Science Starter Write a letter (at least 4 sentences) to a student who was absent Friday. What did we learn? Make sure to include the following words: Products -Reactants Synthesis -Decomposition Single Replacement -Double Replacement Combustion -Oxidation Reduction Take out your HW!

Objective SWBAT count atoms in chemical reactions and balance them, as per the Law of Conservation of Mass.

Agenda Science Starter Balancing Equations Exit Ticket/Homework Law of Conservation of Mass Counting Atoms What is oxidized and reduced? Exit Ticket/Homework Lab Wednesday Test Friday Midterm Tues/Wed *No tutorial today*

What’s up with the apples?

How ‘Bout Them Apples

Chemical Reactions  Br Br Br Br Li Li Li Li

For the rest of today, we will be balancing chemical equations. This will seem like a bunch of rules a chemist made up unless you understand the following concepts.

Unit 4: Chemical Reactions Counting Atoms Balancing Equations

Chemical Reaction Notes 1. Law of Conservation of Mass: in a chemical reaction, the mass of the products equals the mass of the reactants. What is the Law of Conservation of Matter? 2. Chemical reactions MUST BE BALANCED The number of atoms on the reactant side and the product side must be EQUAL But how do we count the number of atoms?

Counting Atoms Rules 3P6Cl3 1. Subscripts apply ONLY to the element before Ex) MgCl2 #Mg ____ #Cl_____ 2. Coefficients multiply the entire molecule Ex) 2C6H2 #C___ #H____

Counting Atoms Rules 3. If there are parentheses, the subscript multiples everything inside the parentheses Ex) 3Be(NO3)2 #Be___ #N____ #O____

Counting Atoms 1. H2SO4 2. Ca(OH)2 3. 4NaCl 4. 2(NH3)3PO4 5. 3H2O How many atoms of each element are in the following molecules? 1. H2SO4 2. Ca(OH)2 3. 4NaCl 4. 2(NH3)3PO4 5. 3H2O

To decide if an equation is balanced, compare the number of atoms of each element that appear on each side of the equation. If the number of atoms is equal then the equation is balanced, if not equal than the equation is not balanced Ex) N2 + 3 H2  2 NH3 Is it balanced?

You Try! C3H8 + 5 O2  3 CO2 + 4 H2O Is is balanced?

Ok, cool. BUT HOW DO WE BALANCE THESE BAD BOYS????!!!

(never change subscripts!) When balancing… Step 1: Draw a line between products and reactants Step 2: Tally up atoms of each element on each side Step 3: Change coefficients to start balancing (never change subscripts!) Step 4: Recalibrate each time you change a coefficient Step 5: CHECK YOUR WORK!

Balancing Chemical Reactions Notes Balancing Chemical Reactions Ex 1: ____N2 + ____H2  ___NH3 What is oxidized? What is reduced?

Balancing Chemical Reactions Notes Balancing Chemical Reactions Ex 2: ____FeO  ____Fe + ____O2 What is oxidized? What is reduced?

____Fe + ____Cl2  ___FeCl3 4. ____CH4 + ____O2  ___CO2 + ___H2O The best way to learn this is to practice. With a partner, balance the following equations: ____NO + ____O2  ___NO2 ____H2 + ____Cl2  ___HCl ____Fe + ____Cl2  ___FeCl3 4. ____CH4 + ____O2  ___CO2 + ___H2O What is oxidized? What is reduced?

Partner Practice 1. ____NO + ____O2  ___NO2

Partner Practice 2. ____H2 + ____Cl2  ___HCl

3. ____Fe + ____Cl2  ___FeCl3 Partner Practice 3. ____Fe + ____Cl2  ___FeCl3

4. ___CH4 + ___O2  ___CO2 +___H2O Partner Practice 4. ___CH4 + ___O2  ___CO2 +___H2O

Independent Practice For the rest of class, work on (and complete, if possible) Worksheet 4.2 If you get done: come and see me. If you are done, I will have you check your answers against my answer key. If you get any wrong, you must go back and fix them. If you get done with that: You may help a neighbor