11.5: Types of Chemical Reactions

Synthesis Reactions

A synthesis reaction is a reaction in which two or more reactants combine to form one product.

General Equation: R + S -> RS
Reactants: Generally, two elements, or two compounds (where at least one compound is a molecular compound)
Probable Products: A Single Compound

Watch the following video from 2:39 to 4:29 to view a synthesis reaction.

https://youtu.be/Y3kDZXP4_5A?t=159

Try predicting the products for the following synthesis reaction: O₂ + Mg ->

Watch the following video from 3:05 to 4:23 to view the answer.

https://youtu.be/MhlWTZwDHM8?t=184

Try predicting the products for the following synthesis reaction: Zn + S->
Watch the following video from 4:40 to 6:15 to view the answer.

https://youtu.be/MhlWTZwDHM8?t=279

Decomposition Reactions

A decomposition reaction is a reaction in which one reactant is broken down into two or more different products.

General Equation: RS -> R + S
Reactants: Generally, a single binary compound or a compound with a polyatomic ion.
- Note: Binary means a substance made of two different elements.
Probable Products: Two elements (for a binary compound), or two or more elements and/or compounds (for a compound with a polyatomic ion).

Watch the following video from 1:50 to 3:31 to view a decomposition reaction.

https://youtu.be/yS8noHTIJ_E?t=111

Normally, some type of energy is needed for a decomposition reaction to occur (heat, light or electricity).

Try predicting the products for the following decomposition reaction: H₂O->

Watch the following video from 0:29 to 1:30 to view the answer.

https://youtu.be/1ocQhkHw_MM?t=29

Try predicting the products for the following decomposition reaction: HgO->
Watch the following video to view the answer.

https://youtu.be/_Y1alDuXm6A

Combustion Reactions

A combustion reaction is a reaction that occurs when fuel (many times a hydrocarbon) and oxygen react to form products and energy (heat and light).

General Equation: C_xH_y + O₂ -> CO₂ + H₂O + energy (heat/light)
Reactants: Hydrocarbon and Oxygen
Probable Products: Carbon Dioxide and Water

Yulo1985, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

Watch the following video to learn about combustion reactions.

https://youtu.be/q3tf9OxBdYc

Write the chemical reaction for the complete combustion of methane CH₄.

Watch the following video from 3:37 to 4:23 to view the answer.

https://youtu.be/oeQTFpuC5Jc?t=217

Single-Displacement Reactions
(Single-Replacement Reactions)

A single-displacement reaction is a reaction in which one element is replaced by another, and the reactants are always one element and one compound.

General Equation: T + RS -> TS + R
Reactants: An element and a compound in a single displacement reaction, an element replaces another element from a compound. For a single-displacement reaction to occur, the element that is displaced must be less active than the element that is doing the displacing. To determine if the reaction will take place, you need to look at the activity series (metals) or the periodic table (halogens).
Probable Products: A different element and a new compound.
Note: Metals replace metals and nonmetals replace nonmetals.

Watch the following video from 1:00 to 2:26 to learn about single-displacement reactions.

https://youtu.be/qhmTXdOKTBo

When dealing with single-replacement reactions, a reaction may not occur. To see if a reaction will occur when looking at cations, we need to look at an "Activity Series of Metals." This list shows how reactive metals are in a single displacement reaction. The more reactive elements are more likely to react. So, a more reactive element will replace a less reactive element, but not the other way around. Take a look at the Activity Series of Metals to the right. This will help determine when a reaction will occur between cations.
Examples:

Na + KCl -> No Reaction
- There is no reaction because K is above Na on the Activity Series, so K will hang onto the Cl.
Na + CaS -> NaS + Ca
- This reaction takes place because Na is above Ca on the Activity Series, so Na will replace Ca.

https://www.jpl.nasa.gov/edu/teach/activity/spacecraft-materials-and-the-chemistry-of-space-exploration/

To determine if an anion will react, you need to look at the periodic table to see if a halogen will replace a different halogen. Activity decreases as you go down the halogen group on the periodic table.
Examples:

~ Br₂ + NaI -> NaBr + I₂ (This reaction takes place because Br is above I on the periodic table, so Br will replace I.)
~Br₂ + NaCl-> No Reaction (There is no reaction because Cl is higher up on the periodic table than Br, so Cl will hang onto Na. Once you determine if a reaction will take place, you will use the rules for forming Ionic Formulas to predict the new compound and element.)

Try predicting the products for the following single-displacement reaction: Cl₂ + NaBr->

Watch the following video from 2:55 to 3:27 to view the answer.

https://youtu.be/qhmTXdOKTBo?t=178

Try predicting the products for the following single-displacement reaction: CuCl₂ + Al->

Watch the following video from 3:49 t0 6:48 to view the answer.

https://youtu.be/qhmTXdOKTBo?t=224

Double-Displacement Reactions
(Double-Replacement Reactions)

A double-displacement reaction is a reaction in which two ionic compounds exchange ions to form two new ionic compounds.

General Equation: RS + TU -> RU + TS
Reactants: Two ionic compounds. Two ionic compounds react by exchanging cations to form two different compounds.
Probable Products: Two new compounds. Double replacement reactions are driven by the formation of a precipitate, a gaseous product, or water.

Watch the following video from 0:00 to 3:27 to learn about double-displacement reactions.

https://youtu.be/_oixjNeKtxs

Some double-displacement reactions will result in a gas as one of the products.
Some double-displacement reactions are neutralization reactions. This means and acid and base react to form a salt and water.
Some double-displacement reactions will result in a precipitate. A precipitate reaction is a reaction where an insoluble solid is formed during a reaction between two aqueous solutions.

Now, let's discuss how we can tell if a compound will be a solid (s) or aqueous (aq). To do this, a solubility table will be used. How do you use the solubility table?

I means not soluble = Solid (s)
- This is the precipitate
S means it is soluble in water = aqueous (aq)

If you have a compound, you will split the compound into its parts then see where they cross on the solubility table. For example:

AgBr has the following components:
- Ag+ and Br-
  - These two elements cross at I, so the compound AgBr is a solid.
AgF has the following components:
- Ag+ and F-
  - These two elements cross at S, so the compound is aqueous.