Balancing Chemical Reactions
Making new substances
Main Ideas
Chemical Reactions are represented by Chemical
Equations.
Chemical Equations are balanced to show the same
numb...
Today you will
learn how to
balance a chemical
equation.
Why?
• All recipes are balanced
chemical reactions.
• The difference between a
campfire and an explosion
is a balanced che...
And
The difference between:

CH4 + O2 → CO2 + H2O

is
CH4 + 2 O2 → CO2 + 2 H2O
Law of Conservation of
Mass
In a chemical reaction, matter is neither created nor
destroyed.
Atoms won’t change their iden...
Let’s learn how to do this…
Oh No… Vocabulary (but wait,
you already know this)
Reactants:

Products:

substance that takes part in
and undergoes chan...
Balancing Equations
After you write a chemical equation you have to balance it to
make sure that the same number of atoms ...
Steps to Balancing a Chemical
Equation

Get yourself an unbalanced
equation.

Li + H2O  H2 + LiOH
Steps to Balancing a Chemical
Equation

Draw boxes around all the
chemical formulas.
Never, ever, change anything inside t...
Steps to Balancing a Chemical
Equation
Make an element inventory.
How are you going to know if the equation is balanced if...
Steps to Balancing a Chemical
Equation

Li + H2O  H2 + LiOH
Li
H
O

1
2
1

Li
H
O

1
3
1
Steps to Balancing a Chemical
Equation

Write coefficients in front of each
of the boxes (molecules) until the
inventory f...
Steps to Balancing a Chemical
Equation

Li + H2O  H2 + LiOH
Li
H
O

1
2
1

Li
H
O

I need more hydrogens in the reactant ...
Steps to Balancing a Chemical
Equation

Li + 2 H2O  H2 + LiOH
Keep the inventory current…

Li
H
O

1
2
1

1
4
2

Li
H
O

...
Steps to Balancing a Chemical
Equation

Li + 2 H2O  H2 +2 LiOH
Keep the inventory current…

Li
H
O

1
2
1

1
4
2

Li
H
O
...
Steps to Balancing a Chemical
Equation

2 Li + 2 H2O  H2 + 2 LiOH
Keep the inventory current…

Li
H
O

1
2
1

2
4
2

Yay!...
Ok, let’s do this together
Using the set of cards you have, replicate this
equation

H2 + O2

H2 O
Inventory the atoms
Write this in your sheet

H2 + O2
2
2

H2 O
2
1
What do I need?
Add a coefficient
More oxygen.

Inventory!

H2 + O2

2 H2 O
2
1

2
2
NOT DONE! I need more
hydrogen in the reactants side!...
Add another coefficient
Add more hydrogen in the reactant side.

2 H2 + O2
2
2

4
2

2 H2 + O2 → 2 H2O

Inventory!

2 H2 O...
Your Turn.
At your tables, use the cards to correctly balance the
equations. Write down your answers in your in your
sheet...
Super Saver Tips
Remember to simplify. If ALL THE COEFFICIENTS share a
divisor, simplify. Just like when working with frac...
Upcoming SlideShare
Loading in …5
×

Intro to balancing chemical reactions

1,031 views

Published on

Introduction to balancing chemical reactions for middle school science

Published in: Education, Technology, Business
0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
1,031
On SlideShare
0
From Embeds
0
Number of Embeds
9
Actions
Shares
0
Downloads
39
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide
  • Pass out materials
  • Pass out materials
  • Pass out materials
  • Pass out materials
  • Intro to balancing chemical reactions

