Melting and Boiling Points of Alkane Compounds
Alkanes, which are non-polar organic compounds have low melting and boiling points compared with corresponding other organic compounds. By studying melting and boiling of an alkane compound, we can say whether alkane is a solid or liquid or gas at room temperature.
In this tutorial, we are going to discuss why alkane compounds have low melting and boiling points compared to alcohols or carboxylic acids by discussing theories. Then, we are going to identify what is the importance of studying melting and boiling points of alkanes. This tutorial will help you understand melting and boiling point theories too very well for other lessons too.
Content
- List of some alkanes with their melting and boiling points
- Table of melting and boiling points of some alkane compounds in Celcius
- Melting and boiling points of first ten alkanes
- How to decide whether alkane is a gas or liquid or solid according to the melting and boiling points?
- Alkanes which have low boiling point values exist as gases
- Alkanes which exist as liquids at room temperature
- Why melting and boiling points of alkanes are increased with number of carbon atoms?
- >Comparison of melting and boiling points of alkanes with other organic compounds
List of some alkanes with their melting and boiling points
Methane is a the simplest alkane and it has the lowest melting and boiling point values from alkane compounds.
Table of melting and boiling points of some alkane compounds in Celcius
| Name | Molecular Formula | Formula | Melting point (0C) | Boiling point (0C) |
|---|---|---|---|---|
| Methane | CH4 | CH4 | -183 | -162 |
| Ethane | C2H6 | CH3CH3 | -182.8 | -88.6 |
| Propane | C3H8 | CH3CH2CH3 | -187.6 | -42.1 |
| Butane | C4H10 | CH3(CH2)2CH3 | -138 | -0.5 |
| Pentane | C5H12 | CH3(CH2)3CH3 | -130 | 36 |
| Hexane | C6H14 | CH3(CH2)4CH3 | -95 | 69 |
| Decane | C10H22 | CH3(CH2)8CH3 | -95 | 69 |
| Undecane | C11H24 | CH3(CH2)9CH3 | -25.6 | 195.6 |
| Pentadecane | C15H32 | CH3(CH2)13CH3 | 9.9 | 270.6 |
| Eicosane / Icosane | C20H42 | CH3(CH2)18CH3 | 36.8 | 343 |
| Triacontane | C30H62 | CH3(CH2)28CH3 | 65.9 | 451 |
From above table, you may see melting and boiling points of alkanes are increased with number of carbon atoms. As an example, pentane (an alkane which as five carbon atoms) has a higher boiling point than butane (which has four carbon atoms).
Melting and boiling points of first ten alkanes
How to decide whether alkane is a gas or liquid or solid according to the melting and boiling points?
In this section, we are going to discuss how to decide whether alkane is a gas or liquid or solid according to the melting and boiling points.
Alkanes which have low boiling point values exist as gases
When alkanes have boiling point values less than room temperature, they exist as gases at room temperature. From above table, methane, ethane, propane and butane exist as gases at room temperature.
Alkanes which exist as liquids at room temperature
When, some alkanes have greater boiling point values than room temperature and less melting point than room temperature, those alkanes exist as liquids at room temperature. As examples, hexane, heptane and octane can be given.
Why melting and boiling points of alkanes are increased with number of carbon atoms?
With increment of molecular mass
When molecular mass is high, melting and boiling point of that compound is increased. We see, molecular mass of decane (142) is higher than methane (16). Like that, melting and boiling point of decane is higher than methane.
Amount of intermolecular forces between molecules
There are Van der Waals forces between alkane molecules. When a molecule has the chance to make more intermolecular forces with other molecules, it increases the melting and boiling point of that compound. Decane can make more intermolecular forces than methane. That is another reason why decane has a higher melting and boiling points than methane.
Comparison of melting and boiling points of alkanes with other organic compounds
- Considering organic compounds which have same number of carbon atoms, alkanes have the lowest melting and boiling points due to weak Van der Waals forces.
- Though, alkenes and alkynes do not have strong intermolecular forces, still alkanes have the lowest boiling point. As an example, ethane's melting and boiling points is lower than ethene and ethyne.
Have Questions?
LPG gas cylinders contains propane and butane as the fuels. But, both in the LPG tank Propane and Butane exist as a liquid at room temperature though their boiling points are negative. Explain the reasons.
Boiling points significantly depend on the pressure. If pressure is increased, boiling point also increases. In LPG tanks, propane and butane gases are compressed to pressurize. Then, both gases become liquid at room temperature.
