UNIT 1 Matter Day 25 October 4, 2017 Law of Conservation of Mass Earth and Environmental Science

Turn in lab sheet from yesterday’s lab on Law of Conservation of Mass. Pick up the study guide from the front table. Science Starter: Copy the question. Choose an answer and write the entire answer in your response box. Q - How does the zig-zag line on the periodic table help indicate properties of elements?  *Elements located on the left of the zig-zag line are liquids at room temperature. *Elements located on the right of the zig-zag line are liquids at room temperature. *Elements located on the left of the zig-zag line are good conductors of heat and electricity. October 4, 2017

Plan for today: “Modeling Molecules” lab Continue lesson on Law of Conservation of Mass- counting atoms/balancing chemical equations: *notes/discussion *video *practice

Homework: 1. Quiz next Monday over elements, compounds, and mixtures/Law of Conservation of Mass/Balancing Chemical Equations 2. Chemistry Unit Test next Friday, Oct. 13th 3. Begin working on the Chemistry Exam study guide. I will take it up next Friday and grade it. It will be a good bit of work, so get started and work on it every night. Pace yourself.

E.Q. Page 11 What happens to atoms during chemical reactions?

H C O N Before we start our “Modeling Molecules” activity, please: Draw 4 large boxes at the top of the lab sheet. Write the chemical symbols and other info. in the boxes as they are shown below. Draw a Lewis Structure (dot diagram) for each of the elements. Fill in the # of electrons needed to fill the atom’s outer shell. H C O N Needs ___ elec. Needs ___ elec. Needs ___ elec. Needs ___ elec.

Let’s read about “Modeling Molecules”. Read intro info. Comparing molecule models to Lewis Structures. The WHY of it all! COMPOUNDS! Do not get ahead in the lab. We will make the molecules together. When the first 6 molecules have been made and drawn, turn over to the back and do the analysis questions. You will need your periodic table. If you finish the analysis questions early, you may do Part B of the lab.

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

Now to the notes on the LAW OF Conservation of Mass.

Copy these 3 examples. Chemical Formulas Def. Chemical formula is a combination of chemical symbols and numbers to represent a substance.It shows how many atoms of each kind of element are present in a molecule. Subscript: a number written to the lower right of a chemical symbol. It tells how many atoms of that element are present. Copy these 3 examples.

Chemical Formulas Def. Chemical formula is a combination of ____________ ___________and ____________ to represent a ___________.It shows how many __________ of each kind of ___________ are present in a ____________. Subscript: a number written to the _________ __________ of a chemical ___________ . It tells how many ___________ of that element are present.

chemical Equations Def. Use chemical symbols and formulas to describe a chemical reaction. Ex: Copy this Chemical equation. C and O2 are the reactants. CO2 is the product. yields

Chemical Equations Def. - Use chemical ____________ and ____________ to describe a ____________ ____________.

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

Law of Conservation of Mass Def. This law states that ______________ CANNOT be _____________ or _____________ in ordinary ______________or ________________ ________________. The total __________________________________________ ______________________________________________________. This can be proven in a __________ ___________…one in which nothing enters or leaves the system.

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

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.

Before we practice balancing equations, let’s practice counting atoms. Practice Counting Atoms worksheet

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.

*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

*Coefficient: a number that is placed ____________ a chemical _________ or _________ in order to __________ a chemical ___________. Subscripts __________ be _________ to balance an equation. Why? H2O 2H20 -2 molecules of water CO2 4CO2 – 4 molecules of carbon dioxide C6H12O6

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 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).

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

Before we practice balancing equations, let’s practice counting atoms. Practice Counting Atoms worksheet

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.

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.

Wrap-up: Any questions?