1. Balancing, States of Matter, and Writing
CHEMICAL REACTIONS
Balancing, States of Matter, and Writing

2. Evidence for A Chemical Reaction
Five Signs of a Chemical Change
Gas Given Off (Bubbles)
Color Change (BIGGIE!!!!!!)
Heat is Produced or Absorbed
Odor Change
Precipitate Forms (Solid is Made)

3. Chemical Equations
Chemical Equations are used to represent chemical reactions.
Reactants  Products
Law of Conservation of Matter (Mass) States: “Matter cannot be created or destroyed during a chemical reaction.”
We must balance chemical reactions (add coefficients) to comply with the law.

4. Chemical Equations (Cont)
Example:
CH4 + O2  CO2 + H2O
Methane + Oxygen  Carbon + Water
Dioxide
Reactants Products
1 – C 1 – C
4 – H 2 – H
2 – O 3 – O

5. Warm Up Name all the compounds and find their masses.
Cu + AgNO3 ---> Ag + Cu(NO3)2

6. Balancing
Chemical reactions change the groupings of the atoms, but DO NOT create or destroy atoms, so there must be the same number of each type of atom on each side of the arrow. We must use coefficients to Balance a Chemical Equation

7. Balancing Chemical Equations
Determine the correct formula for each reactant and product by supplying the subscripts to the formulas.
Once you write the correct formula, DO NOT change the subscripts.
Add coefficients in front of balanced formulas to give the same number and kind of atoms on both sides.
Use the lowest possible ratio of coefficients.

8. Example
CH4 + 2 O2  CO2 + 2 H2O
If I place a 2 in front of the O2 and the H2O, then I end up with:
Reactants Products
1 – C 1 – C
4 – H 4 – H
4 – O 4 – O

9. You Try this One C2H4 + O2  CO2 + H2O 2 – C - 1 4 – H - 2 2 – O - 3

10. Another Example C3H6 + O2  CO2 + H2O 3 – C - 1 6 – H - 2 2 – O - 3

11. Warm Up What would the coefficients be for this reaction:
PCl5 + H2O  H3PO4 + HCl
1, 4, 1, 5

12. Physical States Symbols in parentheses after each formula: Example:
Solid (s)
Liquid (l)
Gas (g)
Aqueous (aq)
Aqueous means dissolved in water.
Example:
2 H2O2 (aq)  2 H2O (l) + O2 (g)

13. Word Equations
Chemical Equations written out as words. This is a statement that describes the chemical equation in place of using symbols.
Steps:
Using the words, write the correct formulas in the correct locations.
Add the states of matter abreviations.
Balance the equation.

14. Words to watch for
States of matter – This is a symbol that is used to identify the state of matter for each substance in a reaction.
Gas, Liquid, Solid, Aqueous
Gas (g)
Liquid (l)
Solid (s) may also be called a Precipitant (ppt) or a crystal (c)
Aqueous (aq) means dissolved in water.

15. Example 1 Zn(s) + 2 HCl (aq)  ZnCl2 (aq) + H2(g)
Solid Zinc reacts with Hydrochloric Acid to produce Zinc II Chloride and Hydrogen gas.
Zinc + Hydrochloric Acid  Zinc Chloride + Hydrogen
Zn (s) + HCl (aq)  ZnCl2 (aq) + H2 (g)
Zn(s) HCl (aq)  ZnCl2 (aq) + H2(g)

16. You Try This One
Solid Calcium Oxide reacts with solid Aluminum to produce solid Aluminium Oxide and Calcium.
calcium oxide + aluminum → aluminum oxide + calcium
CaO (s) + Al (s)  Al2O3 (s) + Ca (s)
3CaO (s) + 2Al (s)  Al2O3 (s) + 3Ca (s)

17. Example 2
Aqueous Lead (II) Nitrate reacts with aqueous Sodium Sulfate to produce aqueous Sodium Nitrate and solid Lead (II) Sulfate.
Lead (II) Nitrate + Sodium Sulfate  Sodium Nitrate + Lead (II) Sulfate
Pb(NO3)2 (aq) + Na2SO4 (aq) → NaNO3 (aq) + PbSO4 (s)
Pb(NO3)2 (aq) + Na2SO4 (aq) → 2 NaNO3 (aq) + PbSO4 (s)

18. You Try This One Na3PO4 + CuSO4 → Na2SO4 + Cu3(PO4)2
Sodium Phosphate and Copper (II) Sulfate react in water to produce aqueous Sodium Sulfate and solid Copper (II) Phosphate.
sodium phosphate + copper (II) sulfate → sodium sulfate + copper (II) phosphate
Na3PO4 + CuSO4 → Na2SO4 + Cu3(PO4)2

19. Types of Reactions
There are many kinds of chemical reactions that occur. Some are very simple while others are very complex and may occur in multiple steps.
A number of reactions conform to some relatively simple patterns
Understanding and identifying these patterns can be helpful in predicting the products of similar reactions

20. Types of Reactions 1. Combustion 2. Synthesis 3. Decomposition
4. Single Replacement
5. Double Replacement
Acid - Base

21. Combustion
A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning they produce heat.
C10H8 + 12 O2 ---> 10 CO2 + 4 H2O

22. Synthesis
A synthesis reaction is when two or more simple compounds combine to form a more complicated one.
General Form:
A + B ---> AB
Combination of iron and sulfur to form iron (II) sulfide:
8 Fe + S8 ---> 8 FeS

23. Decomposition
A decomposition reaction is the opposite of a synthesis reaction - a complex molecule breaks down to make simpler ones.
General form:
AB ---> A + B
2 H2O ---> 2 H2 + O2

24. Single Replacement
This is when one element trades places with another element in a compound.
General form:
A + BC ---> AC + B
Mg + 2 H2O ---> Mg(OH)2 + H2

25. Double Replacement
This is when the anions and cations of two different molecules switch places, forming two entirely different compounds.
General form:
AB + CD ---> AD + CB
Pb(NO3)2 + 2 KI ---> PbI2 + 2 KNO3

26. Acid - Base
This is a special kind of double displacement reaction that takes place when an acid and base react with each other. General Form:
HA + BOH ---> H2O + BA
HBr + NaOH ---> NaBr + H2O