What is combustion of hydrocarbons balanced chemical equations types and examples
Combustion is the process of burning some substances at high temperatures. It is an exothermic reaction that happens between fuel and oxygen, producing a gaseous substance (smoke) as a product. Combustion is of two types, one is complete combustion and another is incomplete combustion. Hydrocarbons are compounds made only with the elements of hydrogen and carbon. Hydrocarbons are broadly classified as alkanes, alkenes, and alkynes.
Complete Combustion of Alkanes
It is the process of burning the alkane in the presence of sufficient air or oxygen; it produces carbon dioxide, water, and a huge amount of heat as a product. For example:
With Propane ( C3H8 ), the complete reaction is given as follows:
C3H8 + O2 → 3CO2 + 4H2
With Butane (C4H10), the complete combustion reaction is given as follows:
C4H10 + O2 → 4CO2 + 5H2
The generalised form of this reaction is as follows:
CnH2n+2 + ((3n + 1)/2) O2 → nCO2 + (n+1)H2O
In general, it is used as a fuel since it produces a huge amount of heat.
Incomplete Combustion of Alkanes
It is the process of burning alkane in the absence of sufficient air or oxygen. It produces carbon and carbon monoxide as a product whereas carbon monoxide is a by-product that is a colorless poisonous gas. For example:
With methane (CH4), the incomplete reaction is given as follows:
CH4 + O2 → C + 2H2O
The carbon black which is formed as a product of the combustion process is used in the manufacturing of inks.
Combustion of Hydrocarbons (Alkene)
Complete Combustion of Alkene
Like the same as an alkane, alkene also undergoes complete combustion. It occurs in the presence of excess air or oxygen for combustion. For example:
C2H4 + 3O2 → 2CO2 + 2H2O
Incomplete Combustion of Alkene
It happens in the absence of oxygen during the combustion process and carbon monoxide is formed as a product instead of carbon dioxide. For example:
C2H4 + 2O2 → 2CO + 2H2O
Combustion of Hydrocarbons
It is the process of burning the hydrocarbons which leads to breaking the bonds either in the presence or in the absence of excess oxygen.
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Complete Combustion of Hydrocarbons
It is the process of burning hydrocarbons in excess of oxygen and yields carbon dioxide and water as a product. Oxygen should be present in excess and hydrocarbon is used as a limiting reagent to achieve this process.
Incomplete Combustion of Hydrocarbons
It is a process of burning hydrocarbons in the absence of excess oxygen and produces the most oxidized form of carbon which is carbon dioxide as a product. We should have oxygen as a limiting reagent and hydrocarbons as an excess reagent.
The “sooty” flame is produced by the incomplete combustion of a hydrocarbon, due to the presence of carbon ( C ).
Hydrocarbon Formula of Complete Combustion
The general form of this combustion reaction is as follows:
Methane + oxygen gas → carbon dioxide gas + water vapour
Hydrocarbon Formula of Incomplete Combustion
The general form of this incomplete reaction is given as follows:
methane + oxygen gas → solid carbon + water vapour
Types of Combustion
Different types of combustion are as follows:
Rapid combustion: Rapid combustion is a type of combustion when quick heat energy is needed for the reaction to take place. A large amount of heat and light energy is produced in this type of reaction. The combustion occurs as long as the fuel is available. For example, when we light a candle, it will burn until the wax burns out.
Spontaneous combustion: This type of combustion occurs spontaneously. This means that this type of reaction does not need any external energy for the combustion to begin. It occurs due to self-heating. This type of combustion takes place in substances with low-ignition temperatures. The process starts as soon as the temperature rises above the ignition point. The combustion will take place in the presence of oxygen.
Explosive combustion: This is a type of combustion in which the reaction occurs very rapidly. This combustion occurs when something is ignited to produce heat, light, and sound energy as in firecrackers.
Solved Examples
Ethanol is a fuel source in an alcohol lamp. The formula for ethanol is given by C2H5OH. Write the balanced equation for the process of combustion of ethanol.
Solution:
Step 1: Think of the given problem. The question is given on ethanol which is a reactant and also with oxygen. Carbon dioxide and water are the products.
Step 2: Write the skeleton equation and solve:
C2H5OH (l) + O2 (g) → CO2 (g) + H2O (g)
Now balance the equation.
C2H5OH (l) + 3O2 (g) → 2CO2 (g) + 3H2O (g)
Evaluate the number of each element present on the reactant and product side.
Interesting Facts:
Nearly 21% of the air in the atmosphere is filled with oxygen. To get complete combustion, it is necessary to have plenty of air, mainly oxygen in it. Natural gas and petrol are such fuels that have hydrocarbons.
