Alkenes are manufactured by cracking larger alkane molecules. When one molecule of dodecane, $$$\mathrm{C}_{12} \mathrm{H}_{26}$$$, is cracked, three molecules of but-1-ene and one other product are formed. (i) Use molecular formulae to complete the symbol equation for this reaction. $$\[ \mathrm{C}_{12} \mathrm{H}_{26} \rightarrow \]$$ ................................... $$$+$$$ ................................... (ii) Suggest the type of chemical reaction which happens during cracking. ...................................................................................................................................

Chemistry

IGCSE&ALevel

CAIE

Exam No：0620_w24_qp_42. Year：2024 Question No：5(c)

Answer:

Knowledge points:

11.4.1. State that the bonding in alkanes is single covalent and that alkanes are saturated hydrocarbons

11.4.2. Describe the properties of alkanes as being generally unreactive, except in terms of combustion and substitution by chlorine

11.4.3. State that in a substitution reaction one atom or group of atoms is replaced by another atom or group of atoms

11.4.4. Describe the substitution reaction of alkanes with chlorine as a photochemical reaction, with ultraviolet light providing the activation energy, Ea, and draw the structural or displayed formulae of the products, limited to monosubstitution

11.5.1. State that the bonding in alkenes includes a double carbon–carbon covalent bond and that alkenes are unsaturated hydrocarbons

11.5.2. Describe the manufacture of alkenes and hydrogen by the cracking of larger alkane molecules using a high temperature and a catalyst

11.5.3. Describe the reasons for the cracking of larger alkane molecules

11.5.4. Describe the test to distinguish between saturated and unsaturated hydrocarbons by their reaction with aqueous bromine

11.5.5. State that in an addition reaction only one product is formed

11.5.6.1. bromine or aqueous bromine

11.5.6.2. hydrogen in the presence of a nickel catalyst

11.5.6.3. steam in the presence of an acid catalyst and draw the structural or displayed formulae of the products

Answer:

Knowledge points:

Solution:

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