[lrarava]

the underscore part is activation energy, but I don't understand why the graph x-axis is kinetic energy...can anyone explain it? I'd really appreciate it.

[dagr8est]

Your image isn't showing up.

[lrarava]

thanks for reminding
i had reattached the picture

[Hunt]

Well remember that molecules or atoms in random motion have translational and rotational Kinetic energy. Kinetic energy is simply the energy of motion, as the velocity increases, K.E. increases. For a rxn to occur, the reactants must have a minimal energy greater or equal to the activation energy( along with other factors ).

When a catalyst is added to a certain rxn, it provides a different path with a lower activation energy leading to the formation of the same products. Hence, the K.E. needed for this rxn to take place will be lower than that previously needed in the absense of the catalyst. Notice in graph (a) [ no catalyst ] E_a was greater ( farther to the right ) than E_a in graph (b) [ catalyst ]

I hope this helps you a bit ...

[lrarava]

Thank you, but can it relate to thermal energy??
since activation energy can obtained from both thermal energy and kinetic energy tp break bonds of reactans, so the reaction can occur.

[Hunt]

Thermal energy is understood to be nothing more than the mechanical energy of the atoms and/or molecules of a certain system. In precise, Thermal energy is the vibrational energy of the disordered motion of molecules. Therefore, when translational Kinetic energy is included, it's part of the M.E. of the system , so why use different names?

since activation energy can obtained from both thermal energy and kinetic energy tp break bonds of reactans, so the reaction can occur

I'm not sure what you mean. According to the collision model, the energy required to break the bonds of reacting molecules comes from their kinetic energies before collision. As they are broken, the K.E. is converted into potential energy stored in the new bonds formed.

Activation energy is just the threshold enery - the minimum energy to be overcome for a rxn to take place. It is independent of thermal energy. You can see this by plotting Lnk ( rate const ) versus 1/T , the decreasing slope is -E_a / R . Notice that  E_a is const irrespetive of the Temp.