UNIT 4 - REACTIONS BALANCING EQUATIONS

WARM UP 7 minutes In a chemical reaction, what is meant by the terms “product” “reactant”? What type of reaction is this: CaSO4 + Mg(OH)2 --> Ca(OH)2 + MgSO4 Is the following reaction possible? Why or why not? Na + BaCl2  Ba + NaCl What are the products of the equation, Na2S + K  Chromium is characterized by a very high melting point. Use the PToE to identify which of these elements most likely has a similar melting point. Chlorine C. Bromine Manganese D. Krypton

AGENDA ESSENTIAL QUESTION: Warm Up Announcements Counting Atoms How do substances interact with each other to produce new ones? Warm Up Announcements Counting Atoms Balancing Equations Exit Quiz

ANNOUNCEMENTS Tutoring after school tomorrow. Sign up on website or DON’T SHOW UP. By Next Thursday 3.24.16, you should have completed and turned in ALL missing assignments. Upcoming Events: MIDTERMS!!! Will have everything up to the end of this Unit (Reactions). Upcoming Events: Unit 4 Test!!! Types of Reactions Predicting Products (Single and Double Replacement) Balancing Equations

Unit 4 – subtopic 2: BALANCING EQUATIONS The Law of Conservation of Mass Counting Atoms Balancing Equations

THE LAW OF CONSERVATION OF MASS

What’s up with the apples?

What about these 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.

Chemical Reaction Notes 1. Law of Conservation of Mass Mass is neither created nor destroyed – it is simply converted from one form to another. 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 There are three rules for counting atoms: Subscripts apply to the element immediately before it. Coefficients multiply the entire molecule. If there are parentheses, the subscript multiplies everything inside the parentheses.

Counting Atoms Rules 1. Subscripts apply to the element immediately before it Ex) MgCl2 #Mg ____ #Cl_____ 2. Coefficients multiply the entire molecule Ex) 2C2H6 #C___ #H____

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

Counting Atoms 3P6(BrO3)3 1. H2SO4 2. Ca(OH)2 3. NaCl 4. (NH3)3PO4 Example: Your turn: How many atoms of each element are in the following molecules? 1. H2SO4 2. Ca(OH)2 3. NaCl 4. (NH3)3PO4 5. 3H2O 3P6(BrO3)3

BALANCING EQUATIONS

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 it balanced?

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

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

Balancing Chemical Reactions Ex 1: ____N2 + ____H2  ___NH3

Balancing Chemical Reactions Ex 2: ____FeO  ____Fe + ____O2

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

Partner Practice 1. ____NO + ____O2  ___NO2

Partner Practice 2. ____H2 + ____Cl2  ___HCl

Partner Practice 3. ____Fe + ____Cl2  ___FeCl3

Partner Practice 4. ____CH4 + ____O2  ___CO2 + ___H2O

Partner Practice 5. ____ K + ____ Cl2  ____ KCl   6. ____ N2 + ____ F2  ____ NF3

Independent Practice For the rest of class Go to the class website and copy notes (in blue). Unit 4: Reactions Balancing Equations Work on and complete Worksheet 4.2. Show your work in balancing equations on the back of the worksheet. When 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.

Exit Ticket Balance the following equations: ___Na + ___Cl2  ___NaCl ___Al + ___HBr  ___AlBr3 + ___H2