Part I: Describing Chemical Reactions chemical reaction 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 2 Fe 2 O 3 reactants product

“The reactant ammonium dichromate yields the products nitrogen, chromium (III) oxide, and water.” is the same as: (NH 4 ) 2 Cr 2 O 7 (s)  N 2 (g) + Cr 2 O 3 (s) + H 2 O (g) [This equation is UNBALANCED. We will balance it using coefficients later.] Example of a chemical equation for the breakdown of ammonium dichromate.

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 CO 2 gas form immediately when baking soda is mixed with vinegar; the classic middle school volcano experiment. (baking soda) (vinegar) (carbon dioxide) NaHCO 3 (s) + CH 3 COOH (l)  CO 2 (g) + NaC 2 H 3 O 2 (aq) + H 2 O (l)

5.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. 6.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! )

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. 1.Synthesis 2.Decomposition 3.Single replacement 4.Double replacement 5.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.

1.Synthesis = combines 2 small compounds or atoms into one larger compound the “marriage” reaction Ex: Na + Cl 2  NaCl K + CO 3  K 2 CO 3 Al + O 2  Al 2 O 3 A + X  AX

2. Decomposition = splits 1 compound into 2 or more smaller compounds or atoms the “divorce” reaction Ex) NaCl  Na + Cl 2 H 2 O 2  H 2 O + O 2 hydrogen peroxide breaks down into water & oxygen gas AX  A + X

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 Al 2 (CO 3 ) 3 + Li  Li 2 CO 3 + Al AgNO 3 + Cu  Ag + Cu(NO 3 ) 2 AX + B  BX + A

Ex) Single Replacement Rxns Anion Replacement NaBr + Cl 2  NaCl + Br 2 NaI + Cl 2  NaCl + I 2 AX + Y  AY + X

4.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 Li 2 S + TiF 2  LiF + TiS Sn 3 P 4 + Zn(NO 3 ) 2  Zn 3 P 2 + Sn(NO 3 ) 4 AX + BY  AY + BX

5.Combustion = Hydrocarbon + O 2 produces CO 2 /CO, H 2 O plus energy This reactions “involves hydrocarbons” reaction (not ionic compounds) Sometimes results in CO 2 as a product, other times CO Ex) C 2 H 6 + O 2  CO 2 + H 2 O C 7 H 14 + O 2  CO 2 + H 2 O C 10 H 22 + O 2  CO 2 + H 2 O C 7 H 14 + O 2  CO + H 2 O C n H n + O 2  CO 2 + H 2 O Some of these demos could be classified as synthesis also. Watch closely & see if you can find them in the video!

For more help with types of reactions, watch the tutorial below:

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 Al 2 (CO 3 ) 3 + Li  Li 2 CO 3 + Al NaCl + Br 2  NaBr + Cl 2 Part IV: Symbols Found in Chemical Equations Li Rb K Ba Sr Ca Na Mg Al Mn Zn Cr Fe Cd Co Ni Sn Pb H 2 Sb Bi Cu Hg Ag Pt Au F 2 Cl 2 Br 2 I 2  (s) (s)   (g) (g)  (l)(l) 2 atm (aq) 0°C  MnO 2 NaHCO 3 (s) + CH 3 COOH (l)  CO 2  + NaC 2 H 3 O 2 (aq) + H 2 O (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. H 2 N 2 O 2 F 2 Cl 2 Br 2 I 2  these gases are never found by themselves in any chemical formula or equation!!!  (s) (s)   (g) (g)  (l)(l) 2 atm (aq) 0°C  MnO 2 NaHCO 3 (s) + CH 3 COOH (l)  CO 2  + NaC 2 H 3 O 2 (aq) + H 2 O (l) 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