1. Chemical Equations and Reactions
What are they?

2. The Two Sides of a Chemical Reaction
Na + Cl  NaCl
Definition: A chemical change – one or more substances are changed into new substances.
The Two Sides of a Chemical Reaction
Reactant – About to be changed
Product – The new substance

3. Symbol for Chemical Equations
Pb(NO3)2 + 2KI  PbI2 + 2KNO3
“Pb(NO3)2” is a formula.
 Means produces (or yields)
+ Means added together
Coefficients – Number of molecules
Subscripts - Number of a particular atom in a molecule

4. Father of modern chemistry
Antoine Lavoisier
First Described the “Law of Conservation of Matter”

5. Conservation of mass HgO Hg + O2
Antoine Lavoisier found that the mass of the reactants and the products are equal, even when the states of matter change.
0.7g Oxygen became a gas
HgO
Hg + O2
He started with: 10g of Mercury Oxide (HgO)
He ended up with: and 9.3g Mercury…
...But what happened to the O2?
10 g. = g.
This is the Law of the Conservation of Matter – Matter is neither created or destroyed

6. Hg (mercury) can exist by itself... This Balances the equation!
Lavoisier’s chemical equation: 2
HgO  2
Hg + O2
Hg (mercury) can exist by itself...
but, Oxygen will need to bond
with another oxygen to make O2
To balance the atoms we need to:
Put the coefficient of 2 in front of reactant HgO
Put the coefficient of 2 in front the product Hg
This Balances the equation!

7. Easy, Right?
Not that easy?
Let’s try...

8. VISUALIZING to balance an Equation…

9. Equations must be balanced
H2 O
H2 + O2
Law of Conservation of Mass

10. Equations must be balanced
2 H2 O
2 H2 + O2
Matter is neither created or destroyed

11. N2 H2 NH3 Why or Why Not? Is this reaction possible?11
Is this reaction possible? N2 H2
NH3
Why or Why Not?
Let’s Count the Atoms: N H N H
There are 2 nitrogen atoms
There are 2 hydrogen atoms
1 nitrogen and 3 hydrogen…

12. Before we get balancing let’s look at a couple of rules.

13. Atoms can only bond in certain ways..H2 N2 N H2 H N2 H N H H2 H2 H N
That’s why we can’t change the subscripts. N2 H2 H N N2 N N2 N H

14. I can’t live without you!
Here is what it means...
Subscripts - Small #’s below an element.
Coefficients - Large #’s in front of the formulas. H2
2H2 H H
I can’t live without you! H
When balancing equations we
can only change the Coefficients!

15. 1 N2 1 H2 1 NH3 We can only change coefficients before the symbols15
Now, back to the balancing... 1 N2 1 H2 1
NH3
We can only change coefficients before the symbols N H N H
1 molecule of nitrogen
1 molecule of
hydrogen
1 molecule of ammonia

16. There are too many nitrogen atoms and not enough hydrogen atoms
After counting the atoms we know... N H N H
There are too many nitrogen atoms and not enough hydrogen atoms

17. A little common sense math goes a long way in making this equation balance…
There are 2 nitrogen atoms.
We will 2 more molecules for a total of 6 hydrogen atoms.
That will make 2 NH3 N H H N H H N H
Count the atoms. Is it balanced?

18. Then it’s a balanced equation
Do both sides have the same amount of Atoms? N H H N H H N H
N H NH3
Then it’s a balanced equation

19. Four Steps to Balance Equations:
1. Set up your equation
Write the metals, nonmetals, oxygen, and hydrogen.
2. Count and then write the number of atoms you have on both sides.
3. Balance by changing the coefficients and recounting.
4. Start the process again if it still does not balance.

20. H2 + O2  H2O O H 1. Set up your equation
Write the elements in this order: Metals, Nonmetals, Oxygen, Hydrogen
H2 + O2  H2O O H

21. 2. Count and write the number of atoms you have of each on both sides.
H2 + O2  H2O 2 O 1 2 H 2

22. 3. Balance by changing the coefficients and recounting.2 2
H2 + O2  H2O O H 2 1
(2)
Need to have at least 2 “O”
(4)
(4)
But it changes the number of “H”
How are you going to make “H” add up to 4?
Is this balanced?
Yes!

23. Need to have at least 2 “Cl” Changing the Cl changes the “H”?
Let’s try another: 2
Mg + HCl  H MgCl2 1 Mg 1
(2) 1 Cl 2
Need to have at least 2 “Cl”
Is this balanced?
Yes! 2
Changing the Cl changes the “H”?
(2) 1 H

24. Na + HCl  NaCl + H2 Na Cl H 1 2 2 (2) Let’s try another:
In this case, we will start with hydrogen since it is the only one unbalanced.
(2)

25. Na + HCl  NaCl + H2 Na Cl H 1 2 (2) (2)
But, changing the Hydrogen in HCl effects the number of chlorine atoms. So you must change number on both sides to reflect the change.
Na + HCl  NaCl + H2 Na Cl H 1 2
(2)
(2)

26. Na + 2HCl  NaCl + H2 Na Cl H 1 2 (2) 2 (2)
But, changing the Hydrogen in HCl effects the number of chlorine atoms. So you must change the number on both sides to reflect the change.
Na + 2HCl  NaCl + H2 Na Cl H 1 2
(2) 2
(2)

27. Na + 2HCl  NaCl + H2 2 (2) 1 Na (2) Cl (2) H 2
Changing the chlorine on the product side effects the sodium (Na) on the reactants side. So we must now change it as well.
Na + 2HCl  NaCl + H2 Na Cl H 1 2
(2) 2
(2)
(2)

29. 4 Types of Chemical Reactions
Synthesis
Decomposition
Single Displacement
Double Displacement

30. Two or more substances combine to form a new one
Synthesis
A + B  AB
2H2 + O2  2H2O
Two or more substances combine to form a new one

31. AB  A + B 2MgO  2Mg + O2 Decomposition
The opposite of synthesis; substance breaks down into 2 or more simpler substances

32. A + BC  AC + B Zn + Cu(NO3)2  Zn(NO3)2 + Cu Single Displacement
Occurs when one element replaces another in a compound; a zinc strip is put into copper nitrate solution and the copper precipitates out (it turns solid)

33. Occurs when two element “switches” with one another compound;
Double Displacement
AB + CD  AD + CB
HCl + NaOH  HOH + NaCl
(H2O)
Occurs when two element “switches” with one another compound;