Chemistry | Y10 Alkenes Flashcards
Why are alkenes unsaturated?
Alkenes are unsaturated because they have a double carbon-carbon bond.
Alkanes have a what type bond?
Alkenes Have a C=C Double Bond
Alkenes burn with what type of flame?
Alkenes Burn With a Smoky Flame
What are alkenes?
Alkenes are hydrocarbons which have a double bond between two of the carbon atoms in their chain.
Why does akenes having a double carbon bond make them unsaturated?
They have C=C double bond means that alkenes have two fewer hydrogens compared with alkanes containing the same number of carbon atoms. This makes them unsaturated.
How do the alkenes get reactive because of the double bond?
The C=C double bond can open up to make a single bond, allowing the two carbon atoms to bond with other atoms. This makes alkenes reactive.
The first four alkenes:
are ethene (with two carbon atoms),
propene (three Cs), butene (four Cs) and pentene (five Cs).
far more reactive than alkanes.
In a large amount of oxygen what do alkenes produce when burned?
In a large amount of oxygen, alkenes combust completely to produce only water and carbon dioxide
________ -chain alkenes have _____ as many hydrogen atoms as ___
Straight-chain alkenes have twice as
many hydrogen atoms as carbon
If there isn’t enough air for alkenes to burn (which happens usually) what happens?
There isn’t enough oxygen in the air for this, so when you burn them they tend to undergo incomplete combustion. Carbon dioxide and water are still produced, but you can also get carbon and carbon monoxide (CO) which is a poisonous gas.
What can incomplete combustion result in?
Incomplete combustion results in a smoky yellow flame, and less energy being released compared to complete combustion of the same compound
An example of an equation for incomplete combustion:
C4H8 +502 → 2CO + 2CO2 + 4H2O
Alkenes React via ____ Reactions
Addition of Hydrogen is Known as ___________
Alkenes React via Addition Reactions
Addition of Hydrogen is Known as Hydrogenation
What is a functional group?
A functional group is a group of atoms in a molecule that determine how that molecule typically reacts
Why do all alkenes have a function group?
All alkenes have the functional group ‘C=C’, so they all react in similar ways so you can suggest the products of a reaction based on your knowledge of how alkenes react in general.
What happens when alkenes react via addition reactions.
The carbon-carbon double bond will open up to leave a single bond and a new atom is added to each carbon:
Steam can React with Alkenes to Form ________
Steam can React with Alkenes to Form Alcohols
Hydrogen can react with what to become an equivalent, saturated alkane?
Hydrogen can react with the double-bonded carbons to open up the double bond and form the equivalent, saturated, alkane.
The alkene is reacted with hydrogen in the presence of a catalyst:
How is alcohol formed when steam is in contact with an alkene?
When alkenes react with steam, water is added across the double bond and an alcohol is formed.
How can ethanol be made using an alkene?
2) For example, ethanol can be made by mixing ethene with steam and then passing it over a catalyst
The conversion of ethene to ethanol is one way of
making ________ industrially.
The conversion of ethene to ethanol is one way of
making ethanol industrially.
What happens after the conversion of ethene to ethanol?
After the reaction has taken place, the reaction mixture is passed from the reactor into a condenser. Ethanol and water have a higher boiling point than ethene, so both condense whilst any unreacted ethene gas is recycled back into the reactor. The alcohol can then be purified from the mixture by fractional distillation.
Can Halogens can React with Alkenes?
Halogens can React with Alkenes
When alkenes react with metals like halogens what happens??
The molecules formed are saturated,
with the C=C carbons each becoming
bonded to a halogen atom.
