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Conservation of Mass and Chemical Equations

Conservation of Mass and Chemical Equations. Mr. MacMillan. Chemical reaction One or more chemical changes that occur at the same time. Involves the reaction of a substance to produce a new substance. A chemical change always involves reactants and products Reactants

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Conservation of Mass and Chemical Equations

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  1. Conservation of Mass and Chemical Equations Mr. MacMillan

  2. Chemical reaction • One or more chemical changes that occur at the same time. • Involves the reaction of a substance to produce a new substance

  3. A chemical change always involves reactants and products • Reactants • A pure substance that undergoes a chemical change • Products • A pure substance formed in a chemical change; the properties of the product are different from the properties of the reactant.

  4. The Law of Conservation of Mass • In a chemical reaction, the total mass of the products is always the same as the total mass of the reactants.

  5. Writing Chemical Equations • Chemical equation • A representation of what happens to the reactants and products during a chemical change • Word equations Hydrogen + Oxygen  Water • Skeleton equations H2 + O2  H2O • Balanced chemical equations 2H2 + O2 2H2O

  6. Balancing chemical equations • How to Balance Chemical Equations: • H2 + O2  H2OIn the skeleton equation, there is the same number of hydrogen atoms on both sides of the equation. There are more Oxygen atoms in the reactants, however, than in the product. • H2 + O2  2H2OPlacing the coefficient 2 in front of H2O causes the number of Oxygen atoms on both sides of the equation to be the same. Since the coefficient applies to all the elements in the compound, it causes the number of Hydrogen atoms in the product to increase (to 4) • 2H2+ O2  2H2OPlacing the coefficient 2 in front of H2 makes the number of Hydrogen atoms on both sides to be equal

  7. Tips for balancing equations • Balance compounds first and elements last • Balance hydrogen and oxygen last as they often appear in more than one product. • Once you think the equation is balanced, do a final check by counting the atoms of each element one more time.

  8. Balance the following • Mg + O2  MgO • Li + Br2  LiBr • Al + CuO  Al2 + Cu Answers • 2Mg + O2  2MgO • 2Li + Br2  2LiBr • 2Al + 3CuO  Al2 O3+ Cu

  9. Sample Problem • Ammonia, NH3 is produced from the reaction of nitrogen gas and hydrogen gas. Write a balanced chemical equation for this reaction. • Word Equation: Nitrogen + hydrogen  ammonia • Skeleton Equation: N2 + H2  NH3 • Balanced Equation N2+ 3H2  2NH3

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