1. Forming new substances
Ch 6 – Chemical Reactions
Forming new substances

2. Matter and Change
Changes in matter can be described in terms of physical changes and chemical changes
Physical property – characteristic of a substance that can be observed w/out changing the substance into another substance
Color, hardness, texture, shine, flexibility, conducting heat and electricity
Chemical property – characteristic of a substance that describes its ability to change into another substance
Flammability, rust, reactivity

3. Physical change – any change that alters the form or appearance of a substance (can get back what you started with) Chemical change – change in matter that produces one or more new substances Chemical changes occur when bonds break and new bonds form

4. Chemical Reactions
Involve changes in properties and changes in energy that you can observe.

5. Evidence to a Chemical Rxn
Gas formation
Solid formation – called a precipitate
Color change
Temperature/Energy change (heat)
Light is emitted
Change in smell or taste

6. Chemical Formulas
Shorthand way of using chemical symbols and numbers to represent a compound or group of elements.
Shows the number of atoms of each element present in the formula.

7. i.e. - chemical formula for water = H2O
tells us that it is composed of 2 hydrogen atoms and 1 oxygen atom
Ex.
O C6H12O6 Na2SO4

8. The small numbers are referred to as subscripts
Common Prefixes:
Mono = 1 Di = 2
Tri = 3 Tetra=4
Penta = 5 Hexa= 6
Hepta = 7 Octa = 8
Nona = 9 Deca = 10

9. Writing Formulas Covalent compounds made of 2 nonmetals
CO2 = Carbon “di” oxide
N2O = Dinitrogen monoxide
N3O5 = ??

10. Ionic compounds made with a metal and a non-metal
The compounds overall charge = zero
NaCl = Sodium chloride
(Na is a +ion and Cl is a –ion)
MgCl2 = Magnesium chloride
(Mg is a 2+ion, so we need 2 –ions of Cl)

11. Hydrogen + Oxygen Yields Water
Chemical Equation
Description of a chemical reaction using chemical formulas and symbols
i.e. H2 + O2 → H2O
Hydrogen Oxygen Yields Water

12. Equation Terms Reactants starting materials & ALWAYS on left Products
formed materials & ALWAYS on right
Coefficient
a number placed in front of a chemical symbol or formula ( a regular size number )
Used to BALANCE equations, has distributed propery

13. C + O2 → CO2 Carbon + Oxygen Yields Carbon dioxide REACTANTS PRODUCTS
Example of Coefficient:
3CO2 - the “3” is the coefficient

14. Law of Conservation of Matter
Matter is neither created nor destroyed in ordinary chemical/physical changes

15. Balancing Chemical Equations
A chemical equation must show the same number of each type of atom on both sides of the equation.
Steps to Balance an Equation
Write the equation
Count the atoms
Use coefficients to balance atoms
Look back and check

16. change H2O to 2H2O makes products H=4, O=2 H2 + O2 → 2H2O then
1. Write the equation
H O2 → H2O
Count the atoms
Reactants Products
H = 2, O = 2 H = 2, O = 1
Use Coefficients to balance atoms
change H2O to 2H2O makes products H=4, O=2
H O2 → 2H2O then
change H2 to 2H2 makes reactants H=4,O=2
2H2 + O2 → 2H2O
Look Back and Check
Reactants: H=4, O=2 Products: H=4, O=2
Balanced Equation 

17. 4 Types of Chemical Rxns Synthesis Decomposition Single Replacement
Double Replacement

18. 1. Synthesis Rxn
Two or more substances combine to form a single compound.
*To Put together*
2Na Cl → NaCl

19. → +

20. 2. Decomposition *To Take Apart*
A single compound breaks down to form two or more simpler substances.
H2CO3 → H2O CO2

21. → +

22. 3. Single Replacement Rxn
An element takes the place of another element that is part of a compound.
Zn HCl → ZnCl H2

23. + → +

24. 4. Double Replacement Rxn
Ions in two compounds switch places.
NaCl + AgNO3 → NaNO3 + AgCl

25. → + +

26. Law of Conservation of Energy
Energy can neither be created nor destroyed
Every rxn involves energy

27. Energy & Reactions
There is a “certain” amount of energy required to make substances react.
This is called the - Activation Energy

28. Exothermic Rxn
A rxn in which energy is “released” or “removed”. (Exit = to leave, etc)
Energy can be released as: Light, Heat, or Electrical energy
2Na + Cl2 → 2NaCl + energy

29. Endothermic Rxn
A chemical rxn in which energy is “absorbed” or enters the rxn. (Enter = to come in)
2H2O + energy → 2H O2

30. Factors that affect Rates of Rxn
1. Temperature
Increase temp = increase rxn
Decrease temp = decrease rxn
2. Concentration
3. Surface area
Inc SA = Inc rxn

31. Substance that speeds up a rxn Lowers the Activation Energy
4. Catalyst
Substance that speeds up a rxn
Lowers the Activation Energy
Biological catalyst is called an enzyme
Inhibitor
slows down or stops rxn (i.e. preservatives and poison)