# Activation energy-can someone help been stuck for a while

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#1
activation energy is the minimum energy required to break some reactant bonds and start the chemical reaction.

I know on an energy diagram for an exothermic reaction this means the difference between the reactants and the peak.

the reactants is at eg 1000j(I know it can't be measured but for this sake) and peak is 1600j

let's say it was 600j (the difference)

the activation energy would then be 600j

but in a Boltzmann distribution curve the shaded area to the right in my book it states more molecules have an energy greater or equal to the activation energy

this means that the molecules have an energy equal to or more then 600j. if a molecule has 600j this isn't enough surley as molecules require 1600j to reach the peak. but using the logic from the diagram the activation energy is only at 600j

I think I've misunderstood something along the way. can you help clear the gap in my knowledge from above.

thanks
Last edited by WWEKANE; 1 year ago
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1 year ago
#2
(Original post by WWEKANE)
activation energy is the minimum energy required to break some reactant bonds and start the chemical reaction.

I know on an energy diagram for an exothermic reaction this means the difference between the reactants and the peak.

the reactants is at eg 1000j(I know it can't be measured but for this sake) and peak is 1600j

let's say it was 600j (the difference)

the activation energy would then be 600j

but in a Boltzmann distribution curve the shaded area to the right in my book it states more molecules have an energy greater or equal to the activation energy

this means that the molecules have an energy equal to or more then 600j. if a molecule has 600j this isn't enough surley as molecules require 1600j to reach the peak. but using the logic from the diagram the activation energy is only at 600j

I think I've misunderstood something along the way. can you help clear the gap in my knowledge from above.

thanks
The level shown in an energy diagram is the internal chemical potential energy. The activation energy is the "extra" kinetic energy that must be applied to break the bonds.

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#3
so on the Boltzmann distribution curve is it the top of the curve.

if so why is it activation energy as let's says molecule has 1000 j of energy it only needs 600j so it's activation energy will be 600j not the 1600j?

Last edited by WWEKANE; 1 year ago
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1 year ago
#4
(Original post by WWEKANE)
so on the Boltzmann distribution curve is it the top of the curve.

if so why is it activation energy as let's says molecule has 1000 j of energy it only needs 600j so it's activation energy will be 600j not the 1600j?

Maxwell Boltzmann shows only the distribution of kinetic energies over all the particles.

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#5
ok I think I'm starting to get it. so in an enthalpy diagram it looks at the enthalpy of the reactants and sees how much energy it needs extra to get to the energy needed for it to react . but in Maxwell Boltzmann it just looks at how much energy it needs to react without taking into account it's initial energy just what it needs to get to(ie the peak of the curve in an energy profile diagram)?
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1 year ago
#6
(Original post by WWEKANE)
ok I think I'm starting to get it. so in an enthalpy diagram it looks at the enthalpy of the reactants and sees how much energy it needs extra to get to the energy needed for it to react . but in Maxwell Boltzmann it just looks at how much energy it needs to react without taking into account it's initial energy just what it needs to get to(ie the peak of the curve in an energy profile diagram)?
You have not read my posts very carefully.

The energy level diagram (reaction profile) shows only the chemical internal energy. The reacting particles gain more of this through a collision until eventually the bonds break. They get the "extra" from the kinetic energy of the colliding particles.

The MB curve shows the distribution of kinetic energy over particles at a given temperature.
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#7
what's the difference between chemical internal energy and kinetic energy ?
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1 year ago
#8
(Original post by WWEKANE)
what's the difference between chemical internal energy and kinetic energy ?
Chemical internal energy is a form of POTENTIAL energy. It is a function of the nature of the substance related to every other substance in the universe.
Kinetic energy is the actual motion of the particles. Directional kinetic energy is given by 1/2mv2
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#9
I think its starting to make sense. so particles have an internal energy. they must collide with a certain amount of energy so they can convert kinetic energy into heat energy which will lead to the eventual breaking of the chemical bond.

So molecules must collide with this energy so enough can be converted into chemical potential energy to break the bond?

IF YOU DON'T MIND ME ASKING DO BOTH REACTANT PARTICLES NEED TO COLLIDE WITH THIS ENERGY OR ONLY ONE? thanks
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1 year ago
#10
(Original post by WWEKANE)
I think its starting to make sense. so particles have an internal energy. they must collide with a certain amount of energy so they can convert kinetic energy into heat energy which will lead to the eventual breaking of the chemical bond.

So molecules must collide with this energy so enough can be converted into chemical potential energy to break the bond?

IF YOU DON'T MIND ME ASKING DO BOTH REACTANT PARTICLES NEED TO COLLIDE WITH THIS ENERGY OR ONLY ONE? thanks
When they collide they convert kinetic energy into chemical potental energy, that's why there is a hump in the reaction profile (which you will remember shows the chemical potential energy).

The collision may be between two reacting particles or simply between one and the walls of the container, or another irrelevant particle.

As long as there is enough kinetic energy to provide the required chemical potential energy of activation, then the reaction can proceed.
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