Which gas, acetylene (#C_2H_2#), a gas used in welding, or ethane (#C_2H_6#) has a stronger carbon to carbon bond energy and bond length? Explain why.

1 Answer
anor277
Mar 31, 2017

The triply bonded acetylene molecule............

Explanation:

The modern chemical bond is conceived to be a region of high electron density between 2 positively charged atomic nuclei, such that internuclear is repulsion is negated, and a net attractive force results. The idea can be extended to multiple bonding, where electron density is concentrated in planes NORMAL to the #"atom-atom vector"#, but which still allows nuclear/electronic interaction.

So let's look at the bond dissociation energies. As chemists, as physical scientists, we must examine the data:

Try this site............

And representative values for #C-C# bond lengths for #H_3C-CH_3#, #H_2C=CH_2#, and #H_3C-=CH_3# are #1.54xx10^-10*m#, #1.34xx10^-10*m#, and #1.21xx10^-10*m#.

And #C-C# bond energies:

#C-C:#, #84*kcal*mol^-1#;

#C=C#, #150*kcal*mol^-1#;

#C-=C#, #200*kcal*mol^-1#;

Are these data consistent with the argument just proposed?

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