Methods of Cracking (GCSE Chemistry)
Methods of Cracking
What is Cracking in GCSE Chemistry?
In GCSE Chemistry, cracking refers to the process of breaking down large hydrocarbon molecules into smaller ones by heating them in the presence of a catalyst.
The process involves the use of high temperatures and pressure, along with a catalyst such as zeolite, which helps to speed up the reaction. The large hydrocarbon molecules are typically derived from crude oil, which is a complex mixture of different hydrocarbons.
Cracking is an important process in the petroleum industry, as it allows for the production of smaller, more useful hydrocarbons such as petrol, diesel, and kerosene. These smaller molecules are more volatile and have lower boiling points than the larger hydrocarbons, making them easier to use as fuels and in other applications.
Overall, understanding the process of cracking is an important part of GCSE Chemistry, as it helps students to understand how crude oil can be converted into useful products and fuels.
Cracking – GCSE Chemistry
- Hydrocarbons can be long chains. As we have just discussed, hydrocarbons are formed of hydrogen and carbon atoms. These atoms can form very long chain hydrocarbons, which are more viscous and less flammable. There are more of these types of molecules naturally present in crude oil.
- We can break down long chain hydrocarbons. Through the process of cracking, we can break down the longer chain hydrocarbons into smaller, more useful molecules. Shorter chain hydrocarbons are less viscous and more flammable.
- Cracking results in two main products. The two products are called alkanes and alkenes. Both of these products are hydrocarbons and are useful in a variety of applications.
- Alkenes are another type of hydrocarbon. Alkenes are another homologous series of hydrocarbons. They are also made of only hydrogen and carbon. Their structure is described later on.
Methods of Cracking (GCSE Chemistry)
- There are two main methods of cracking (GCSE Chemistry). Cracking can be performed in several ways, but two of the main methods include using a catalyst or using steam. These are called catalytic cracking and steam cracking.
- Both cracking methods involve heat. During cracking, the hydrocarbons are heated up in order for them to break down. This is known as thermal decomposition. High temperatures are required for both cracking methods.
- Catalytic cracking involves an aluminium oxide catalyst. The long chain hydrocarbon is turned into a gas, which then passes over a hot, powdered aluminium oxide catalyst at a temperature of about 550°C. The long chain hydrocarbon splits into shorter chain hydrocarbons (C5 to C8) as it passes over the surface of the catalyst. The hydrocarbons formed are mostly short chained alkanes. These are more useful as fuels.
- Steam cracking simply involves heat and steam. In steam cracking, the long chain hydrocarbon is turned into a gas, then mixed with steam. At very high temperatures, over 850 °C, and under pressure, the long chain hydrocarbon will split into shorter chain hydrocarbons and lots of small alkenes. The alkenes are separated from the alkanes by fractional distillation. The alkenes are used to make polymers.
Example Chemical Equations
Generally, GCSE Chemistry – Cracking equations follow this generic equation:
Worked Example: Write out the balanced equation for the cracking of C12H26, which is cracked into pentane and another hydrocarbon.
1. Write out the general equation of GCSE Chemistry – Cracking.
Long chain hydrocarbon → shorter alkane molecule + alkene
2. Fill in the formulae. We know that one of the molecules produced is pentane, so we can write in the appropriate formula.
C12H26 → C5H12 + ?
3. Calculate the number of carbons. We can look at the number of carbons on each side. On the left hand side, there are 12 carbons. On the right, there are 5 carbons, meaning that the second hydrocarbon produced must have 7 carbons.
C12H26 → C5H12 + C7H?
4. Calculate the number of hydrogens. Now we need to count the hydrogen atoms. On the left hand side we have 26 hydrogens, whilst on the right we have 12. Therefore, the second hydrocarbon produced must have 14 hydrogen atoms. Therefore, the second molecule is heptene (an alkene).
C12H26 → C5H12 + C7H14
Everyday Examples
- Hydrocarbons are essential to modern life. The products of catalytic cracking are extremely useful. Short chain hydrocarbons are essential to modern day life, because they have useful properties such as being flammable.
