The reaction C4H10 ---> C2H6 + C2H4 has activation energy (Ea) of 450 kJ/mol, and the Ea of the reverse reaction is 250 kJ/mol. Estimate ΔH, in kJ/mol, for the reaction as written above.

ΔH = 200 kJ/mol

Explanation:

Step 1: Data given

activation energy (Ea) is:  450 kJ/mol

activation energy (Ea) of the reverse reaction is 250 kJ/mol

Step 2: The balanced equations

C4H10 ---> C2H6 + C2H4  Ea = 450 kJ/mol

C2H6 + C2H4 ---> C4H10    Ea = 250 kJ/mol

Step 3: Calculate ΔH

Since the reverse reaction has a lower activation energy, this means we need less reaction for the reverse reaction to happen. We can say the reaction absorbs energy, so this is the endothermic reaction.

Ea ( of the forward reaction) = ΔH + Ea (of the reverse reaction)

ΔH = Ea ( of the forward reaction) - Ea (of the reverse reaction)

ΔH = 450 kJ/mol - 250 kJ/mol

ΔH = 200 kJ/mol

Since the reactionis endothermi, ΔH is positive

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.