2.4 Types of Chemical Reactions

Synthesis

Synthesis reactions are also known as formation reactions.

Definition: A synthesis reaction is when two or more reactants (usually elements) join to form a compound.

• A + B --> AB where A and B represent elements

The elements may form ionic compounds, like these:

• Sodium metal and chlorine gas combine to form sodium chloride.

• Magnesium metal reacts with oxygen gas to form magnesium oxide.

Or the elements may form covalent compounds, like this:

• Nitrogen gas and oxygen gas join to form dinitrogen monoxide.

Decomposition

Decomposition reactions are the opposite of synthesis reactions. Definition:A decomposition reaction is when compounds breaks down into two or more products (often elements).

• AB --> A + B where A and B represent elements

Ionic compounds may decompose to produce elements, like this:

• Table salt, sodium chloride, can be broken down into sodium metal and chlorine gas by melting salt at 800ºC and running electricity through it.

Covalent compounds may decompose into elements, like this:

• By running electricity through water, the water molecules decompose into hydrogen and oxygen gases.

Watch this video on decomposition reactions.

Single Replacement

• A + BC --> B + AC where A is a metal, or
• A + BC --> C + BA where A is a non-metal

• Aluminum foil in a solution of copper (II) chloride produces solid copper and aluminum chloride.

• When fluorine is bubbled through a sodium iodide solution, iodine and sodium fluoride are produced.

Here is a video to further explain single displacement reactions, it is a two part video.

Double Replacement

Double replacement reactions swap elements between two compounds reacting together to form two new compounds.

• Two elements switch partners

• When potassium chromate and silver nitrate react, they switch partners to form silver chromate and potassium nitrate.

Watch this video to learn more about double displacement.

Neutralization

• Acid + base --> salt + water
• HX + MOH --> MX + H₂O where X and M are elements or polyatomic ions

• Sulphuric acid is used to neutralize calcium hydroxide:

• Phosphoric acid helps to neutralize the compounds that cause rust, such as iron (II) hydroxide.

Watch this video on neutralization reactions.

Combustion

Combustion reactions occur when a compound or element react with oxygen to release energy and produce an oxide.

• C_XH_Y + O₂ >--> CO₂ + H₂O where X and Y represent integers

• Natural gas (methane) is burned in furnaces to heat homes.

• An acetylene torch is used to weld metals together

• Carbohydrates like glucose combine with oxygen in our body to release energy.

Balancing Combustion Reactions

Video Summary

Summary of Reactions

Click here for a review sheet of Types of Reactions.

Chemical Reactions Review

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Practice Quiz

Click on these links for practise naming reactions, completing reactions and balancing reactions.  For the 1st 1/2, predict what the reactants were based on the products.  For the second 1/2, predict the products based on the reactants.  Refer back to your notes, lessons and vidoes on reaction types.

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Practice Quiz - Multiple Choice

Complete this quiz to help you prepare for your assignments and the Chemistry Test.