A hydrocarbon is a compound made of only 2 elements namely carbon and hydrogen atoms.
The interesting thing is, that it is found in crude oil and can be separated by fractional distillation. The bond between them is non-polar covalent bonds.
Summary
Combustion includes the burning of organic substances and it is a chemical reaction.
Combustion includes burning of the organic compound and releasing carbon dioxide and water and releasing a lot of heat energy.
Combustion is an important process and hydrocarbons are the main source of energy for domestic and industrial processes.
Combustion of fossil fuels such as natural gas is an example of such a chemical reaction.
FAQs on Combustion of Hydrocarbons Complete Reaction Guide
1. What is combustion of hydrocarbons?
Combustion of hydrocarbons is an exothermic chemical reaction in which a hydrocarbon reacts with oxygen to produce carbon dioxide (CO2) and water (H2O), releasing heat and light.
- Hydrocarbons contain only carbon and hydrogen.
- General word equation: Hydrocarbon + O2 → CO2 + H2O + energy.
- Example: CH4(g) + 2O2(g) → CO2(g) + 2H2O(l).
- This reaction is the basis of fuels used in engines, heating, and power generation.
2. What is the general equation for complete combustion of a hydrocarbon?
The general equation for the complete combustion of a hydrocarbon CxHy is CxHy + (x + y/4)O2 → xCO2 + (y/2)H2O.
- All carbon atoms form CO2.
- All hydrogen atoms form H2O.
- Sufficient oxygen is required for complete combustion.
- This formula helps balance combustion equations quickly in stoichiometry problems.
3. What is the difference between complete and incomplete combustion of hydrocarbons?
Complete combustion produces CO2 and H2O, while incomplete combustion produces CO and/or solid carbon (soot) due to limited oxygen.
- Complete combustion (excess O2): clean blue flame.
- Incomplete combustion (limited O2): yellow smoky flame.
- Example of incomplete combustion: 2CH4(g) + 3O2(g) → 2CO(g) + 4H2O(l).
- Carbon monoxide (CO) is toxic and forms when oxygen supply is insufficient.
4. How do you balance a combustion reaction of a hydrocarbon?
To balance a combustion reaction, balance carbon first, then hydrogen, and finally oxygen.
- Step 1: Balance C atoms by adjusting CO2.
- Step 2: Balance H atoms by adjusting H2O.
- Step 3: Balance O atoms by adjusting O2.
- Example (ethane): 2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(l).
5. Why is combustion of hydrocarbons an exothermic reaction?
Combustion of hydrocarbons is exothermic because more energy is released when forming CO2 and H2O bonds than is required to break the C–H and O=O bonds.
- Strong C=O and O–H bonds are formed in the products.
- Energy difference appears as heat and light.
- This released energy is used in fuels for engines and heating systems.
6. Can you give an example of combustion of an alkane?
An example of combustion of an alkane is the burning of propane: C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l).
- Propane (C3H8) is a saturated hydrocarbon.
- This reaction is used in LPG gas cylinders.
- It releases significant heat, making it suitable as a fuel.
7. What are the products of incomplete combustion of hydrocarbons?
The products of incomplete combustion are carbon monoxide (CO), carbon (C, soot), water (H2O), and sometimes small amounts of CO2.
- Occurs when oxygen supply is limited.
- Example: CH4(g) + O2(g) → C(s) + 2H2O(l) (oxygen-deficient conditions).
- CO is poisonous because it binds strongly to hemoglobin in blood.
8. How do you calculate the amount of oxygen needed for complete combustion?
To calculate oxygen required for complete combustion, use the balanced chemical equation and apply mole ratios from stoichiometry.
- Write and balance the equation.
- Use coefficients to find the mole ratio between hydrocarbon and O2.
- Convert moles to mass or volume if needed.
- Example: From CH4 + 2O2 → CO2 + 2H2O, 1 mole of CH4 requires 2 moles of O2.
9. Why does incomplete combustion produce a yellow flame?
Incomplete combustion produces a yellow flame because hot carbon particles (soot) glow and emit yellow light.
- Occurs when oxygen is insufficient.
- Unburnt carbon particles become incandescent.
- Common in a Bunsen burner with the air hole closed.
10. What is the environmental impact of hydrocarbon combustion?
Hydrocarbon combustion contributes to carbon dioxide emissions, air pollution, and climate change.
- CO2 is a greenhouse gas causing global warming.
- Incomplete combustion produces CO and soot, contributing to air pollution.
- High-temperature combustion in engines can also form nitrogen oxides (NOx).
- Cleaner fuels and complete combustion reduce environmental impact.
