1/2 H2(g) + 1/2 I2(g) -> HI(g)

Question

△H= +28kJ

The activation energy for the formation of HI is 167kJ. The activation energy for the decomposition of HI is

A. 28kJ
B.139kJ
C.167kJ
D.195kJ

I know it is an endothermic reaction.

Answer 1

Here is a good diagram and this diagram is for an endothermic reaction and the reaction as shown is endothermic.
https://www.google.com/search?q=activation+energy+vs+reverse+activation+energy&client=firefox-a&hs=b6F&rls=org.mozilla:en-US:official&channel=sb&tbm=isch&tbo=u&source=univ&sa=X&ei=ikdAVIyiJ5PxgwTZ9IKADA&ved=0CB8QsAQ&biw=1024&bih=609#facrc=_&imgdii=_&imgrc=cktZXHQEvvng6M%253A%3BdumAy8eBEL0gHM%3Bhttp%253A%252F%252Fupload.wikimedia.org%252Fwikipedia%252Fcommons%252Fthumb%252F2%252F24%252FActivation_energy.svg%252F360px-Activation_energy.svg.png%3Bhttp%253A%252F%252Fwww.reddit.com%252Fr%252Faskscience%252Fgilded%3B360%3B288

dH + Ea reverse = Ea
28 + Ea reverse = 167

Answer 2

Oh so the decomposition HI is just Ea reverse? So it would be 139kJ?

Answer 3

yeah i have this problem for my hw and i got 139 kj/mol

Answer 4

We reverse the above reaction so ∆H will be -28KJ
167KJ-28KJ=139KJ