1. Chapter 12 Chemical Reactions

2. Forming New Substances
Chemical Reaction- a process in which one or more substances change to make one or more new substances
The chemical and physical properties of the new substance differ from those of the original substances.
Examples of chemical changes:
Changing colors of leaves
baking muffins

3. Signs of a Chemical Reaction
Gas bubbles
energy change
color change
formation of a solid precipitate
precipitate- Solid substance that is formed in a solution

4. Signs of a Chemical Reaction
A change of properties:
The signs can help you identify a chemical reaction, but they do not guarantee a reaction took place.
Ex. Boiling water gives off gas, but this is a physical change.
The most important sign that a chemical change took place is the formation of new substances that have different properties.

5. Chemical Bond
Chemical bond- force that holds two atoms together in a molecule. The original bonds must break and new bonds must be formed.
Ex 1: H2 and Cl2
Chlorine gas has a greenish-yellow color
Hydrogen gas is flammable
Hydrogen chloride is a nonflammable, colorless gas.
Ex 2: Na and Cl2
Na is a metal that reacts violently with water
Cl is a greenish-yellow poisonous gas
Sodium chloride is a harmless substance that almost everyone uses.

6. Ch 14.2 Chemical Formulas and Equations
Chemical Formulas- a shorthand way to use chemical symbols and numbers to represent a substance. It shows how many atoms of each kind ore present in a molecule.

7. Chemical Formulas and Equations
Subscript- number written below and to the right of a chemical symbol in a formula.
*If no subscript is present, it means only 1 atom of that element is present.
Ex: H2O H = O =
C6H12O6 C = H= O=
CO2 C = O =

8. Writing formulas for Covalent Compounds
composed of 2 nonmetals
use prefixes
if there is only one atom of the first element
drop the mono- prefix
change 2nd elements suffix to –ide
Ex: CO2
N2O
Mono
Hexa Di
Hepta
Tri
Octa
Tetra
Nona
Penta
Deca

9. Writing formulas for Ionic Compounds
composed of a metal and a nonmetal
put the metal first, nonmetal second overall charge must be 0.
charges of the ions will cancel out
criss-cross rule
change suffix of nonmetal to –ide
Ex: NaCl
MgCl2

10. Chemical Equations
Chemical Equations-Uses chemical symbols and formulas as a shortcut to describe a chemical reaction
Reactants-the starting materials in a chemical reaction
Products-the substance formed from a reaction
Ex: C + O2  CO2
reactant product

11. How do new substances form in a chemical reaction?
1. Original bonds must break
Molecules are always moving
If molecules bump into each other with enough energy, the chemical bonds in the molecules break.
2. Atoms rearrange
3. New bonds must form

12. The Reason Equations Must be Balanced:
                                    
The Reason Equations Must be Balanced:
·Atoms are never lost or gained in a chemical reaction
·They are just rearranged
·The # of atoms in the reactants must = # of atoms in the products
This is called balancing the reaction

13. Law of Conservation of Mass
Law of Conservation of Mass- Mass is neither created or destroyed in ordinary chemical and physical changes

14. How to Balance an Equation:
You must use coefficients- number placed in front of a chemical symbol or formula
Ex 1: 2CO means 2 carbon monoxide molecules
Ex 2: 2H2O means 2 dihydrogen monoxide molecules
Total there are 4 hydrogen atoms and 2 oxygen atoms
·Only coefficients are changed when balancing equations – never subscripts!!
___H ___O2  ___H2O |

15. Balancing Chemical Reactions
____ Na + ____Cl2 → ____NaCl
Na Na
Cl Cl
____ N2 + ­­_____ H2 → ____ NH3
N N
H H

16. Balancing Chemical Reactions
____ Na2S+ ____AlCl3 → ____NaCl + ____ Al2S3 Na Na S S Al Al Cl Cl

17. Balancing Chemical Reactions
____ Ca+ ____O2 → ____CaO Ca Ca O O ____ CaCl2+ ____Li2S → ____CaS + ____ LiCl Cl Cl Li Li S S

18.                                
Types of Reactions
Synthesis Reaction- A reaction in which two or more substances combine to form one new compound.
A + B = AB
Ex: Sodium + Chlorine  Sodium Chloride
2Na + Cl2  2NaCl

19. Synthesis Reaction

20. Types of Reactions
Decomposition Reaction- A reaction in which a single compound breaks down to form two or more simpler substances.
AB = A + B
Ex: Carbonic Acid = Water and carbon Dioxide
H2CO3  H2O + CO2

21. Decomposition Reaction

22.                                                             
                                                         
                                                            
                                                            
                                                            
Types of Reactions
Single Replacement - A single element replaces another element that is part of a compound.
Products are a new compound and a different single element
A + BC  AC + B
Ex: Zn + 2HCl  ZnCl2 + H2
*The more reactive element can displace a less reactive element.
Ex: Copper can replace Silver, but the opposite can’t occur.

23. Single Replacement

24.                                 
Types of Reactions
Double Replacement Reaction- A reaction in which ions from two compounds switch places.
AB + CD = AD + CB
Ex.
Sodium Chloride + Silver Fluoride  Sodium Fluoride + Silver Chloride
NaCl + AgF  NaF + AgCl

25. Double Replacement

26. 14.4 Energy and Rates of Chemical Reactions
                                   
                                   
14.4 Energy and Rates of Chemical Reactions
Exothermic Reaction- Reaction in which energy is released.
EXO means “goes out” or “exits”
Ex: 2Na + Cl2 2NaCl + energy
Endothermic Reaction A reaction in which energy is taken in
ENDO means “goes in”
Ex: 2H2O + energy  2H2 + O2

27. Law of Conservation of Energy
Law of Conservation of Energy- Energy cannot be created or destroyed
Energy can be transferred from one object to another
Rate of Reaction- the speed at which new particles form
Activation Energy-The initial boost of energy. The smallest amount of energy that molecules need to react.

28. Factors that Affect Reaction Rate
Temperature – the higher the temperature, the faster the reaction rate
Concentration- The higher the concentration of reactants, the faster the reaction rate
Surface Area- (amount of exposed surface on a substance) The larger the surface area, the faster the reaction rate
Inhibitor- A substance that slows down a reaction. Ex: Preservatives in food slow down bacteria growth.
Catalyst- A substance that speeds up a reaction without being permanently changed. NOT A REACTANT!! Ex: Enzymes speed up reactions in your body.