UNIT 1 Matter Day 35 October 18, 2017 Law of Conservation of Mass 8th Grade Science

October 18, 2017 1. Turn in your lab sheet. 4. 2. Science Starter: Copy this question-Which does silicon dioxide (SiO2) represent?   A. element B. compound C. homogeneous mixture D. heterogeneous mixture October 18, 2017

Plan for today: Lesson – Continuing Law of Conservation of Matter (Mass) a. Notes b. Balancing chemical equations

Homework: On the “Balancing Act Practice” worksheet, do problems 1-7. Use the sheet with the steps to help you.

E.Q. What is the Law of Conservation of Matter/Mass?

Take out your notes called “Law of Conservation of Mass” and let’s fill in some information.

Law of Conservation of matter (Mass) Def. This law states that matter (mass/atoms) CANNOT be created or destroyed in ordinary physical or chemical changes. A.D. The total mass of the reactants equals the total mass of the products. A.D. This can be proven in a closed system… one in which nothing enters or leaves the system. 10g 20g 30g

Conservation of Mass in a closed system

What did you observe in the law of conservation of mass lab yesterday? What evidence of a chemical change did you observe? How did the mass of the products compare to the mass of the reactants? If the mass was different afterwards, what might be some possible reasons?

Now let’s learn how to balance chemical equations. A Quick Review elements Chemical symbols represent __________. compounds Chemical formulas represent __________. Chemical equations represent __________. chemical reactions. Now let’s learn how to balance chemical equations.

Now let’s learn how to balance chemical equations. A Quick Review Chemical symbols represent __________. Chemical formulas represent __________. Chemical equations represent __________. Now let’s learn how to balance chemical equations.

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

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.

Let’s look at some equations and determine if they are balanced Let’s look at some equations and determine if they are balanced. Turn on the back of the “How to Count Atoms” homework. Let’s do Part B (diagramming, counting atoms, and “Is the equation balanced?”) Then, I’ll teach you how to balance equations. Think of them as a math problem that has to be solved.

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.

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.

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

Let’s see how well you’ve been listening. Complete this phrase. Changing a subscript is a no-no because changing a subscript… changes the substance. (When we balance equations, we aren’t changing the substances…but we may have to change how many molecules there are of each substance. So, we use coefficients.)

Turn to the back of your “Find the Image” worksheet (balancing act) Turn to the back of your “Find the Image” worksheet (balancing act). Let’s practice balancing a few chemical equations together.

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

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.

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

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.

Wrap-up: Any questions?