If there is a double bond in a hydrocarbon, one can imagine a reaction where an additional h atom is bonded to each of the c atoms joined by the double bond, which is turned into a single b. The combustion of hydrocarbons is accompanied by a release of energy and is a primary source of energy production in our society figure 16. Give two conditions needed for this reaction to take place properly. In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or longchain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carboncarbon bonds in the precursors. Phosphoric acid h3po4, high temperature of 300oc and 6070 atm pressure are needed as catalyst. Hydrocarbon is a class of organic chemical compounds composed only of the elements carbon c and hydrogen h. Double bonds are higher energy bonds in comparison to a single bond but not necessarily 2 fold higher.
Cracking is the name given to breaking up large hydrocarbon. The longest chain chosen for the root name must include both carbon atoms of the double bond. Cracking allows large hydrocarbon molecules to be broken down into. Depending on the type of central bond present, the hydrocarbon can be classified as an alkane single bond, alkene double bond, or alkyne triple bond. There are two good economic reasons for cracking oil fractions i there isn. Hydrocarbon, any of a class of organic chemical compounds composed only of the elements carbon c and hydrogen h. Relate what you observe to the carboncarbon double bond.
A hydrocarbon with a triple bond between carbons is an alkyne, and the simplest compound in this class is acetylene, c2h2. The conversion of highmolecularweight alkanes to lower ones is called cracking. Learn vocabulary, terms, and more with flashcards, games, and other study tools. The root chain must be numbered from the end nearest a double bond carbon atom. Cracking and alkenes crude oil, hydrocarbons and alkanes aqa. Note, that one of the products that is formed when we crack naphtha contains a double bond between two carbon atoms.
Every carbon atom must have 4 bonds, so draw a 2carbon molecules. The chain is numbered in the same way that alkanes, except that the carbon atoms of the double bond get the lowest possible numbers. How do you tell if a hydrocarbon has a double bond in its carbon skeleton. An alkene is a hydrocarbon containing double bonds. This answer has been confirmed as correct and helpful. Because carbon has 4 electrons in its outermost shell and because each covalent bond requires a donation of 1 electron, per atom, to the. This is achieved by using high pressures and temperatures without a catalyst, or lower temperatures and pressures in the presence of a catalyst. Based on the names for the butene molecules, propose a name for this molecule. Learn about crude oil, hydrocarbons and alkanes with bitesize gcse chemistry aqa. With five c atoms, we will use the pent stem, and with a cc double bond, this is an alkene, so this molecule is a pentene. Notice the long starting hydrocarbon is saturated no double bonds, some of the products are unsaturated.
Chapter 2 hydrocarbons a hydrocarbon molecule contains only carbon and hydrogen. As is true for all hydrocarbons, alkanes burn in air to produce carbon dioxide co2 and water h2o and release heat. Below ordinary circumstances some of the hydrocarbons are gases, others are liquids and still others are solids. The catalyst works by providing the hydrocarbon gases with a convenient surface for the cracking to take place. An unsaturated hydrocarbon with a double bond is called an.
Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarbyls. The answer to this is d, 2 has the shortest bond because it is a double bond, next 4 is a benzene ring, which is a resonance structure, which means that all the carbons technically have partial bonds between each other, or you can imagine the double bonds to be continuously rotating between. What are hydrocarbons that contain only single covalent. A hydrocarbon with single bonds only is called saturated. When a compound has more than one unsaturation, such as a double bond, the number of the carbon where the double bond originates is included in the name using a number. Heat, it needs to be a vapour and either high temperature for decomposition or any electric spark to break the bond.
