1. Chemical Equations and Reactions

2. Describing Chemical Reactions
A chemical reaction is the process by which one or more substances are changed into one or more different substances.
Reactants are the original substances
Products are the resulting or new substances
Law of Conservation of mass states, the total mass of reactants must equal the total mass of products for any given chemical reaction.
Chemical equations represent, with symbols and formulas, the identities and relative molecular or molar amounts of the reactants and products in a chemical reaction

3. Symbols used in chemical equations

4. Symbols used in chemical equations (cont.)

5. Symbols used in chemical equations (cont.)

6. Indications of a Chemical Reaction
Evolution of energy as heat and light
Production of a gas (bubbling)
Formation of a precipitate
A solid that is produced as a result of a chemical reaction in solution and that separates from the solution.
Color change

7. Characteristics of Chemical Equations
All properly written chemical equations will share these characteristics
The equation must represent known facts.
All reactants and products must be identified
The equation must contain the correct formulas for the reactants and products.
Watch out for HOFBrINCl’s
The law of conservation of mass must be satisfied.
Atoms are never created or destroyed in a chemical reaction.
Atoms on the reactant side must equal atoms on the product side.
Coefficients are used to “balance” all the atoms in a chemical equation. They are inserted in front of a chemical formula and act as a multiplier.

8. Types of Chemical Reactions
Categorizing chemical reactions into different types helps us to predict the products which will occur during reaction
There are 5 basic types of Reactions we will discuss:
Synthesis
Decomposition
Single displacement (replacement)
Double displacment (replacement)
Combustion

9. Synthesis Reaction Also known as a composition reaction
Two or more substances react to form a new compound
A + B  AB
2Mg(s) + O2(g)  2MgO(s)

10. Decomposition Reactions
A single compound undergoes a reaction that produces two or more simplier substances.
AB  A + B
2H2O  2H2 + O2
CaCO3  CaO + CO2

11. Combustion Reactions
A substance combines with oxygen and produces a combination of water and carbon dioxide. Usually involves hydrocarbons
CxHy + O2  CO2 + H2O
C3H8 + 5O2  3CO2 + 4H2O

12. Single Displacement Reactions
One element in a compound replaces another element in a different compound
A + BC  AC + B
2Al + 3Pb(NO3)2  3Pb + 2Al(NO3)3

13. Single Displacement Reactions (cont.)
Not all single displacement reaction will take place.
Must refer to the activity series of metals to predict whether the metal is “strong” enough to displace the other metal.

14. In order for a single displacement reaction to take place the lone metal must be higher on the activity series than the metal in the compound.

15. Double Displacement Reactions
The ions of two compounds exchange places to form two new compounds
AB + CD  AD + CB
2KI + Pb(NO3)2  PbI2 + 2KNO3