1/2 H2(g) + 1/2 I2(g) -> HI(g)
△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.
Oh so the decomposition HI is just Ea reverse? So it would be 139kJ?
yeah i have this problem for my hw and i got 139 kj/mol
We reverse the above reaction so ∆H will be -28KJ
167KJ-28KJ=139KJ
To determine the activation energy for the decomposition of HI, we need to consider the overall reaction and its activation energy.
The given reaction is:
1/2 H2(g) + 1/2 I2(g) -> HI(g)
Since the reaction is endothermic (ΔH = +28 kJ), this means that energy is required to break the bonds in the reactants and form the products.
The activation energy (Ea) for the forward reaction is given as 167 kJ. This value represents the initial energy barrier that must be overcome for the reaction to proceed. In this case, it represents the energy required for the formation of HI from H2 and I2.
For the reverse reaction (decomposition of HI), the activation energy can be calculated using the relationship:
Activation energy for reverse reaction (Ea_reverse) = Activation energy for forward reaction (Ea_forward) - ΔH
In this case, since the forward reaction has a positive ΔH (+28 kJ), the activation energy for the reverse reaction will be lower than the activation energy for the forward reaction.
Calculating the activation energy for the reverse reaction:
Ea_reverse = Ea_forward - ΔH
Ea_reverse = 167 kJ - (+28 kJ)
Ea_reverse = 195 kJ
From the calculations, we find that the activation energy for the decomposition of HI is 195 kJ.
Therefore, the correct answer is D. 195 kJ.
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