Chemistry_Grade_10-12 (1).pdf

1 substitution reactions substitution reactions

Info icon This preview shows pages 177–180. Sign up to view the full content.

View Full Document Right Arrow Icon
1. Substitution reactions Substitution reactions involve the removal of a hydrogen atom which is replaced by an atom of another element, such as a halogen (F, Cl, Br or I) (figure 9.11). The product is called a halo-alkane . Since alkanes are not very reactive, heat or light are needed for this 163
Image of page 177

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
9.7 CHAPTER 9. ORGANIC MOLECULES - GRADE 12 H C H C H H + HBr H C H C H Br H H Figure 9.11: A substitution reaction reaction to take place. e.g. CH 2 =CH 2 + HBr CH 3 -CH 2 -Br (halo-alkane) Halo-alkanes (also sometimes called alkyl halides ) that contain methane and chlorine are substances that can be used as anaesthetics during operations. One example is trichloromethane, also known as ’chloroform’ (figure 9.12). C Cl H Cl Cl CHCl 3 Figure 9.12: Trichloromethane 2. Elimination reactions Saturated compounds can also undergo elimination reactions to become unsaturated (fig- ure 9.13). In the example below, an atom of hydrogen and chlorine are eliminated from the original compound to form an unsaturated halo-alkene. e.g. CH 2 Cl CH 2 Cl CH 2 = CHCl + HCl H C H C H Cl Cl H H C H C H Cl + HCl Figure 9.13: An elimination reaction 3. Oxidation reactions When alkanes are burnt in air, they react with the oxygen in air and heat is produced. This is called an oxidation or combustion reaction. Carbon dioxide and water are given off as products. Heat is also released during the reaction. The burning of alkanes provides most of the energy that is used by man. e.g. CH 4 + 2 O 2 CO 2 + 2 H 2 O + heat Exercise: The Alkanes 164
Image of page 178
CHAPTER 9. ORGANIC MOLECULES - GRADE 12 9.7 1. Give the IUPAC name for each of the following alkanes: (a) C 6 H 14 (b) C H H H C C C C H H H H H H H H H (c) CH 3 CH 3 2. Give the structural formula for each of the following compounds: (a) octane (b) 3-methyl-hexane 3. Methane is one of the simplest alkanes and yet it is an important fuel source. Methane occurs naturally in wetlands, natural gas and permafrost. However, methane can also be produced when organic wastes (e.g. animal manure and decaying material) are broken down by bacteria under conditions that are anaer- obic (there is no oxygen). The simplified reaction is shown below: Organic matter Simple organic acids Biogas The organic matter could be carbohydrates, proteins or fats which are broken down by acid-forming bacteria into simple organic acids such as acetic acid or formic acid. Methane-forming bacteria then convert these acids into biogases such as methane and ammonia. The production of methane in this way is very important because methane can be used as a fuel source. One of the advantages of methane over other fuels like coal, is that it produces more energy but with lower carbon dioxide emissions. The problem however, is that methane itself is a greenhouse gas and has a much higher global warming potential than carbon dioxide. So, producing methane may in fact have an even more dangerous impact on the environment.
Image of page 179

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 180
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern