Why is the C-H bond length and strength different for ethyne, ethene and ethane?

Answer: The energy associated with a chemical bond formation determines the bond strength and its proportion/degree determines its bond length.

Explanation:

When the bond energy is higher, the 'stronger' we say the bond is between the two atoms become, and the distance between its atoms (bond length) is smaller.

The length and strength of the C-H bond are different for ethine, ethylene and ethane due to the difference between the s characters (sp 3, sp 2, sp) in each chemical structure, which gives stronger bonds. For example, the length of the C-H bond in ethino is 1.06Å, which is also less than in ethane (1.09Å) or ethylene (1.08Å).