16th October 2019

chemgapedia

9

What is the main use of alkenes?

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They are used as starting materials in the syntheses of alcohols, plastics, laquers, detergents, and fuels. The most important alkenes for the chemical industry are ethene, propene and 1,3-butadiene. Ethene is the most important organic feedstock in the chemical industry.

What are alkanes and alkenes?

Hydrocarbons are compounds made from carbon and hydrogen atoms joined by covalent bonds. Alkanes are saturated - they have only single bonds. Alkenes have a double bond - they are unsaturated. Alkenes react with brown bromine water and decolourise it, but alkanes do not.

What is the test for an alkene?

Testing for alkenes. Bromine water is used to tell the difference between an alkane and an alkene. An alkene will turn brown bromine water colourless as it reacts with the double bond. Bromine water remains brown in the presence of an alkane as there is no double bond.

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What are the physical properties of alkenes?

Physical Properties of Alkenes

Structural Isomerism.
Geometric (cis-trans) Isomerism.
Physical state.
Density.
Solubility.
Boiling Points.
Melting Points.
Polarity.

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What is the functional group of the alkenes?

Alkenes and alkynes. The functional group in the alkenes is the carbon-to-carbon double bond. The functional group in the alkynes is the carbon-to-carbon triple bond.

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Why is there no Methene?

Alkenes are similar to alkanes. The main difference between them is that alkenes have a carbon to carbon double bond. Methene is not possible as alkenes require a carbon-carbon double bond and methane only has one carbon atom.

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Why are alkenes are unsaturated?

Alkenes are called unsaturated molecules because two atoms can join onto half of the carbon = carbon double bond when it opens up. In other words they potentially have spare bonds to link up with other atoms and alkanes cannot do this.

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Why are alkenes are more reactive than alkanes?

Yes, alkenes are more reactive. This is due to the properties of the carbon-carbon bond. In alkanes there is a single bond, denoted as . At first thought, it seems that double must be stronger than single but in fact, due to the nature of the bond, it is more reactive than a -bond.

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What is meant by cracking in chemistry?

In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors.

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Which is more reactive an alkane or an alkene?

alkyne is more reactive than alkane and alkene because in alkyne is join each other with triple bond so it is no more stable than other two, so it is more reactive than alkane and alkene . However, alkanes have single bonds, alkenes have double bonds, and alkynes have triple bonds.

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What is the use of ethene?

Ethene (ethylene) is the most important organic chemical, by tonnage, that is manufactured. It is the building block for a vast range of chemicals from plastics to antifreeze solutions and solvents. Figure 1 On the site at Grangemouth in Scotland, ethene is produced by steam cracking of naphtha.

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Are alkenes saturated?

Hydrocarbons are compounds made from carbon and hydrogen atoms joined by covalent bonds. Alkanes are saturated - they have only single bonds. Alkenes have a double bond - they are unsaturated. Alkenes react with brown bromine water and decolourise it, but alkanes do not.

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Why are alkenes useful?

The presence of this double bond allows alkenes to react in ways that alkanes cannot. They can react with oxygen in the air, so they could be used as fuels. But they are more useful than that. They can be used to make ethanol - alcohol - and polymers - plastics - two crucial products in today's world.

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How do you test for alkenes?

Testing for alkenes. Bromine water is used to tell the difference between an alkane and an alkene. An alkene will turn brown bromine water colourless as it reacts with the double bond. Bromine water remains brown in the presence of an alkane as there is no double bond.

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How alkenes are made?

Fractions that are produced by the distillation of crude oil can go through a process called cracking, a chemical reaction which produces smaller hydrocarbons, including alkanes and alkenes. Ethene and other alkenes are unsaturated hydrocarbons and can be used to make polymers.

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What is the definition of general formula?

A general formula is a type of empirical formula that represents the composition of any member of an entire class of compounds.

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What are alkanes and what are they used for?

The organic compounds known as alkanes are used primarily as fuels, but their derivatives can be found in paints, plastics, cosmetics, cleaners and pharmaceuticals. The simplest alkanes are propane, methane, butane and ethane.

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Why do alkenes burn with a smoky flame?

It's smoky, indicating incomplete combustion due to the presence of C=C bonds, which appears as soot (carbon.) It will be black, due to the production of soot from incomplete combustion. Alkenes burn with a sooty flame to produce carbon dioxide, soot (carbon) and water.

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What is the special bond found in alkenes?

Alkenes. Alkenes are hydrocarbons that contain a carbon-carbon double bond. The number of hydrogen atoms in an alkene is double the number of carbon atoms. For example, the molecular formula of ethene is C₂H₄, while for propene it is C₃H₆.

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Are alkenes reactive?

Alkenes are relatively stable compounds, but are more reactive than alkanes, either because of the reactivity of the carbon–carbon pi-bond or the presence of allylic CH centers. Most reactions of alkenes involve additions to this pi bond, forming new single bonds.

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Can alkanes be used as fuel?

The alkanes are highly combustible and are valuable as clean fuels, burning to form water and carbon dioxide. Methane, ethane, propane and butane are gases and used directly as fuels. Alkanes from pentane up to around C₁₇H₃₆ are liquids. Gasoline is a mixture of alkanes from pentane up to about decane.

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What is Cycloalkane used for?

These uses are typically classified by the number of carbons in the cycloalkane ring. Many cycloalkanes are used in motor fuel, natural gas, petroleum gas, kerosene, diesel, and many other heavy oils. There are 4 general groups of cycloalkanes: Small rings (cyclopropane, cyclobutane)

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