1. Chemical Reactions

2. Physical Change Any change where the composition does NOT change.
Can be reversible or irreversible
PHASE CHANGES are in this category!
Break, split, grind, cut, crush, tear, melting/boiling (points), etc.

3. Chemical Change The composition MUST change
Burn, rot, rust, decompose, ferment, explode, and corrode
Test before and after…

4. Reactant vs. Product Reactant: Present before reaction
Product: Produced in a reaction
The arrow is read “gives, yields, or reacts to produce”

5. You Try…
Label the reactant(s) and product(s) in the following reactions
CH4 + O2  CO2 + H2O
Hydrogen peroxide  water + oxygen
AB + CD  AD + CB
MgO  Mg + O2
Hydrochloric Acid + Magnesium  Magnesium Chloride + Hydrogen gas

6. Type 1
What do you think the Law of Conservation of Mass means? How might it relate to you, our class, or the environment? Fill at least 3 lines.

7. Zero A Scale

8. Law of Conservation of Mass
Mass is not created nor destroyed

9. Did the Following Obey? Why or why not?

10. Coefficients vs. Subscripts
Draw/write out the following:
2Cl
2Cl2
H2O vs. 3H2O
H3PO4 vs. 2H3PO4
We can write a chemical equation and see if it obeys…
2Al + Fe2O3  Al2O3 + 3Fe

12. Are the following consistent with the Law of Conservation of Mass
Are the following consistent with the Law of Conservation of Mass? Why or Why Not?
CaCl2 + 2NaOH  Ca(OH)2 + NaCl
2Cu + 2HCl  H2 + CuCl2
2Zn(s) + O2(g)  2ZnO(s)
C2H6 + 3O2  2CO2 + 3H2O
2NaOH + H2SO4  Na2SO4 + 2H2O
MgO + 2HC2H3O2  H2O + Mg(C2H3O2)2
6CO2(g) + 3H2O  C6H12O6 + 2O2(g)

13. Combustion and Bond Energy
Exothermic vs. Endothermic

14. Combustion and Bond Energy
Compounds contain chemical bonds
All chemical bonds contain different amounts of stored energy:
C-C C-N
348kJ 293kJ
Energy is required in order to break bonds
Energy is given off when bonds are formed

15. Chemical Reactions AB + CD  AD + CB A-B + C-D  A-D + C-B
Reactant bonds (A-B and C-D) must be broken
Product bonds (A-D and C-B) must be formed

16. Do the math…
Depending on the number and type of bonds broken and/or formed during chemical reactions, energy is either given off or required in chemical reactions
CH4 + 2O2  CO2 + 2H2O + 890kJ

17. CH4(g) + 2Cl2(g) + 2F2(g)  CF2Cl2(g) + 2HF(g) + 2HCl(g)
Calculations
Each compound must be drawn out in order to see and label bond energies *Use given sheet*
CH4(g) + 2Cl2(g) + 2F2(g)  CF2Cl2(g) + 2HF(g) + 2HCl(g)
Bonds broken-bonds formed will give you the overall energy in a reaction!
Reactants – Products

18. Exothermic vs. Endothermic
Exothermic: In a chemical reaction energy is given off (kJ is on the product side, or is negative)
Ex: CH4 + 2O2  CO2 + 2H2O + 890kJ
Endothermic: In a chemical reaction, energy is required (kJ is on the reactant side, or is positive)
Ex: N2 + O kJ  2NO
This relates to bond energy

19. Environmental Chemistry?!
The energy given off during certain chemical reactions can be captured and used (combustion reactions)!
Beneficial to humans 
CH4 + 2O2  CO2 + 2H2O