Melting point

Chemistry Level 3

Arrange the following alkanes in decreasing order of their $\color{#3D99F6}{\text{melting point}}$ .

$\large \text{A) Ethane} \quad \quad \text{B) Propane} \quad \quad \text{C) Butane}$

Bonus : Molecular formula of given alkanes :

Ethane $\ \ : C_2 H_6$
Propane $\ : C_3 H_8$
Butane $\ \ : C_4 H_{10}$

Try more chemistry problems here

B > A > C B > C > A A > B > C C > A > B C > B > A A > C > B

1 solution

Tanishq Varshney
Oct 27, 2015

This is because $\text{even-numbered alkanes pack closer together more easily, making it}$ $\text{more difficult to break down the solid material.}$ and more the molecular weight , more are the vander waal forces of attraction and more is the melting point.

Keeping these two points in our mind we get the answer.

Bonus question: Why boiling point of Propane is greater than Ethane ?

Akhil Bansal - 5 years, 7 months ago

Do u mean to say isobutane??

Tanishq Varshney - 5 years, 7 months ago

Sorry, i mean to say ethane, not butane...
Melting point of Ethane is more than Propane but Boiling point of Propane is higher than Ethane. How?

Akhil Bansal - 5 years, 7 months ago

@Akhil Bansal – https://upload.wikimedia.org/wikipedia/commons/8/82/AlkaneBoilingMeltingPoint.png

"The melting points of the alkanes follow a similar trend to boiling points for the same reason as outlined above. That is, (all other things being equal) the larger the molecule the higher the melting point. There is one significant difference between boiling points and melting points. Solids have more rigid and fixed structure than liquids. This rigid structure requires energy to break down. Thus the better put together solid structures will require more energy to break apart. For alkanes, this can be seen from the graph above (i.e., the blue line). The odd-numbered alkanes have a lower trend in melting points than even numbered alkanes.

This is because even numbered alkanes pack well in the solid phase, forming a well-organized structure, which requires more energy to break apart. The odd-number alkanes pack less well and so the "looser" organized solid packing structure requires less energy to break apart."

[by https://en.wikipedia.org/wiki/Alkane] An only exception!

Lu Chee Ket - 5 years, 4 months ago

Melting point

Try more chemistry problems here

1 solution

0 pending reports