f) Explain why alkenes often burn with a smoky flame, whereas the corresponding alkanes do not. Answer: Alkenes are more reactive than alkanes, as a result of the presence of a carbon double bond.
Why are alkenes more reactive than alkanes?
Alkenes are unsaturated, meaning they contain a double bond . This bond is why the alkenes are more reactive than the alkanes .
Why does alkenes produce a Sootier flame than alkanes?
Well, alkenes clearly have stronger C-C bonds in the olefin. And both alkenes, and long-chain alkanes TEND to combust incompletely. And thus there is more opportunity for the genesis of particulate carbon, as soot, and carbon monoxide.
Why do alkenes have a higher boiling point than alkanes?
The more intermolecular mass is added, the higher the boiling point. Intermolecular forces of alkenes gets stronger with increase in the size of the molecules. In each case, the alkene has a boiling point which is a small number of degrees lower than the corresponding alkane.
How is the combustion of alkenes different to combustion of alkanes?
Alkenes combust, but they are less likely than alkanes to combust completely. Complete combustion of alkenes produces carbon dioxide and water, provided there is a plentiful supply of oxygen. Incomplete combustion of alkenes occurs where oxygen is limited and produces water, carbon monoxide and carbon (soot).
35 related questions foundDo alkenes burn with a smoky flame?
Like the alkanes , the alkenes undergo combustion . However, alkenes are less likely to combust completely , so they tend to burn in air with a smoky flame due to incomplete combustion .
Why the flame of burning of alkenes is more luminous and smoky?
Alkenes tend to burn with sooty, luminous (yellow) flames. This is because the presence of the double bond reduces the amount of hydrogen in the molecule. This means that it will contain a greater proportion of carbon compared to a saturated molecule.
Why are alkenes more soluble than alkanes?
Alkenes are more soluble in water than alkanes because the carbon to carbon double bond contains a pi bond.
Are alkenes stronger than alkanes?
Alkenes are relatively stable compounds, but are more reactive than alkanes because of the reactivity of the carbon–carbon π-bond. Most reactions of alkenes involve additions to this π bond, forming new single bonds.
Why do alkenes have higher boiling points?
With a higher number of carbon atoms in the compound, the intermolecular forces increase in strength, causing an increase in the molecules' overall size. It also creates a change in respective Van Der Waals dispersion forces and thus contributes to the higher boiling point temperature in higher alkenes.
Why are alkenes not burned as fuels?
Alkenes readily burn, just like alkanes, to give carbon dioxide and water if combustion is complete e.g. However, they are NOT used as fuels for two reasons. They are far too valuable for use to make plastics, anti–freeze and numerous other useful compounds.
Do alkenes undergo combustion?
Alkanes and alkenes both undergo complete combustion , but only alkenes can undergo addition reactions .
Why alkenes are not used as fuels?
Alkenes are not used as fuels because: They are scarce in nature. They are made from other hydrocarbons to make plastics, anti–freeze and many other useful compounds. They burn with a smoky flame due to less efficient, and more polluting incomplete combustion, so the heat energy release is lower than for alkanes.
Why are alkenes less stable than alkanes?
Alkanes have a single bond, less energy than alkenes and alkynes which have respectively two and three bonds and higher energy. Higher energy means shorter bonds which means stronger bonds. But in this case, the stronger bonds in alkenes/alkynes have higher bond energy and thus more unstable than alkanes.
How do alkanes and alkenes differ in their molecular structures?
While alkanes and alkenes are both hydrocarbons, the primary difference is that alkanes are saturated molecules, containing only single covalent bonds (σ-bonds) between the carbon atoms whereas alkenes are unsaturated molecules containing a double covalent bond (combination of a π-bond and a σ-bond).
What are the differences between alkanes and alkenes?
The alkanes are saturated hydrocarbons—that is, hydrocarbons that contain only single bonds. Alkenes contain one or more carbon-carbon double bonds.
Are alkanes flammable?
Lower alkanes in particular are highly flammable and form explosive mixtures (methane, benzene) with air (oxygen). Solubility of alkanes in water is very low.
Are more substituted alkenes more reactive?
Relative stability of alkenes can be measured by using heats of hydrogenation upon reduction to the related alkane. More substituted alkenes are more stable than less substituted. Alkenes with the largest groups trans are more stable than cis.
Do alkenes have higher melting points than alkanes?
Melting points of alkenes depends on the packaging of the molecules. Alkenes have similar melting points to that of alkanes, however, in cis isomers molecules are package in a U-bending shape, therefore, will display a lower melting points to that of the trans isomers.
Why are there more possible isomers of an alkene than an alkane with the same number of carbon atoms?
The difference between these isomers depends on whether the methyl groups are on the same side (cis) of the double bond, or on opposite sides (trans). The presence of a double bond therefore will result in a significantly greater number of isomers as compared with the analogous alkane.
Are alkanes and alkenes miscible?
Solubility of Alkene
Alkanes and alkenes are non-polar molecules. Water, on the other hand, is a polar molecule. So, alkanes and alkenes are not soluble in water.
Why do alkanes burn with blue flame and alkene with yellow flame?
This is because when we move from alkane to alkyne, the percentage of carbon increases in a molecule. More carbon require more oxygen to burn. If the oxygen dies not increase, the burning will not be complete and we get yellow coloured flame and smoke.
Why does alkane burn with a blue flame?
Solution : Alkanes generally burn with blue flame or clean flame because the combustion is complete and no unburnt carbon particles are released.
Why do alkane burn with blue or clean flame?
Alkanes are saturated hydrocarbons which always burn with a clean blue flame because complete combustion takes place insufficient oxygen to give CO2 and H2O with the liberation of a large amount of heat and light.
