1. UNIT 1 Matter Day 26 October 5, 2017
Law of Conservation of Mass -Balancing Chemical Equations
Earth and Environmental Science

2. Take out your notes on Law of Conservation of Mass.
October 6, 2016
Take out your notes on Law of Conservation of Mass.

3. Plan for today:
Continue discussing Law of Conservation of Mass- balancing chemical equations:
*Practice counting atoms
*Learn how to balance equations
*Practice, practice, practice!

4. Homework:
“Practice Counting Atoms” and “Balancing Act Practice” worksheets due tomorrow
Quiz Monday- Elements, compounds, mixtures/Law of conservation of mass and balancing chemical equations
Chemistry Unit Test Friday, Oct. 13th
Be working on the Chemistry Unit Test study guide. It’s due next Friday (test day).
Finish the “Modeling Molecules” analysis questions. Have them done by Monday.

5. E.Q. Page
What happens to atoms during chemical reactions?

6. Which of these 3 terms (element, molecule, compound) apply to the following? If a molecule, how many? O2
2H2O
4H2

7. Let’s look at the Law of Conservation of Mass and Chemical Equations presented Brainpop’s way.
Brainpop - Law of Conservation of Matter

8. Before we practice balancing equations, let’s practice counting atoms.
Coefficients are numbers used to balance equations. They always go IN FRONT OF a chemical formula.
Ex. 5H2O or 5(H2O) 5 is the coefficient. Multiply the coefficient by everything in the chemical formula. You should get 10H and 5O
Practice Counting Atoms worksheet

9. Let’s learn how to balance chemical equations.
Remember that the Law of Conservation of Mass/Matter states that in a chemical reaction, NO atoms are gained or lost. They just get rearranged to form NEW SUBSTANCES.

10. When we balance chemical equations, we are not changing the substances, but we may have to change the amount of some of the substances (how many molecules).
Coefficients are numbers used to balance equations. They always go IN FRONT OF a chemical formula, NEVER in the middle of it. Coefficients simply change HOW MUCH of a substance, but not what it is. 4CO2 means 4 molecules of carbon dioxide.

11. *Coefficient: a number that is placed in front of a chemical symbol or formula in order to balance a chemical equation. Subscripts CANNOT be changed to balance an equation. Why?
H2O 2H20 -2 molecules of water
CO2 4CO2 – 4 molecules of carbon dioxide
C6H12O6

12. More O2 in the reactants.
Count to be sure the number of atoms of each element is the same in the reactants and products.

13. How to Balance Chemical Equations: 3 Simple Steps
Step 1: Count the number of atoms for each element on both sides of the equation. Look for elements that are not balanced.
Ex. Mg O2 MgO
Mg- Mg-
O- O-
_____ is unbalanced.

14. Step 2: Add a coefficient in front of the formula that contains the unbalanced element(s). The O was unbalanced. Place a coefficient 2 in front of the MgO. ***Note: This may throw off the balance of other elements, so you have to keep working with it.
Ex. Mg O2 __ MgO
This will balance the O, but unbalance the Mg. So…add another coefficient 2 in front of the Mg in the reactant.
Ex. ___Mg O2 2 MgO
*This should balance the Mg but be sure to do Step 3.

15. Step 3: Check the number of atoms on both sides of the equation to be certain they are balanced.
2Mg O2 2MgO
Mg- Mg-
O- O-
Is it balanced? If so, you have supported the Law of Conservation of Matter (Mass).

16. How does balancing equations illustrate and support the Law of Conservation of Mass/Matter?
*Because they require that you have the same mass after the reaction as you do before the reaction. This means…
*The # and type of atoms are the same in the reactants and products (just in different combinations)
*Although the state of matter of the products may be different from the reactants, the overall mass doesn’t change.

17. In a chemical reaction, no atoms are gained or lost
In a chemical reaction, no atoms are gained or lost. They just get rearranged.
Because this Law of Conservation of Matter (Mass) has been proven, chemical equations (which represent a chemical reaction) MUST be balanced (same number of atoms on both sides).
mass of the reactants=mass of the products.

18. Let’s practice balancing some chemical equations
Let’s practice balancing some chemical equations. “Balancing Act” practice sheet.
Use pencil. You may have to change coefficients a few times.

19. Let’s look at Chemical Equations presented Brainpop’s way.
Brainpop-Chemical Equations

20. Wrap-up:
Any questions?