3.0 Organic Chemistry 1

3.1.2 Cracking of alkanes

Questions 3.1.2(a)

1. In ordinary language, what does it mean to crack something?
2. Why is it sometimes necessary to crack a substance?
3. How does the burning of butane (a smaller alkane) compare with the burning of kerosene (a mixture of longer alkanes)? Refer to Figure 3.1(a).
4. Large objects such as rocks can be cracked using a sledge hammer or power grinder. Suggest how the invisible alkane molecules may be cracked (Hint: Kinetic property, movement and collision)

Answers to Questions 3.1.2(a)

Cracking of alkanes is achieved by heating them to high temperatures (400-800 ^oC). Sometimes a catalyst is added to speed up the process.

NB: In cracking, the simpler alkanes produced are accompanied by products other than alkanes. They normally include alkenes and hydrogen gas. Some smaller molecules recombine.

Questions 3.1.2(b)

Complete the equation that follows; hence identify the simpler alkane (formula and name) produced in the cracking of propane.

NB: Like in all other chemical equations, the number of atoms of each element on the left must balance those on the right.

Answers to Questions 3.1.2(b)