    1. 1. Balancing Chemical Reactions Making new substances
    2. 2. Main Ideas Chemical Reactions are represented by Chemical Equations. Chemical Equations are balanced to show the same number of atoms of each element on each side. The Law of Conservation of Mass says that atoms won’t be created or destroyed in a chemical reaction.
    3. 3. Today you will learn how to balance a chemical equation.
    4. 4. Why? • All recipes are balanced chemical reactions. • The difference between a campfire and an explosion is a balanced chemical reaction. • Knowing how many antacid tablets to take after eating Taki’s is a balanced chemical reaction
    5. 5. And The difference between: CH4 + O2 → CO2 + H2O is CH4 + 2 O2 → CO2 + 2 H2O
    6. 6. Law of Conservation of Mass In a chemical reaction, matter is neither created nor destroyed. Atoms won’t change their identity (e.g. a Carbon atom can’t become an Iron atom) This means that you have to have the same number of each type of atom on each side of the chemical equation. Conservation of Mass Video
    7. 7. Let’s learn how to do this…
    8. 8. Oh No… Vocabulary (but wait, you already know this) Reactants: Products: substance that takes part in and undergoes change during a reaction. substance that is formed as the result of a chemical reaction. CH4 + 2 O2 CO2 + 2 H2O Subscript Coefficient Indicates a reaction has : tells taken place. Read as “yields” : you how many atoms you tells in a molecule. molecules have you how many If no you have. means you have subscript itIf no coefficient it means you one atom. have one molecule.
    9. 9. Balancing Equations After you write a chemical equation you have to balance it to make sure that the same number of atoms of each element are on each side. How would you balance this equation? Li + H2O  H2 + LiOH
    10. 10. Steps to Balancing a Chemical Equation Get yourself an unbalanced equation. Li + H2O  H2 + LiOH
    11. 11. Steps to Balancing a Chemical Equation Draw boxes around all the chemical formulas. Never, ever, change anything inside the boxes. Ever. Really. If you do, you're guaranteed to get the answer wrong. Li + H2O  H2 + LiOH
    12. 12. Steps to Balancing a Chemical Equation Make an element inventory. How are you going to know if the equation is balanced if you don't actually make a list of how many of each atom you have? You won't. You have to make an inventory of how many atoms of each element you have, and then you have to keep it current throughout the whole problem. How? Use the skills you learned on counting atoms
    13. 13. Steps to Balancing a Chemical Equation Li + H2O  H2 + LiOH Li H O 1 2 1 Li H O 1 3 1
    14. 14. Steps to Balancing a Chemical Equation Write coefficients in front of each of the boxes (molecules) until the inventory for each element is the same both before (reactants) and after products) the reaction.
    15. 15. Steps to Balancing a Chemical Equation Li + H2O  H2 + LiOH Li H O 1 2 1 Li H O I need more hydrogens in the reactant side… 1 3 1
    16. 16. Steps to Balancing a Chemical Equation Li + 2 H2O  H2 + LiOH Keep the inventory current… Li H O 1 2 1 1 4 2 Li H O 1 3 1 Oh snap, now I need more hydrogens and oxygens in the product side…
    17. 17. Steps to Balancing a Chemical Equation Li + 2 H2O  H2 +2 LiOH Keep the inventory current… Li H O 1 2 1 1 4 2 Li H O 1 3 1 2 4 2 Looks like we are getting somewhere, but I need more lithiums in the reactant side…
    18. 18. Steps to Balancing a Chemical Equation 2 Li + 2 H2O  H2 + 2 LiOH Keep the inventory current… Li H O 1 2 1 2 4 2 Yay! A balanced equation. Li H O 1 3 1 2 4 2
    19. 19. Ok, let’s do this together Using the set of cards you have, replicate this equation H2 + O2 H2 O
    20. 20. Inventory the atoms Write this in your sheet H2 + O2 2 2 H2 O 2 1 What do I need?
    21. 21. Add a coefficient More oxygen. Inventory! H2 + O2 2 H2 O 2 1 2 2 NOT DONE! I need more hydrogen in the reactants side! 4 2
    22. 22. Add another coefficient Add more hydrogen in the reactant side. 2 H2 + O2 2 2 4 2 2 H2 + O2 → 2 H2O Inventory! 2 H2 O 2 1 4 2 NOT DONE! Check your work and write the final balanced equation
    23. 23. Your Turn. At your tables, use the cards to correctly balance the equations. Write down your answers in your in your sheets.
    24. 24. Super Saver Tips Remember to simplify. If ALL THE COEFFICIENTS share a divisor, simplify. Just like when working with fractions. If you see repeating entities such as (SO4), (PO4), (MnO4), (OH) in BOTH sides , treat them as one atom. Na3PO4 + KOH → NaOH + K3PO4 Na PO4 K OH 3 1 1 1 3 1 3 3 Na PO4 K OH 1 1 3 1 3 1 3 3 Na3PO4 + 3 KOH → 3 NaOH + K3PO4 If you have H2O in one side and OH in the other, rewrite the water as H-OH and treat the OH (hydroxide) as one atom.

    ×