1. Catalyst
1. To fill up a cup with water, let’s say you need 5 billion molecules of water. How many atoms of hydrogen is that? How many atoms of oxygen? 2. When you heat up food in the microwave, how do you know how long to set it for?

2. Balancing Chemical Equations
Atoms must be conserved!

3. Counting Atoms 1. H2SO4 2. CaOH2 3. NaCl 4. (NH3)3P04 5. 3H2O
How many atoms of each element are in the following molecules?
1. H2SO4
2. CaOH2
3. NaCl
4. (NH3)3P04
5. 3H2O

4. Answers 1. 2 hydrogen, 1 sulfur, 4 oxygen
2. 1 calcium, 1 oxygen, 2 hydrogen
3. 1 sodium, 1 chlorine
4. 3 nitrogen, 9 hydrogen, 1 phosphorus, 4 oxygen
5. 6 hydrogen, 3 oxygen

5. Is this equation balanced?
NaCl + H2O  NaOH + Cl2
left side has 1Na, 1Cl, 2H, and 1O
right side has 1Na, 1O, 1H, and 2Cl
NO! It is not balanced!

6. Is this equation balanced?
HCl + NaOH NaCl+ H2O
left side has 2H, 1Cl, 1Na, and 1O
right side has 1Na, 1Cl, 2H, and 1O
Yes! It is balanced!

7. Is this equation balanced?
Ca + H2O Ca(OH)2 + H2
left side has 1Ca, 2H, 1O
right side has 1Ca, 2O, 4H
No! It is not balanced!
How can we make it balance?

8. Ca + H2O  Ca(OH)2 + H2
We need more H’s, but we can’t add just the H atom, we have to add the entire molecule the H is attached to:
Ca + H2O Ca(OH)2 + H2
H2O
Count the boxes. These are the coefficients:
1 Ca + 2 H2O  1 Ca(OH) H2

9. 1 Ca + 2 H2O  1 Ca(OH) H2
Just like in math, this equation may be written in a simpler way:
Ca + 2 H2O Ca(OH)2 + H2

10. What is balanced in a chemical equation?
Three things are balanced in a chemical equation:
1. Atoms
2. Mass
3. Charge

11. For now, you will only be concerned with balancing atoms
For now, you will only be concerned with balancing atoms. Remember, the number of atoms of each element on the reactants side must equal the number of atoms of each element on the products side!

12. The End
Let’s practice!