1. Chemical Reactions

2. How do you know that a chemical reaction has occurred?
Physical Observations
Color change
Precipitate
Heat
Bubbles
Smell

3. 3CO(g) + Fe2O3(s)  2Fe(s) + 3CO2(g)
Chemical Equation
REACTANTS
PRODUCTS
3CO(g) + Fe2O3(s)  2Fe(s) + 3CO2(g) ↑
# OF COMPOUNDS ↑
# OF ATOMS IN THE COMPOUND ↑
STATE SYMBOL

4. Balancing Chemical Equations
Law of Conservation: Mass is neither created nor destroyed in an ordinary chemical or physical process
Law of Conservation of Mass = Balanced Equations
Same number of elements on both sides of equation

5. Balancing Chemical Equations
Use coefficients in front of the compound to balance.
NEVER change the subscripts, though you need to use them to balance the equation.
Always use whole #’s
3CO(g) + Fe2O3(s)  2Fe(s) + 3CO2(g)
3 carbons 3 carbons
6 oxygen 6 oxygen
2 iron 2 Iron

6. Practice 2
KNO3  KNO O2 2
CaC2 + O2  Ca + CO2 2 2

7. Writing Chemical Equations
Start with the Reactants
End with the Products
An arrow separates to reactants and products
Use a ‘+’ to separate one or more reactants or products
Balance the equation
If the equation does not balance, check your formulas

8. Writing Chemical Reactions
Apply the physical state symbol to each compound
Solid = s
Liquid = l
Gas = g
Aqueous = aq
Is a solid dissolved in water
Know Diatomic elements, elements that are paired when not in a compound
Br2 I2 N2 Cl2 H2 O2 F2

9. aluminum reacts with iodine to form aluminum iodide
Practice
zinc reacts with iron (III) chloride to form iron and zinc (II) chloride 3 Zn + 2
FeCl3 2 Fe + 3
ZnCl2
aluminum reacts with iodine to form aluminum iodide
2 Al + 3 I2  2 AlI3