1. Evidence & Types of Chemical Reactions GPS 2a & 2b

2. Click for Bill Nye Video Part I: Describing Chemical Reactions
the process by which one or more substances are changed into one or more different substances.
in any chemical reaction, the original substances are known as the reactants and the resulting substances are known as the products.
steel wool oxygen (reacting) rust
Fe O Fe2O3
reactants product
Click for
Bill Nye Video

3. total mass of reactants = total mass of products
Part I: Describing Chemical Reactions
according to the law of conservation of mass:
total mass of reactants = total mass of products
g Fe g O g Fe2O3
chemical reactions are described by chemical equations.
chemical equation = represents, with symbols and formulas, the identities and molar amounts of the reactants and products in a chemical reaction.

4. Click Image for Cool Video
Example of a chemical equation for the breakdown of ammonium dichromate.
“The reactant ammonium dichromate yields the products nitrogen, chromium (III) oxide, and water.” is the same as:
(NH4)2Cr2O7(s)  N2(g) + Cr2O3(s) + H2O(g)
[This equation is UNBALANCED. We will balance it using coefficients later.]
Click Image for Cool Video

5. Check out this “cool” reaction!
Part II: Evidence of Chemical Reactions
To know for certain that a reaction has taken place requires evidence that one or more substances have undergone a change in identity.
Evolution of heat and light. A change in matter that releases energy as both heat and light is strong evidence that a chemical reaction has taken place. An example would be the decomposition you just viewed.
Temperature Change. If a reaction gets hot, we say it is exothermic (releasing heat energy to the environment). However, a reaction can absorb energy from the environment (get cold); this is called an endothermic reaction.
Check out this “cool” reaction!

6. Try this one for yourself!
3. Production of a gas. The evolution of gas bubbles when two substances are mixed is often evidence of a chemical reaction.
Ex: bubbles of CO2 gas form immediately when baking soda is mixed with vinegar; the classic middle school volcano experiment.
(baking soda) (vinegar) (carbon dioxide)
NaHCO3(s) + CH3COOH(l)  CO2(g) + NaC2H3O2(aq) + H2O(l)
Try this one for yourself!
(Click the image
to watch the video.)

7. Another video: This one you can’t try at home.
4. Formation of a precipitate. Many reactions take place between substances that are dissolved in liquids. If a solid appears after two solutions are mixed, a reaction has likely occurred. This solid is called a precipitate.
precipitate = a solid that is produced as a result of a chemical reaction in
solution & it separates from the solution.
Another video:
This one you can’t try at home.
The precipitate, lead iodide,
is toxic but still used
in the paint that lines
the roads we travel.

8. Check out these awesome color-changing reactions!
Color change. A change in color is often an indication of a chemical reaction. Ex: Bleach breaks down dye molecules attached to fabric, altering the wavelength of light they reflect, thus changing the color.
Evolution of an odor. Odors that suddenly appear indicate new, aromatic chemicals have been produced. Examples would be synthesis of perfumes & flavorings. (Sorry, hard to demo this online! )
Check out these awesome color-changing reactions!

9. Part III: Types of Chemical Reactions
There are 5 distinct types of chemical reactions. Each has a general formula that
represents the types of substances that react within each type of reaction.
Synthesis
Decomposition
Single replacement
Double replacement
Combustion
The first 4 types of reactions often involve ionic compounds. It’s helpful to think of the cations (A and B) as boys and the anions (X and Y) as girls.

10. A + X  AX Making Salt Synthesis Explained!!
Synthesis = combines 2 small compounds or atoms into one larger compound
the “marriage” reaction
Ex: Na + Cl2  NaCl K + CO3  K2CO Al + O2  Al2O3
A + X  AX
Making Salt
Synthesis Explained!!

11. Watch this video!! AX  A + X hydrogen peroxide breaks down
2. Decomposition = splits 1 compound into 2 or more smaller compounds or atoms
the “divorce” reaction
Ex) NaCl  Na + Cl H2O2  H2O + O2
hydrogen peroxide breaks down
into water & oxygen gas
AX  A + X
Watch this video!!

12. Click image to watch video
3. Single replacement = Replaces the cation or anion of a compound with another free cation or anion; the “one-cheater” reaction.
Ex) Cation Replacement
NaCl + K  KCl + Na Al2(CO3)3 + Li  Li2CO3 + Al
AgNO Cu  Ag Cu(NO3)2
AX + B  BX + A
Click image to watch video
of this reaction.

13. Watch the video of these reactions.
Ex) Single Replacement Rxns
Anion Replacement
NaBr + Cl2  NaCl + Br2 NaI + Cl2  NaCl + I2
AX + Y  AY + X
Watch the video of
these reactions.

14. What is the yellow stuff? You’ve seen this one before!
Double replacement = the cation of one compound is combined with anion of the other compound, creating 2 new compounds
the “switching partners” reaction
are often precipitation reactions
Ex: NaCl + KBr  NaBr + KCl Li2S + TiF2  LiF + TiS
Sn3P4 + Zn(NO3)2  Zn3P2 + Sn(NO3)4
AX + BY  AY + BX
What is the yellow stuff?
You’ve seen this one before!

15. Burn, baby, burn! CnHn + O2  CO2 + H2O
Combustion = Hydrocarbon + O2 produces CO2/CO, H2O plus energy
This reactions “involves hydrocarbons” reaction (not ionic compounds)
Sometimes results in CO2 as a product, other times CO
Ex) C2H6 + O2  CO2 + H2O C7H14 + O2  CO2 + H2O
C10H22 + O2  CO2 + H2O C7H14 + O2  CO + H2O
CnHn + O2  CO2 + H2O
Some of these demos could be classified as synthesis also. Watch closely & see if you can find them in the video!
Burn, baby, burn!

16. For more help with types of reactions, watch the tutorial below:
Tutorial Lesson
More Demos!

17. NaHCO3 (s) + CH3COOH(l)  CO2 + NaC2H3O2(aq) + H2O(l)Li Rb K Ba Sr Ca Na Mg Al Mn Zn Cr Fe Cd
let’s take a closer look at the single-replacement reaction...
the activity series helps determine whether or not one element can replace another in a single-replacement rxtn.
if an element is above another, it can replace it.
so, can these reactions happen or not?
Ex: NaCl + K  KCl + Na
Al2(CO3)3 + Li  Li2CO3 + Al
NaCl + Br2  NaBr + Cl2
Part IV: Symbols Found in Chemical Equations Co Ni Sn Pb H2 Sb Bi Cu Hg Ag Pt Au F2
Cl2
Br2 I2
NaHCO3 (s) + CH3COOH(l)  CO2 + NaC2H3O2(aq) + H2O(l)
 (s) 
 (g) 
(l)
2 atm
(aq)
0°C 
MnO2

18. NaHCO3 (s) + CH3COOH(l)  CO2 + NaC2H3O2(aq) + H2O(l)
Part IV: Symbols Found in Chemical Equations
Part V: Other Info About Chemical Reactions
some elements occur only in diatomic form, meaning they are bonded to another atom of that element. H2 N2 O2 F2 Cl2 Br2 I2
these gases are never found by themselves in any chemical formula or equation!!!
NaHCO3 (s) + CH3COOH(l)  CO2 + NaC2H3O2(aq) + H2O(l)
 (s) 
 (g) 
(l)
2 atm
(aq)
0°C 
MnO2
solid ( for precipitate)
gas ( for gaseous product)
liquid
in aqueous solution
yields or produces
reversible reaction
heat applied to reactants
specific pressure for rxtn
specific temp for reaction
catalyst needed for rxtn