Organic- Alkanes Flashcards
Reaction and which catalyst is used?
How can alkanes be produced from alkenes?
By hydrogenation: heating alkenes with hydrogen gas in the presence of a Pt or Ni catalyst.
What role does the Pt/Ni catalyst play in hydrogenation?
It increases the surface area, enhancing the reaction rate.
Write the reaction for the hydrogenation of butene.
Butene + H₂ → (with Pt/Ni catalyst and heat) → Butane
C4H8 + H2–pt/Ni–>C4H10
What is the purpose of hydrogenation in the manufacture of margarine?
Hydrogenation is used to convert vegetable oils (unsaturated) into margarine by raising the melting point, turning it from liquid to soft solid.
What is cracking?
Cracking is the process of breaking down larger, less useful hydrocarbons into smaller, more useful alkanes and alkenes by heating with a catalyst (Al₂O₃).
What are the conditions for cracking?
High temperature and passing over an aluminium oxide (Al₂O₃) catalyst, with no oxygen to prevent combustion.
* Crack aloe*
Why is cracking used?
Cracking is used to produce alkanes and alkenes of lower relative molecular mass (Mr) from heavier crude oil fractions, which are in higher demand.
What is complete combustion of alkanes?
Complete combustion occurs in excess oxygen, where alkanes are fully oxidized to form carbon dioxide (CO₂) and water (H₂O).
incomplete combustion of alkanes?
occurs in limited oxygen, forming carbon monoxide (CO) and possibly carbon (soot), along with water (H₂O).
Why is carbon monoxide dangerous?
Carbon monoxide binds to haemoglobin in the blood, preventing oxygen transport, causing dizziness, unconsciousness, and possibly death.
What is free-radical substitution in alkanes?
hydrogen atom in an alkane is replaced by a halogen (Cl₂ or Br₂) in the presence of ultraviolet light (UV).
steps of the free-radical substitution mechanism?
Initiation: UV light breaks Cl-Cl or Br-Br bond to form free radicals.
Propagation: Free radicals react with alkanes to form new radicals and products.
Termination: Two radicals combine to form a stable molecule, ending the reaction.
Why is free-radical substitution not ideal for producing specific halogenoalkanes?
It produces a mixture of products because multiple substitutions can occur.
Why are alkanes unreactive?
- Alkanes have strong C-H and C-C bonds, requiring high energy to break.
- they are nonpolar, meaning they don’t react with polar reagents like nucleophiles or electrophiles.
What pollutants are formed from the combustion of alkanes in car engines?
Carbon monoxide (CO), oxides of nitrogen (NO/NO₂), and volatile organic compounds (VOCs).
How do nitrogen oxides contribute to pollution?
Nitrogen oxides can form acid rain, which harms plant and aquatic life, and contributes to photochemical smog.
What is the role of a catalytic converter in reducing pollution?
A catalytic converter reduces pollutants by-
1. oxidizing CO to CO2: 2CO+O2→2CO 2
2. reducing NO/NO₂ to N₂: 2CO+2NO→2CO2+N2
3. oxidizing unburnt hydrocarbons: CnH2n+2+(3n+1)[O]→nCO 2+(n+1)H2O.
2. tiko and tino went to see tiko’s parents (2) in newzealnd
Why is cracking used to obtain useful compounds?
Cracking produces smaller alkanes and alkenes of lower Mr, which are in higher demand as fuels and feedstocks for chemical industry processes (like polymerization).
What is the role of ultraviolet light in free-radical substitution?
UV light provides the energy needed to break halogen bonds (Cl-Cl or Br-Br), initiating the formation of free radicals.
Why are alkanes nonpolar molecules?
Carbon and hydrogen share electrons almost equally due to their similar electronegativities, resulting in no partial charges (δ+ or δ-).
What type of bond fission occurs during initiation in free-radical substitution?
Homolytic fission, where each atom gets one electron from the bond.
What type of bonding is present in alkanes?
covalent bonds between carbon and hydrogen atoms, with single bonds (sigma bonds) between carbon atoms
Why are C-H and C-C bonds in alkanes strong?
C-H and C-C bonds are strong due to the overlap of orbitals and the relatively low reactivity of the bonds.
What types of isomerism do alkanes exhibit?
Alkanes show structural isomerism, where the carbon chain can be arranged in different ways (e.g., branching).