Cracking is the name given to breaking up large hydrocarbon molecules into. An alkene molecule with one double bond contains 7 carbon atoms. In addition, hydrocarbons may differ in the types of carboncarbon bonds present. In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon 620 hydrocarbons are examples of group 14 hydrides. A hydrocarbon is an organic compound made of nothing more than carbons and hydrogens. All alkenes contain a double carbon bond, which is shown as two lines between. We begin counting at the end of the chain closest to the double bondin this case, from the leftthe double bond spans carbons 2 and 3, so the name becomes 2pentene. By far the most common reaction of hydrocarbons is combustion, which is the combination of a hydrocarbon with o 2 to make co 2 and h 2 o. An unsaturated hydrocarbon with a double bond is called an alkene. Cracking allows large hydrocarbon molecules to be broken down into smaller alkane and alkene molecules, smaller hydrocarbons are more useful as fuels, such as petrols. Carboncarbon double bond is the functional group of alkenes class. The process is known as catalytic cracking because it only happens in the presence of a catalyst substance which speeds up the reaction without being used up itself. The following test allows you to verify presence of unsaturated double bonds in a organic compound.
Hydrocarbons can contain carbon bound to another carbon by a double bond made up of a sigma. Hold two toothpicks side by side and attach one jellybean to each end, so that each jellybean has both toothpicks poked into it. An organic compound consisting entirely of hydrogen and carbon. How do you tell if a hydrocarbon has a double bond in its. Cracking is the name given to breaking up large hydrocarbon molecules into smaller and more useful bits. For example, decane an alkane with 10 carbons can be cracked to produce octane and ethene. Cracking fractional distillation gcse chemistry single science. When more bond energies of the bond in different molecules that are taken into consideration, the average will be more accurate. In thermal cracking, high temperatures typically in the range of 450c to 750c and pressures up to about 70 atmospheres are used to break the large hydrocarbons into smaller ones. In the unsaturated hydrocarbon, the only bond broken in the hydrocarbon is the.
Catalytic cracking uses a temperature of approximately 550c and a catalyst known as a zeolite which contains aluminium oxide and silicon oxide steam cracking uses a higher temperature of over. Find the longest chain in the molecule that contains the double bond. Addition of water alkene reacts with water, in the form of steam, to produce alcohol. An alkyne is a hydrocarbon that contains at least one carboncarbon triple bond. Reading check explain the origin of the terms saturated and unsaturated hydrocarbons. Carbon atoms linked by a double bond are bound together by two bonds, one. Gcse crude oil revise the thermal cracking reaction.
Cracking and alkenes crude oil, hydrocarbons and alkanes. In organic chemistry, an alkene is an unsaturated hydrocarbon that contains a carbon carbon double bond unsaturated hydrocarbons containing two or more double bonds and are known as alkadienes, alkatrienes, alkatetraenes, and so on, the suffix denoting the number of double bonds. We begin counting at the end of the chain closest to the double bond in this case, from the leftthe double bond spans carbons 2 and 3, so the name becomes 2 pentene. Solution the reactant is a fivecarbon chain that contains a carboncarbon double bond, so the base name will be pentene. For example, a butene molecule with a double bond between the first and second carbons is called 1butene. You should check your syllabus to find out exactly what you need to know. Products from crude oil scool, the revision website. Bondline diagrams are commonly used to represent organic molecules and simplify the structure by not showing ch bonds or carbon atoms.
Does a hydrocarbon consist of four carbon atoms with one. The reactant is a fivecarbon chain that contains a carboncarbon double bond, so the base name will be pentene. Well, 2 cannot be equal to three to start off, because a double bond it way shorter than a single bond. Gcse chemistry what is the chemistry of the cracking of. An unsaturated hydrocarbon that contains at least one carboncarbon double bond, with the general formula cnh2n. Hydrocarbons comprise the simplest series of organic compounds. A hydrocarbon with only single bonds between the carbon atoms. A unique structure can be drawn for the name of a given hydrocarbon. In this video, we look at how cracking is used to convert longchain hydrocarbons into shorterchain hydrocarbons. The existence of any double bond between carbons is the defining character. So c3h8 would have no double bonds but c2h4 would have a double bond. A unique name can be given to branched hydrocarbons using iupac nomenclature rules. Cracking oil fractions reaction conditions products. Structure and physical properties an unsaturated hydrocarbon is a hydrocarbon containing at least one double or triple bond.
