CHAPTER 8. TYPES OFREACTIONS 8.3
Chapter 8 — Summary
See the summary presentation ( Presentation: VPjvj at http://www.everythingscience.co.za)- There are many different types of reactions that can take place. These include acid-base, acid-
carbonate, redox, addition, substitution and elimination reactions. - The Arrhenius definition of acids andbases defines an acid as a substance that increases the
concentration of hydrogen ions (H+or H 3 O+) in a solution. A base isa substance that increases
the concentration of hydroxide ions (OH−) in a solution. However this definition only applies
to substances that are inwater. - The Bronsted-Lowry definition is a much broader one. An acid is a substance that donates
protons and a base is a substance that accepts protons. - In different reactions, certain substances can act as both an acid and abase. These substances
are called ampholytes and are said to be amphoteric. Water is an example of an ampholyte. - A conjugate acid-base pair refers to two compounds in a reaction (one reactant and one product)
that transform or changeinto the other through the loss or gain of a proton. - When an acid and a base react, they form a salt and water. The salt is made up of a cation from
the base and an anion from the acid. An example of a salt is sodium chloride (NaCl), which is
the product of the reaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl). - The reaction betweenan acid and a base is a neutralisation reaction.
- Titrations are reactions between an acid and a base that are used to calculate theconcentration
of one of the reacting substances. The concentration of the other reacting substance must be
known. - In an acid-carbonate reaction, an acid and a carbonate react to form a salt, carbon dioxide and
water. - A redox reaction is one where there is always a change in the oxidation numbers of the elements
that are involved in thereaction. - Oxidation is the loss of electrons and reduction is the gain of electrons.
- When two or more reactants combine to forma product that containsall the atoms that were
in the reactants, then this is an addition reaction. Examples of additionreactions include the
reaction between etheneand bromine, polymerisation reactions and hydrogenation reactions. - A reaction where the reactant is broken down into one or more product,is called an elimination
reaction. Alcohol dehydration and ethane cracking are examples of eliminationreactions. - A substitution reaction is one where the reactants are transformed or swopped around to form
the final product.
Chapter 8 End of Chapter Exercises
- Give one word/termfor each of the followingdescriptions:
(a) A chemical reactionduring which electronsare transferred
(b) The addition of hydrogen across a double bond
(c) The removal of hydrogen and halogen atoms from an alkane to forman alkene