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Law of Conservation of Mass in Chemical Reactions

Learn about the Law of Conservation of Mass in chemical reactions, how to count atoms on each side of a chemical equation, and how to balance equations.

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Law of Conservation of Mass in Chemical Reactions

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  1. SPI 0807.9.11 Law of Conservation of Mass Science Notes Tennessee SPI Objective: Recognize that in a chemical reaction the mass of the reactants is equal to the mass of the products. (Law of Conservation of Mass: LOCOM) Essential Question(s) How do I determine the number and type of atoms on each side of a chemical equation? I Can Statement I can count the numbers of atoms on each side of chemical reactions. Success Criteria I can prove that I understand LOCOM by counting the number of atoms on each side of chemical reactions.

  2. SPI 0807.9.11 Law of Conservation of Mass Science Notes Tennessee SPI Objective: Recognize that in a chemical reaction the mass of the reactants is equal to the mass of the products (Law of Conservation of Mass: LOCOM) • No atoms are created or destroyed during chemical reactions So no mass is created or destroyed This is called the Law of Conservation of Mass LOCOM

  3. SPI 0807.9.11 Law of Conservation of Mass Science Notes Two Parts of Chemical Equations (1) Reactants (2) Products Reactants: chemicals you start with in a reaction Products: chemicals you end up with in a reaction 2H2 + O2 2H2O Reactants (Hydrogen & Oxygen) Product (water)

  4. SPI 0807.9.11 Law of Conservation of Mass Science Notes Subscript: small number below & to the right of a chem symbol • reveals the number of atoms Coefficient: big number in front of a chemical symbol or formula • (tells you to multiply) Yields Arrow: always points towards the products 2H2 + O2 2H2O Three key symbols in chemical equations (1) Subscript (2) Coefficient (3) Yields Arrow

  5. All chemical reactions always obey the… …Law of Conservation of Mass Atoms are never created or destroyed in a chemical reaction … they are just rearranged. Wrong Example: Look at the unbalanced equation shown below. It is written incorrectly. H2 + O2 H2O It DOES NOT obey this law. Therefore it is impossible for this reaction to occur like this. (count the atoms on each side of the equation) 2 & 1 2 & 2 Four is not equal to three!

  6. F.Y.I. Balancing Equations: Note: You will learn about this in more detail in High School. 2H2 + O2 2H2O You make the amount of reactants equal the amount of products. We use coefficients to do this. Example: Here is the same equation from the previous slide, but now I have balanced it by placing coefficients. (count the atoms on each side of the equation) 4 & 2 4 & 2 Six is equal to Six! Now it demonstrates the law of conservation of mass.

  7. Quick Review SPI 0807.9.11 Law of Conservation of Mass Science Na+ Cl2 2NaCl How many sodium (Na) reactants? How many sodium (Na) products? How many chlorine (Cl) reactants? How many chlorine (Cl) products? Does this demonstrate the law of conservation of mass? (count the atoms on each side) One Two Two Two No it does not! (What is wrong with it?) Note:Look at the sodium atoms on each side

  8. Quick Review SPI 0807.9.11 Law of Conservation of Mass Science 2N2+ O2 2N2O How many nitrogen (N) reactants? How many nitrogen (N) products? How many oxygen (O) reactants? How many oxygen (O) products? Does it demonstrate the law of conservation of mass? (count the atoms on each side) Four Four Two Two Yes it does! (Count the atoms) Why? Same number of atoms on each side

  9. SPI 0807.9.11 Law of Conservation of Mass Science Review Six Three Six Six 2 4 2 1 4 2 4 2 Hint: Count the atoms on each side of the arrow

  10. SPI 0807.9.11 Law of Conservation of Mass Science Review Two Four Eight Eight 1 2 1 2 2 6 6 2 Hint: Count the atoms on each side of the arrow

  11. SPI 0807.9.11 Law of Conservation of Mass Science Review Reactants: 2g + 4g = 6g Products: 6g Hint: Count the amounts of reactants and products

  12. SPI 0807.9.11 Law of Conservation of Mass Science Review Hint: Use substitution: K= 39 grams, O= 32 grams …so 39 + 32 ???

  13. SPI 0807.9.11 Law of Conservation of Mass Science Review Products: 7g Reactants: 4g + 3g = 7g Reactants: 5g + 5g = 10g Products: 20g + 5g = 25g Hint: Count the amounts of reactants and products.

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