13.3 Reactions of alkenes Flashcards
Why are alkenes more reactive than alkanes?
-The 𝛑 bond is weaker than the σ bond and therefore bonds break more readily, as 𝛑 bonds have a lower enthalpy than σ bonds
-Due to the presence of a 𝛑 bond, the 𝛑 electrons are on the outside of the double bond so the electrons are more exposed than the electrons on the σ bond.
What reactions do alkenes undergo?
Addition reactions
What are the conditions for the hydrogenation of alkenes
Mixed with hydrogen, passed over a nickel catalyst at 423K
What is the product of hydrogenation of alkenes?
Alkane
What is the equation for hydrogenation of propene
What is the equation for hydrogenation of butan-1,3-diene
What is the reaction and conditions for halogenation of alkenes to form dihaloalkanes?
-Addition reaction with halogens (Br2, Cl2), room temperature
What is the equation for the addition reaction of propene with bromine?
What is the test for unsaturation (C=C)
Bromine water test, bromine water is added drop wise to sample
What is the positive result of the bromine water test?
-If C=C present, bromine water will decolourise from orange to colourless
-If no C=C, there will be no colour change, no addition reaction and solution will remain orange
What are the conditions for the reaction of alkenes with halogen halides?
-Alkenes react with gaseous hydrogen halides
-Room temperature and pressure
What are the products of the reaction of alkenes with halogen halides?
Haloalkanes
How is an addition reaction of alkenes with hydrogen halides different is the alkene is a gas or a liquid?
Gas - reaction takes place when the gases are mixed
Liquid - hydrogen halide is bubbled through
What is the equation for the reaction of propene with HCl?
For addition reactions of alkenes with hydrogen halides, why can there two products formed?
If the alkene is unsymmetrical, there will be two different isomers of the haloalkane produced
What are the conditions for the hydration of alkenes?
Steam (H2Og), H3PO4 catalyst
What is the product for the reaction of alkenes with water (hydration)
Alcohol
What is the equation for the reaction of propene with water? (hydration)
When is the hydration of alkenes used?
In the industry to produce ethanol from ethene
Why are there two different productions for the hydration of alkenes?
There are 2 different atoms being added across the double bond
