Chemistry_Grade_10-12 (1).pdf

C 2 h 4 h 2 o ch 3 ch 2 oh a catalyst is needed for

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C 2 H 4 + H 2 O CH 3 CH 2 OH A catalyst is needed for this reaction to take place. The catalyst that is most commonly used is phosphoric acid. 15.3.2 Elimination reactions An elimination reaction occurs when a reactant is broken up into two products. The general form of the equation is as follows: A B + C The examples below will help to explain this: 1. The dehydration of an alcohol is one example. Two hydrogen atoms and one oxygen atom are eliminated and a molecule of water is formed as a second product in the reaction, along with an alkene. CH 3 CH 2 OH CH 2 CH 2 + H 2 O H C H H C H OH H H H C C H H + H O H H 2. The elimination of potassium bromide from a bromoalkane . CH 3 CH 2 Br + KOH CH 2 CH 2 + KBr + H 2 O H C H H C Br H H+ KOH C H H C H H + KBr + H 2 O 281
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15.3 CHAPTER 15. TYPES OF REACTIONS - GRADE 11 3. Ethane cracking is an important industrial process used by SASOL and other petrochemical industries. Hydrogen is eliminated from ethane (C 2 H 6 ) to produce an alkene called ethene (C 2 H 4 ). Ethene is then used to produce other products such as polyethylene. You will learn more about these compounds in chapter 23. The equation for the cracking of ethane looks like this: C 2 H 6 C 2 H 4 + H 2 15.3.3 Substitution reactions A substitution reaction occurs when an exchange of reactants takes place. The initial reactants are transformed or ’swopped around’ to give a final product. A simple example of a reaction like this is shown below: AB + CD AC + BD Some simple examples of substitution reactions are shown below: CH 4 + Cl 2 CH 3 Cl + HCl In this example, a chorine atom and a hydrogen atom are exchanged to create a new product. Cu ( H 2 O ) 2+ 4 + 4 Cl Cu ( Cl ) 2 4 + 4 H 2 O Exercise: Addition, substitution and elimination reactions 1. Refer to the diagram below and then answer the questions that follow: (i) H C H H C Cl H H+ KOH C H H C H H + KCl + H 2 O (a) Is this reaction an example of substitution, elimination or addition? (b) Give a reason for your answer above. (c) What type of compound is the reactant marked (i)? 2. The following diagram shows the reactants in an addition reaction. C H H C H H + HCl (a) Draw the final product in this reaction. (b) What is the chemical formula of the product? 3. The following reaction takes place: 282
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CHAPTER 15. TYPES OF REACTIONS - GRADE 11 15.4 H C H H C OH H H H 2 SO 4 C H H C H H + H 2 O Is this reaction a substitution, addition or dehydration reaction? Give a reason for your answer. 4. Consider the following reaction: Ca(OH) 2 (s) + 2NH 4 Cl(s) CaCl 2 (s) + 2NH 3 (g) + 2H 2 O(g) Which one of the following best describes the type of reaction which takes place? (a) Redox reaction (b) Acid-base reaction (c) Dehydration reaction 15.4 Summary There are many different types of reactions that can take place. These include acid-base, acid-carbonate, redox, addition, substitution and elimination reactions.
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