A hydrocarbon that possesses one double bond belongs to the next homologous series called alkenes. What is the molarity of an hcl solution if 20 ml of acid is needed to neutralize. Ethane is the name of hydrocarbon with 2 carbon atoms and its molecular formula is c2h6. The equation below shows the cracking of a hydrocarbon compound into two different compounds. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls. A hydrocarbon with at least one double bond between the carbon a hydrocarbon with at least one triple bond between the carbon. The carbon atoms join together to form the framework of the compound, and the hydrogen atoms attach to them in many different configurations. A hydrocarbon with a triple bond between carbons is an alkyne, and the simplest compound in this class is acetylene, c 2 h 2, as shown in. Hydrocarbons are further divided into several structural types called, alkanes, alkenes, alkynes and aromatics. One possible reaction involving the hydrocarbon c15h32 might be. Cracking is used to convert long alkanes into shorter, more useful hydrocarbons. You need to understand certain chemical reactions used in a variety of.
Hydrocarbons are the principal constituents of petroleum and natural gas. However, average bonds values are not as accurate as a molecule specific bond dissociation energies. If a hydrocarbon has only single bonds, then the number of hydrogens. Bromine adds to c c double bond of alkane molecules. They contain a double bond, which is shown as two lines between two of the carbon atoms. Petrol and other fuels are produced from it using fractional distillation. Does a hydrocarbon consist of four carbon atoms with one double bond. Alkenes are hydrocarbons that contain a carboncarbon double bond. Alkenes cie igcse chemistry revision notes save my exams. An aromatic hydrocarbon or aryl hydrocarbon or occasionally arene is a hydrocarbon characterized by general changing single and double bonds among carbons. Two extremes of the thermal cracking in terms of product range are. You will learn more about these different types of hydrocarbons later in this chapter. In numbering the c atoms, we use the number 2 because it is the lower possible label.
If the double bond is in the center of the chain, the nearest substituent rule is. The words alkene and olefin are often used interchangeably. An aromatic hydrocarbon is a compound that contains a benzene ring or other similar feature. Olefins are a type of hydrocarbon containing a double bond with at least on of the substituents on both sides of the double bond being a h. As a base, you use the base name of alkanes and change the suffix ane to ene. Sometimes it will break a ch bond and lose a hydrogen atom and form a stable compound with a double bond an olefin, sometimes it will remove abstract a hydrogen from a hydrocarbon heptane in our example to generate a new alkane pentane and a new radical perhaps a radical not formed in. The combustion of 2, 2,4trimethylpentane is expressed by the following chemical equation. Sometimes it will break a ch bond and lose a hydrogen atom and form a stable compound with a double bond an olefin, sometimes it will remove abstract a hydrogen from a hydrocarbon heptane in our example to generate a new alkane pentane and a new radical perhaps a radical not formed in the initial cracking step.
An alkyne is a hydrocarbon containing triple bonds. Thermal cracking gives mixtures of products containing high proportions of hydrocarbons with double bonds alkenes. Unsaturated hydrocarbons have one or more double or triple bonds between carbon atoms. Catalysts or heat may be used to crack the alkane chain into smaller ones. These compounds are composed of carbon and hydrogen atoms in single, double, and triple bonds. The second product is an alkene, so it will follow the rule c nh 2n. Of course, the triple bond between carbons allows each carbon to bond to only one more atom. Cracking is a thermal decomposition process by which large alkane hydrocarbon molecules are broken down by passing them over a heated catalyst at high pressure. The combustion of 2,2,4trimethylpentane is expressed by the following chemical. Kekules structure, while consistent with the molecular formula and the fact that all of the hydrogen atoms of benzene are equivalent, needed to be modified to accommodate the observation that disubstitution of the ring at adjacent. The fact that all hydrocarbon combustions are exothermic is responsible for their widespread use as fuels. Cracking is an example of a thermal decomposition chemical reaction. It is possible for double or triple bonds to form between carbon atoms and even for.1242 987 373 842 1368 1527 738 663 362 1065 1553 1285 401 1475 800 430 717 1427 87 35 1260 28 1326 1121 497 1221 941 797 1047 1572 1404 727 64 723 1202 254 1471 1356 614 799 1326 1252 118 49