- Hydrocarbons can be used as fuels. Some short chain hydrocarbons can be used as fuels. For example, petrol can be used in cars. There is a high demand for fuels with small molecules.
- Hydrocarbons can form polymers. Other short chain hydrocarbons, such as alkenes, formed from thermal cracking, can go on to form polymers. For example, PVC is a polymer used in drainpipes.
FAQs
Cracking in chemistry refers to the process of breaking down large hydrocarbon molecules into smaller, more useful ones. Cracking is used in the petroleum industry to convert heavy, high-molecular weight fuels into lighter, more valuable products such as gasoline, diesel fuel, and jet fuel.
Thermal cracking: This method involves heating the hydrocarbons to high temperatures (around 500-700°C) in the absence of oxygen. The high temperature breaks the long hydrocarbon chains into smaller ones, which can then be separated and used for different purposes. Thermal cracking can be further divided into two types:
Steam cracking: In this method, steam is added to the hydrocarbons before heating, which helps to break down the molecules even further.
Coking: This method involves heating the hydrocarbons in the absence of air until they break down into solid carbon and smaller hydrocarbons.
Catalytic cracking: This method involves using a catalyst to speed up the cracking process at lower temperatures (around 450-500°C). The catalyst, typically made of zeolite or alumina, helps to break the bonds between the hydrocarbon molecules, allowing them to be broken down into smaller ones. Catalytic cracking is preferred over thermal cracking, as it produces higher yields of useful products and requires less energy.
In GCSE Chemistry, cracking is typically demonstrated in the laboratory using a simple setup. Here’s a general procedure for demonstrating cracking in GCSE Chemistry:
Materials required:
A boiling tube
A delivery tube
A Bunsen burner or a heat source
A source of hydrocarbon (e.g., paraffin wax, petroleum jelly)
Procedure:
Put a small amount of hydrocarbon in the boiling tube.
Attach the delivery tube to the boiling tube, making sure it’s well-fitted.
Heat the boiling tube using a Bunsen burner or a heat source until the hydrocarbon begins to vaporize.
Pass the vapor through the delivery tube, which should be angled downwards and placed in a beaker of cold water.
Observe the reaction, as the hydrocarbon vapor will break down into smaller molecules and form a cloudy white substance.
This setup demonstrates thermal cracking, where the hydrocarbon is broken down by heating it to high temperatures in the absence of oxygen. To demonstrate catalytic cracking, the same setup can be used, but a catalyst such as alumina or zeolite is added to the hydrocarbon before heating.
Overall, cracking is an important concept in GCSE Chemistry, and it’s important to understand the principles behind it and its various applications in the petroleum industry.
Cracking is important in chemistry because it allows for the production of smaller, more useful products from larger, less valuable ones. By breaking down large hydrocarbon molecules into smaller, more manageable components, cracking makes it possible to produce fuels and chemicals that are more useful and versatile.
There are several different methods of cracking, including thermal cracking, catalytic cracking, and hydrocracking. Thermal cracking uses heat to break down large hydrocarbon molecules, while catalytic cracking uses a catalyst to speed up the reaction. Hydrocracking uses both heat and pressure to break down large molecules into smaller ones.
Each method of cracking has its own advantages and disadvantages. Thermal cracking is simple and efficient, but it also produces a lot of waste and produces lower-quality products. Catalytic cracking is more efficient and produces higher-quality products, but it is also more complex and expensive. Hydrocracking is the most efficient and versatile method, but it also requires the most specialized equipment and conditions.
Cracking plays a crucial role in the petroleum industry, as it allows for the production of fuels and chemicals that are used in a wide range of applications, from transportation and heating to manufacturing and agriculture. Understanding cracking is essential for anyone interested in the energy and chemical industries.
Cracking is important in GCSE Chemistry because it provides students with a fundamental understanding of chemical reactions and the properties of chemicals. By studying cracking, students can learn about chemical bonding, reaction kinetics, and the properties of hydrocarbons and other chemicals. Understanding cracking is also important for students who are interested in pursuing careers in the energy or chemical industries.
Still got a question? Leave a comment
Leave a comment