Chemistry lecture 11

Chemical reaction

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A chemical reaction or is a reaction of two or more chemicals (reagents), yielding a chemical change and a product(s). A chemical change is defined as molecules attaching to each other to form larger molecules, molecules breaking apart to form two or more smaller molecules, or rearrangement of atoms within molecules. Chemical reactions usually involve the making or breaking of chemical bonds.

Types

There are six types of common chemical reactions. Most reactions will be classified as one of these, though there may be others that cannot be classified:

• Synthesis
• Also called composition or direct combination.
• Two or more individual atoms, ions, or molecules coming together and forming a new substance.
• Only one product.
• Example: A + B → AB

What Is a Synthesis Reaction?

A synthesis reaction or direct combination reaction is a type of chemical reaction in which two or more simple substances combine to form a more complex product. The reactants may be elements or compounds. The product is always a compound.

• Decomposition
• Also called analysis
• A chemical compound breaks apart into two or more individual atoms, ions, or molecules.
• Only one reactant.
• Example: AB → A + B
• Combustion
• A specific type of decomposition, involving large amounts of light and heat. Combustion reactions typically involve carbon, hydrogen, and oxygen (the reactants) forming carbon dioxide (CO₂) and water (H₂O) (the products).
• Example: C_xH_x + O₂ → CO₂ + H₂O
• Single displacement
• Also called single replacement.
• One compound and one element are displaced.
• One compound and one element on both sides.
• Example: AB + C → AC + B
• Double displacement
• Also called double replacement, metathesis, or ion exchange
• Two compounds are displaced.
• Two compounds on both sides.
• Example: AB + CD → AC + BD
• Neutralization
• Also called water-forming reactions.

A specific type of double displacement reactions involving an acid and a base (reactants) neutralizing (canceling each other out) to form water.
-Acid-base reactions involve transfer of protons /a hydrogen ion H⁺/from one molecule (acid) to another (base). Here, acids act as proton donors and bases as acceptors.

• In a rearrangement reaction, the atoms and bonds within a molecule rearrange to form an isomer of the original compound.

A-B=C → A=B-C

-         In an oxidation-reduction reaction (also known as a redox reaction), one reactant loses electrons (that is, it is oxidized), and the other reactant gains electrons (it is reduced). The oxidized reactant is the reducing agent and the reduced reactant is the oxidizing agent.  Example: A + B → A⁺ + B^-

  Single displacement reactions are typically also redox reactions.

A chemical reaction does not change the nucleus of the atom in any way, only the interaction of the electron clouds of the involved atoms. (Changes in the composition of the nuclei of atoms are called nuclear reactions, and are not considered chemical reactions, although chemical reactions may follow a nuclear transformation.)