LOCOM Notes Science Tennessee SPI Objective: Law of Conservation of Mass Notes Science 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

Law of Conservation of Mass Two Parts of Chemical Equations SPI 0807.9.11 Law of Conservation of Mass Notes Science 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)

Law of Conservation of Mass Three key symbols in chemical equations SPI 0807.9.11 Law of Conservation of Mass Notes Science 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

H2 + O2 H2O 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. 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) H2 + O2 H2O 2 & 2 2 & 1 Four is not equal to three!

2H2 + O2 2H2O F.Y.I. Balancing Equations: 4 & 2 4 & 2 Note: You will learn about this in more detail in High School. 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) 2H2 + O2 2H2O 4 & 2 4 & 2 Six is equal to Six! Now it demonstrates the law of conservation of mass.

Na + Cl2 2NaCl Science Quick Review How many sodium (Na) reactants? 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

2N2 + O2 2N2O Science Quick Review How many nitrogen (N) reactants? 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

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

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

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

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

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