CNG vs LPG: Chemical Composition, Properties, and Uses Compared
Difference Between CNG and LPG is essential in chemistry and helps students understand various practical and theoretical applications related to gas fuels, energy, and environmental science. This topic is especially important in understanding alternative fuels and their applications in daily life and industry.
What is Difference Between CNG and LPG in Chemistry?
Difference Between CNG and LPG refers to the comparison between Compressed Natural Gas and Liquefied Petroleum Gas. CNG (mainly methane) and LPG (propane and butane mixture) are both gaseous fuels but differ in chemical composition, storage, uses, and environmental impact. This concept appears in chapters related to fuel types, alternative energy, and combustion in chemistry, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
The molecular formula for the main component of CNG is CH4 (methane), while LPG contains mainly C3H8 (propane) and C4H10 (butane). CNG is a natural gas, and LPG is a petroleum-derived fuel. Both are hydrocarbons, but their source and chemical components differ.
Preparation and Synthesis Methods
CNG is obtained by compressing natural gas, which is sourced from natural gas wells and coal bed methane. It is compressed to 200–250 bar. LPG is produced during crude oil refining or extracted from natural gas streams. It is liquefied under moderate pressure for storage and transport. Both require special cylinders for safe storage.
Physical Properties of Difference Between CNG and LPG
| Property | CNG | LPG |
|---|---|---|
| Main Constituent | Methane (CH4) | Propane (C3H8), Butane (C4H10) |
| Physical State in Cylinder | Compressed Gas | Liquefied Gas |
| Storage Pressure | High (200-250 bar) | Low (about 7.5-15 bar) |
| Ignition Temperature | 540°C | Around 410°C |
| Energy Content (Calorific Value) | ~50 MJ/kg | ~46 MJ/kg |
| Density (air=1) | 0.7 (lighter than air) | 1.5-2 (heavier than air) |
| Colour & Smell | Colourless, Odourless (odorant added) | Colourless, Odourless (odorant added) |
Chemical Properties and Reactions
Both CNG and LPG are hydrocarbons and undergo combustion reactions to produce carbon dioxide and water vapor, releasing energy. However, CNG has a higher octane number and burns more cleanly, with fewer unburned residues and lower emissions of CO and particulates compared to LPG.
Frequent Related Errors
- Confusing Difference Between CNG and LPG with other fuel types like LNG or biogas.
- Thinking both have the same storage conditions (overlooking that LPG is stored as liquid and CNG is stored as compressed gas).
- Ignoring the difference in safety risks due to their density (CNG rises if leaked, LPG settles and poses fire risk).
Uses of Difference Between CNG and LPG in Real Life
CNG is mostly used as a fuel for vehicles (buses, cars, auto-rickshaws) and in industries that require clean combustion. LPG is commonly used in domestic cooking, heating, and small industries. Both are considered cleaner alternatives to petrol, diesel, and wood. The difference influences their choice in different applications.
Relevance in Competitive Exams
Difference Between CNG and LPG is frequently asked in JEE Main, NEET, and school exams. Questions appear as direct “difference between” tables, MCQs on uses, chemical properties, and environmental impact. Understanding this helps students tackle applied chemistry and environmental science sections confidently.
Relation with Other Chemistry Concepts
Difference Between CNG and LPG is closely related to topics such as Fuel Types and Effects of Burning Fossil Fuels, helping students build a conceptual link between physical properties, energy content, and environmental protection. You can also explore Combustion and Flames for more details on fuel behavior.
Step-by-Step Reaction Example
1. Combustion of CNG (Methane) in air:CH4 + 2O2 → CO2 + 2H2O
2. Explain:
Methane reacts with oxygen to produce carbon dioxide and water, releasing energy as heat.
3. Combustion of LPG (Propane):
C3H8 + 5O2 → 3CO2 + 4H2O
4. Reaction conditions:
Both reactions require an ignition source and sufficient air (oxygen). CNG requires higher ignition temperature than LPG.
