1. Chemical Reactions

2. Background
We learned about Physical and Chemical properties and changes.
Physical properties were those like mass, volume, density, melting point, boiling point, conductivity, malleability, state/phase of matter etc.
Changes within these properties can be undone and the properties of the substances are not altered.
Chemical properties were those like oxidation, flammability, and reactivity.
Changes within these properties CANNOT be undone. Change is permanent and the product now has new properties of its own.

3. Remember…..
Chemical Reactions occur because of the forces between atoms and valence electrons. The groups on the periodic tables all are organized based on Chemical and Physical Properties. Chemically, we are speaking of valence electrons.
IONIC BOND- When a metal bond to a NON-metal, this is usually due to an IONIC bond where the NON-metal has taken a free electron (valence electron) from a metal. If you look…groups 1 and 2 (all metals) have 1 or 2 valence electrons. The NON-metals are in groups They have between 3-8 valence electrons. They NEED the electrons to complete their “octets” (means 8 by the way) or shells. BY stealing away 1 or 2 from a Metal, they begin to complete their shells and leave the Metal’s shell full.
Covalent Bond- When a NON-metal and a NON-metal are close enough for electromagnetic force to attract valence electrons, the atoms SHARE electrons to complete their “octets” or shells. *See next slide.

4. Remember—we did Covalent in class!

5. Organize Your Thoughts
Chemical
reactions
Chemical
equations
Chemical
equations
To identify the reactants and products in a chemical equation.
To balance a chemical equation with coefficients.
To identify synthesis (combination), decomposition, and combustion reactions.
To identify single-replacement reactions.
To identify double-replacement reactions.
To predict the products of a reaction.
Synthesis
Decomposition
Single replacement
Double replacement
Combustion
Balancing equations
Predicting products
from reactants
Packard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page 175

6. Signs of Chemical Reactions when atoms bond….
There are five main signs that indicate a chemical reaction has taken place:
release
input
change in color
change in odor
production of new
gases or vapor
input or release
of energy
difficult to reverse

7. In other words……..

8. ubbles production of new gases or vapor change in odor
difficult to reverse
input or release
of energy
change in color
difficult to reverse

9. What? New Substance!?
I thought you said Matter cannot be created nor destroyed, only changed???
New substance is referring to a substance that has its own chemical properties (different from those that created it).
Example: Sometimes when 2 substances are mixed, the result is a PRECIPITATE. This is a SOLID that is the product of 2 reacting substances.
A kidney stone is a real life example! There
Aren’t really stones in your body!

10. Chemical Equations
Reactants – the substances that exist before a chemical change (or reaction) takes place.
Products – the new substance(s) that are formed during the chemical changes.
CHEMICAL EQUATION indicates the reactants and products of a reaction.
Objectives:
To identify seven elements that occur naturally as diatomic molecules, H2, N2, O2, F2, Cl2, Br2, I2. [HOBrFINCL twins or BrINClHOF brothers]
To write a chemical equation from the description of a chemical reaction.
REACTANTS  PRODUCTS
For Example H  2H20

11. Do you remember 6th Grade
Do you remember 6th Grade? Combine your 6th Grade Knowledge with your 8th Grade Knowledge….
Use these to fill in the Reactants and the Products

12. Did you get it correct?

13. Common Processes using a chemical equation:
Look! They are the reverse of each other!!!

14. Some Symbols Used in Chemical Equations
“Yields”; indicates result of reaction
Used to indicate a reversible reaction
A reactant or product in the solid state;
also used to indicate a precipitate
Alternative to (s), but used only to indicate a precipitate
A reactant or product in the liquid state
A reactant or product in an aqueous solution
(dissolved in water)
A reactant or product in the gaseous state
(s)
(l)
(aq)
(g)

15. Chemical Equations Reactants Product 4 Al(s) + 3 O2(g) 2 Al2O3(s)
aluminum oxide
Reactants
Product
4 Al(s) O2(g) Al2O3(s)
A chemical equation is an expression that gives the identities and quantities of the substances in a chemical reaction
Chemical formulas and other symbols are used to indicate the starting material(s) or reactant(s), which are written on the left side of the equation, and the final compound(s) or product(s), which are written on the right side. An arrow, read as yields or reacts to form, points from the reactants to the products.
Abbreviations are added in parentheses as subscripts to indicate the physical state of each species:—(s) for solid, (l) for liquid, (g) for gas, and (aq) for an aqueous solution.
A balanced chemical equation is when both the numbers of each type of atom and the total charge are the same on both sides. A chemical reaction represents a change in the distribution of atoms but not in the number of atoms.
The letters (s), (g), and (l) are the
physical states of compounds.
The numbers in the front are called
stoichiometric coefficients.

