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Notes chemical equations


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  • 1. TEKS 8.5D recognize that chemical formulas are used to identify substances and determine the number of atoms of each element in chemical formulas containing subscripts TEKS 8.5F recognize whether a chemical equation containing coefficients is balanced or not and how that relates to the law of conservation of mass Balancing Chemical Equations
  • 2. A chemical reaction occurs when the chemical bonds between elements are formed or broken.
  • 3. This requires a gain or loss of energy.
  • 4. A chemical equation is a short, simple way to describe a chemical reactions using symbols and formulas instead of words.
  • 5. Reactants are the substances you begin with in a chemical reaction.
  • 6. These are shown to the left side of an arrow called the yield sign. Fe + 2 HCl reactants FeCl2 yield sign + products H2
  • 7. During a chemical reaction, the atoms rearrange to form new bonds between atoms.
  • 8. Products are the substances you end with in a chemical reaction.
  • 9. Products are shown to the right of the yield sign arrow. Fe + 2 HCl reactants FeCl2 yield sign + products H2
  • 10. The products formed in a chemical reaction have different properties from the reactants.
  • 11. A yield sign is used to show the direction of the chemical reaction. Fe + 2 HCl FeCl 2 + H 2
  • 12. A chemical equation is read like this: Fe + 1 atom of iron 2 HCl 2 molecules reacts of with hydrochloric acid FeCl2 + to yield 1 molecule of Iron chloride H2 1 and molecule of hydrogen
  • 13. During a chemical reaction, atoms cannot be created or destroyed, so the number of atoms at the beginning of a reaction MUST equal the number at the end of the reaction!
  • 14. This is called the Law of Conservation of Mass.
  • 15. This law also means that the mass of the reactants must equal the mass of the products.
  • 16. What if the number of atoms in the reactants does not match the number in the products?
  • 17. C3H8 + O2 mass =76 grams 3-carbon 8-hydrogen 2-oxygen CO2 + H2O mass = 62 grams 1-carbon 2-hydrogen 3-oxygen
  • 18. The Law of Conservation of Mass says that the number of each atom must be equal on both sides of the yield sign along with the masses. Let’s balance the equation using some basic rules.
  • 19. Basic Rules for Balanced Equations
  • 20. Chemical formulas CANNOT be altered!
  • 21. When balancing an equation, the subscript cannot be changed. Don’t change me! H 2O
  • 22. Coefficients can be added before an element or molecule.
  • 23. C3H8 + 5 O2 => 3CO2 + 4 H2O Add coefficients to the equation to balance the number of atoms
  • 24. C3H8 + 5O2 => 3CO2 + 4H2O 3-carbon 8-hydrogen 10-oxygen 3-carbon 8-hydrogen 10-oxygen Atoms on each side are equal!!
  • 25. Coefficients were used to balance the number of atoms on each side of the chemical equation.
  • 26. C3H8 + 5O2 => 3CO2 + 4H2O mass = 204 grams =>mass = 204 grams If we mass the reactants and products before and after the reaction, the masses are equal. We have followed the law!