DF 6 Flashcards
What alkenes are gases?
Ethene, propane and butene
What alkenes are liquids?
Ones with 5-14 carbons
What alkenes are solid?
ones with 15 or more carbons
General formula of alkenes
CnH2n
What is a electrophile?
Species attracted to negative charge
What type of bonds does the double bond in an alkene contain?
One sigma and one pi bond
What is a carbocation?
An ion with a positively charged carbon atom
What does benzene look like?
Hexagon with a circle in the middle
Example of a name of an alkene with 2 double bonds
PentA -1,4- DIene
Which type of bond breaks first?
The pi bond as it has a lower enthalpy than the sigma bond
How is the pi bond formed?
Formed below and above the plane of the carbon atoms
by a sideways overlap of P orbitals
explain why some alkenes can have E or Z isomers
the pi-bond fixes the carbon atoms in position
preventing rotation around the double bond
explain why the bond angles in alkenes are 120o
there are 3 regions of charge on each carbon in the double bond
these will repel each other as far as possible to minimise repulsions
forming a trigonal planar shape
explain why alkenes are attacked by electrophiles
Because they contain a double bond which is an area of high electron density due to the orbital overlap
explain why alkenes undergo addition reactions
they are able to donate an electron pair to an electrophile
Which breaks the pi-bond
and add a small molecule to form a new product molecule
explain why ethene is a planar molecule
each carbon of the double bond has a trigonal planar shape
these are fixed in place by the pi bond
Which prevents rotation
Reagents needed for the reaction of propene and bromine
Propane and bromine water with no special conditions
Reagents needed for the reaction of propene and hydrogen
Propene gas, hydrogen gas, 150 degrees Celsius, Nickel catalyst
Why are catalyst used in industry?
- Speeding up the process
- Reducing the amount of energy required
- improving percentage yield
How does catalyst poisoning occur?
- Poisoned molecules are more strongly ADsorbed than the reactants
- Poisoned molecules ADsorb onto the catalyst surface but do not react
- No space for reactants to attach to the surface
- catalyst becomes inactive
What are homogenous catalysts?
catalyst which are in the same physical state as the reactant
How to draw enthalpy diagram for adding a catalyst?
Large curve - Ea - without catalyst
Small curve - Ec - with catalyst
Describe what happens in an ethene + hydrogen reaction with a catalyst
- Hydrogen adsorbs onto the catalyst surface
- ethen adsorbs onto the catalyst surface
- Double bond in ethene weakens then breaks
- allowing new bonds with hydrogen to be formed
- the newly formed at hand is released from the surface and diffuses away