16. Characteristics of Chemical Equations
The equation must represent known facts.
The equation must contain the correct formulas for the reactants and products.
The law of conservation of mass must be satisfied. (Equation must be balanced).

17. 4 Al atoms + 3 O2 molecules yields 2 molecules of Al2O3
Chemical Equations
aluminum oxide
sandpaper
4 Al(s) O2(g) Al2O3(s)
This equation means:
4 Al atoms O2 molecules yields 2 molecules of Al2O3

18. Visualizing a Chemical Reaction2
Na Cl NaCl 2

19. Chemical Equations The Law of Conservation of Matter
Because the same atoms are present
in a reaction at the beginning (reactants)
and at the end (products), the amount
of matter in a system does not change.
The Law of Conservation of Matter
Law of Conservation of Matter means that nothing is “lost” or “stolen”. In the real world retail theft costs business lots (much of the theft is actually employee theft)!
20%
100%
Chemical
Factory
100%
80%
Kotz web

20. Chemical Equations
Because of the law of the conservation of matter,
an equation must be balanced.
It must have the same number of atoms of the same kind on both sides.
*Remember from class?
On both sides:
C = 1
H = 4
O = 4

21. Word Equations
A WORD EQUATION describes chemical change using the names of the reactants and products.
Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water.
methane oxygen
carbon dioxide water
Reactant
Product
CH4 + 2 O2
CO2 + 2
H2O

22. NEW! Very IMPORTANT!
*Synthesis (also known as Composition) and Decomposition reactions are considered REDOX reactions (more on this later)

23. Synthesis Reaction – Synthesis means put together!
2 Na Cl  NaCl Na Cl
Na+
Cl - Cl
Cl -
Na+ Na
General form: A B  AB
element or element or compound
compound compound

24. Synthesis Reactions Photosynthesis 6 CO2 + H2O C6H12O6 + O2 6 6
Formation of water 2
H O H2O 2
Formation of salt
A photomicrograph of common table salt © Carl J. Bowser, Department of Geology and Geophysics, University of Wisconsin, Madison 2
Na Cl NaCl 2
General Form
A B C

25. Decomposition Reaction – Decomposition means to breakdown!
2 H2O +
2 H2 O2 H H O O H + H O O H
General form: AB A + B
compound
two or more elements
or compounds

26. Decomposition Reactions
Hydrogen Peroxide 2
H2O H2O O2 2
Electrolysis of water
H2O H O2
electricity 2 2
Nitrogen triiodide 2
NI N I2 3
General Form
AB A B

27. Ionic bonds results in redox
*Both Synthesis and Decomposition reactions (explanations to follow) are considered Oxidation-Redox reactions. Think back to our last 2 days of bonding. The placement of electrons had to be altered in order for the molecules to form.
Oxidation (redox) is a type of chemical reaction in which electrons are transferred from one substance to another. For oxidation to occur, one substance must lose electrons and a second substance must gain the lost electrons.
The substance gaining electrons is said to be reduced and the substance losing the electrons is said to be oxidized. Thus an oxidation reaction is called a Redox reaction.
In the Redox Reaction diagram, sodium (Na) is being oxidized and chlorine (Cl) is being reduced.
The term "oxidation", with its obvious root from the word "oxygen", assumes that oxygen has an oxidation number of WHY -2?? BECAUSE Oxygen must gain 2 electrons in order to fill its shell remember?
Above, Sodium (Na) must LOSE 1 electron, so therefore its oxidation number is +1
Ionic bonds results in redox

28. Single and Double Replacement Reactions
Single-replacement reaction
Mg CuSO4  MgSO Cu
General form:
A BC  AC B
Double-replacement reaction
CaCO HCl  CaCl H2CO3
General form:
AB CD  AD CB

29. Acid-Base
Neutralization is a type of chemical reaction in which a strong acid and strong base react with each other to form water and salt. Have you ever been unlucky enough to be stung by a wasp or a bee? Bee stings are acidic in nature, which is why a household remedy for a bee sting is baking soda or sodium bicarbonate, which is a basic substance. A wasp sting, on the other hand, is mildly basic, so a household remedy for this will be vinegar, also known as acetic acid. These simple treatments ease these painful stings by a process called neutralization.
Heartburn, as well as an acidic stomach due to eating too much spicy food, can be relieved by taking an antacid. The antacid is alkaline/basic and helps neutralize the stomach's acidic environment. If you look at the medicine for heartburn in the picture below, you may have used this one before to ease your heartburn via the process of neutralization.
Evidence of an Acid-Base Reaction is that a SALT and WATER are the Products

30. Acid- Base Reaction

31. Combustion
Hydrocarbons (Carbon and Hydrogen combo) Combine to react and produce Carbon Dioxide and Water. Evidence of a combustion reaction are Carbon Dioxide and Water as products.