1. #52 Counting Atoms WS #53 Balancing equations notes

2. Description Physical or Chemical Property or change
The play-do is stringy
A teacher has brown hair
Cotton can burn easily
Water boils at 100*C
Gold does not tarnish when exposed to water (H2O)
The pot keeps the food warm

3. Count the atoms
4 Al(OH)3
3(NH3)3(PO4)2

4. Chemical Equation Vocab
2H O2  2H2O
Coefficient – a # that is in front of the element or compound and distributed to ALL associated elements or compounds
Subscript – identifies the amount of atoms in an element
Reactant(s) – the starting material in a chemical reaction (on the left)
Product(s) – the substance formed from the chemical reactants ( on the right)
Yield – like a equal sign; separates the products from the reactants

5. *Law of conservation of mass/matter
The Law of Conservation of Mass/Matter states that matter cannot be created or destroyed
Meaning, the number of atoms each element has MUST be equal on both sides of the chemical equation
A way to remember this is:
What goes in must come out

6. Chemical equations MUST be balanced!
Why?
Because the Law of Conservation of Mass or Matter

7. So how do I balance equations?
*When balancing equations, you CANNOT change the subscripts!
*If you change the subscript, you change the substance
For example:
H H2O2

8. *So how do you make #’s work if you cannot change subscripts?
You change the COEFFICIENTS and recount the atoms

9. *Rules for balancing equations (be prepared to use your eraser)
Draw an line underneath the yield sign of the equation. Count ALL atoms on both sides of the equation.
Pick an element that is not equal on both sides and find the least common multiple.
Add coefficient to the chosen element and recount atoms
Repeat steps 2 and 3 for unbalanced elements and recount atoms. (Until all elements are even)
Write the balanced equation
Fe Cl2  FeCl3
Is it balanced?

10. Let’s try these two together
Na Cl2  NaCl
Mg N2  Mg3N2

11. Balance the equations
Mg N2  Mg3N2
Cr O2  Cr2O3
NH O2  N H2O
Na3PO CaCl2  NaCl Ca3 (PO4)2
Mg(NO3) K3PO4  Mg3(PO4) KNO3

12. You try
Cr O2  Cr2O3
NH O2  N H2O

13. Na3PO4 + CaCl2  NaCl + Ca3(PO4)2

14. extra

15. Bonus problem…
Mg(NO3) K3PO4  Mg3(PO4) KNO3