL EQUATIONS

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  1. BALANCING CHEMICAL EQUATIONS • Recall… Chemical equations summarize chemical reactions methane + oxygen  carbon dioxide + Water CH4 + O2 CO2 + H2O

  2. Law of Conservation of Mass 2H2 + O2 2H2O 9 girls + 14 boys  10 lab pairs + 1 group of 3 Both equations have the equal mass on each side of the reaction. **This is because they are BALANCED**

  3. Law of Conservation of Mass steel wool + oxygen  rust 4Fe + 3O2  2Fe2O3 Mass of demo: _____ Mass after demo: _____

  4. Unbalanced Chemical Equations MUST be balanced CH4 + O2 CO2 + H2O REACTANTS: PRODUCTS: C= C= H= H= O= O= 1 4 2 1 2 3

  5. Unbalanced Chemical Equations MUST be balanced CH4 + O2 CO2 + H2O • Write out the Chemical Equation • Balance the equation one element at a time, changing ONLY the COEFFICIENTS! • No chemical formulas change, NO subscripts change, and the number 1 is assumed, NEVER written!

  6. Follow these 5 steps to balance a chemical equations • List and balance metals • List and balance non-metals • List and balance Hydrogens • List and balance Oxygens • Simplify coefficients Remember – Balance H & O last!

  7. We have 4 hydrogen atoms on the left and 2 on the right. By placing the coefficient 2 in front of the water molecule, we will have 4 Hydrogen atoms on both sides. CH4 + O2 CO2 + 2 H2O REACTANTS: PRODUCTS: C= 1C= 1 H= 4H= 2 4 O= 2O= 3 We now have 4 H’s on both sides. Now lets look at Oxygen…are they balanced?

  8. We have 2 Oxygen atoms on the left and now 4 on the right. By placing the coefficient 2 in front of the Oxygen gas molecule, we will have 4 Oxygen atoms on both sides. CH4 + 2O2 CO2 + 2 H2O REACTANTS: PRODUCTS: C= 1C= 1 H= 4H= 2 4 O= 2 4 O= 3 4 Now both sides have an equal number of each atom. THE EQUATION IS BALANCED!!!

  9. What does a balanced equation tell us? • We can learn a lot from a balanced equation. For example, in the last equation: • CH4 + 2O2 CO2 + 2 H2O • Once balanced, we know that each methane molecule (CH4) requires 2 oxygen molecules to react. • Each methane molecule that burns forms 1 molecule of Carbon Dioxide and 2 molecules of water.

  10. Balanced Equations • Balanced chemical equations are the standard way that chemists write about and describe reactions and the amounts involved.

  11. Law of Conservation of Mass steel wool + oxygen  rust 4Fe + 3O2  2Fe2O3 Mass of demo: _____ Mass after demo: _____

  12. Practice Problem • Write the balanced equation that describes burning of magnesium in air to form magnesium oxide. Mg + O2 MgO 1st Metals 2nd Non-metals 3rd Hydrogen 4th Oxygen 5th Simplify

  13. Practice Problem Write the balanced equation that describes burning of magnesium in air to form magnesium oxide. Mg + O2 MgO Reactants: 1 Mg 2 O Products 1 Mg 1 O 1 Mg 1 2 O 1 Mg + O2 2MgO Reactants: 1 Mg 2 O Products 2 Mg 2 O 2 Mg + O2 2MgO Reactants: 2 Mg 2 O Products 2 Mg 2 O

  14. The sum of coefficients on one side will NOT always equal the sum of coefficients on the other side. Why?

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