Lab or Experimental Tips
Remember Difference Between CNG and LPG by the visual cue that CNG cylinders are larger and heavier (for high pressure), while LPG cylinders are smaller for easy storage of liquid fuel. Vedantu educators often point out this difference in live sessions to help students recall which gas is which during practicals and theory exams.
Try This Yourself
- List three key differences between CNG and LPG.
- Explain why LPG is more suitable for domestic cooking.
- Write the balanced chemical equation for combustion of butane (main LPG component).
- Identify which gas disperses faster in case of a leakage and explain why.
Final Wrap-Up
We explored the Difference Between CNG and LPG—their composition, physical and chemical properties, uses, and environmental impact. Understanding CNG vs LPG is vital for both academic and real-life applications, especially for clean fuel awareness. For more in-depth explanations and exam-prep tips, explore live sessions, notes, and concept videos on Vedantu.
FAQs on Difference Between CNG and LPG — Chemistry Explained
1. What is the main difference between CNG and LPG?
CNG (Compressed Natural Gas) is primarily methane, stored as a compressed gas. LPG (Liquefied Petroleum Gas) is a mixture of propane and butane, stored as a liquid under pressure. This difference in storage stems from their differing boiling points and ease of liquefaction.
2. Which is safer, CNG or LPG?
CNG is generally considered safer because it's lighter than air and disperses quickly in case of a leak. LPG, being heavier than air, can accumulate in low-lying areas, posing a greater risk of explosion.
3. Can LPG be used in a CNG car?
No. CNG and LPG vehicles require different engine modifications and fuel systems. They are not interchangeable.
4. Which is better for home cooking: CNG or LPG?
LPG is more commonly used for home cooking due to its higher calorific value and easier storage in domestic cylinders. However, CNG is becoming increasingly popular in some regions for its cleaner burning properties.
5. What are the environmental benefits of using CNG?
CNG produces significantly fewer greenhouse gases and other pollutants compared to LPG and traditional fuels like petrol and diesel. This contributes to cleaner air and a reduced carbon footprint.
6. What is the chemical composition of CNG and LPG?
CNG is mainly composed of methane (CH₄). LPG is a mixture of propane (C₃H₈) and butane (C₄H₁₀), with propane typically being the major component.
7. How does the calorific value affect the choice of fuel?
Calorific value, the amount of heat released per unit mass, is a crucial factor. LPG has a higher calorific value than CNG, meaning it releases more energy per unit mass. This makes LPG suitable for applications needing high energy density, such as cooking. However, CNG's lower calorific value is often offset by its lower cost and cleaner burning.
8. What are the advantages and disadvantages of CNG and LPG for vehicles?
CNG Advantages: Cleaner burning, lower cost per unit energy. CNG Disadvantages: Lower calorific value, requiring larger tanks, less energy per tank fill. LPG Advantages: Higher calorific value, greater range per tank fill. LPG Disadvantages: Higher cost, heavier than air, increased risk in case of leaks.
9. What safety precautions should be taken when using CNG and LPG?
Regular cylinder inspections, proper ventilation, and immediate attention to any leaks are crucial for both fuels. Never use these fuels near open flames or sparks.
10. How do CNG and LPG compare in terms of their impact on engine life?
Both CNG and LPG are relatively clean-burning fuels and generally have minimal negative impacts on engine life. However, regular vehicle maintenance is essential for optimum performance and longevity regardless of the fuel type.
11. What are the sources of CNG and LPG?
CNG is sourced from natural gas wells and coal bed methane. LPG is obtained as a byproduct of crude oil refining and natural gas processing.
12. What is the difference in the physical state of CNG and LPG at normal temperature and pressure?
At normal temperature and pressure, both CNG and LPG are gases. However, LPG is easily liquefied under moderate pressure, allowing for compact storage in cylinders, while CNG requires much higher pressure to remain in a gaseous state.
