# Potential Energy Diagrams Made Easy Exothermic followed by Endothermic.

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Potential Energy Diagrams Made Easy Exothermic followed by Endothermic

In any exothermic reaction, energy would be a product Potential energy in kJ/mol time

In any exothermic reaction, energy would be a product The potential energy of the reactants, labeled R, is steady, because it is based upon the actual chemicals. That line is flat to start. Potential energy in kJ/mol time R

In any exothermic reaction, energy would be a product As you add energy, the energy of the reactants increases Potential energy in kJ/mol time R

In any exothermic reaction, energy would be a product As you add energy, the energy of the reactants increases Until you reach the top of the arch, the minimum amount of energy needed to make this reaction go forward, the ACTIVATION ENERGY. Potential energy in kJ/mol time R

In any exothermic reaction, energy would be a product As you add energy, the energy of the reactants increases The reaction “pays back the activation energy first. Potential energy in kJ/mol time R The green arrow represents the activation energy required for this reaction to start.

In any exothermic reaction, energy would be a product The reaction continues to give off more energy (that’s what exothermic reactions do). The reaction moves to completion. Potential energy in kJ/mol time R

In any exothermic reaction, energy would be a product The reaction finishes, the products end with less potential energy than the reactants started with (labeled P). This Potential energy remains a constant as well. Potential energy in kJ/mol time R P

In any exothermic reaction, energy would be a product The net change in potential energy between the starting & the ending potential energy is called the ∆H. In this case, since the difference is LOWER, the ∆H is negative. A ―∆H is exothermic. Potential energy in kJ/mol time R P ― ∆H

The activated complex is a very short lived melding of the reactants as the become products. For about one ten trillionth of a second they are not reactants or products, but an intermediate substance. The bonds are breaking and reforming as the products form. This is labeled with the star. Potential energy in kJ/mol time R This is the “point of no return” for the reaction. P ― ∆H

In any exothermic reaction, energy would be a product ∆H is the NET difference between starting and ending energies. The activation energy is required to start the reaction, but it is “paid back”. Only the NET difference is the energy released to the environment. When a reaction releases energy, that’s exothermic. Potential energy in kJ/mol time R P ― ∆H

In any exothermic reaction, energy would be a product If a catalyst is used to speed up a chemical reaction, the potential energy of the reactants and products does not change. The ∆H doesn’t either. What does happen is that the ACTIVATION ENERGY is lowered, making the reaction easier to go forward. Potential energy in kJ/mol time R P ― ∆H

In any exothermic reaction, energy would be a product Catalysts lower activation energy by providing an easier, alternative pathway for the reaction to proceed. This makes the reaction faster, but not Potential energy in kJ/mol time R P ― ∆H Blue arrow is the lower activation energy required due to the catalyst. The catalyst can only changes the activation energy, it cannot change potential energies, and therefore, cannot change the ∆H either.

Endothermic Potential Energy Diagrams ΔH is positive Energy is absorbed to make the reaction go forward.

In any endothermic reaction, energy would be a reactant. The reactant Potential Energy is a constant because of what the reactants are. It’s labeled “R”. Potential energy in kJ/mol time R

In any endothermic reaction, energy would be a reactant. As you add energy, the energy levels rise, towards the minimum needed to cause a reaction, the ACTIVATION ENERGY. Potential energy in kJ/mol time R

In any endothermic reaction, energy would be a reactant. If you reach the top of the arch, if you provide enough energy, the reaction goes forward and “pays back” some energy of activation. Potential energy in kJ/mol time R

In any endothermic reaction, energy would be a reactant. In an endothermic reaction, the products “P”, have more energy than the reactants they started with. Potential energy in kJ/mol time R P

In any endothermic reaction, energy would be a reactant. The ACTIVATION ENERGY is from the starting potential energy to the top of the curve, the minimum energy needed to make this reaction start. Potential energy in kJ/mol time R P A.E.

In any endothermic reaction, energy would be a reactant. The difference between the potential energy at the start of the reaction, and the end of the reaction, between reactants and products, is the ΔH. Potential energy in kJ/mol time R P ∆HA.E.

In any endothermic reaction, energy would be a reactant. A catalyst for this reaction would require less activation energy, providing an easier, alternate path for the reaction. It does not change potential energies for reactants or products, or the ΔH. Potential energy in kJ/mol time R P Lower A.E.

In any endothermic reaction, energy would be a reactant. The star represents that moment in time where the reactants are reacting, no longer exactly what they were, but not quite fully formed into the products. The ACTIVATED COMPLEX is that in between state. Potential energy in kJ/mol time

Potential energy diagrams show the energy flow of a chemical reaction, from the starting point with the reactants, through the energy “spark” that will start a reaction, through the formation of the products at the end. A chemical reaction will result in a net gain of energy (endothermic, +∆H) or a net loss of energy (exothermic, ─ ∆H). The energy absorbed comes from the immediate environment of the reaction, which makes that feel colder, since it’s a loss of kinetic energy. In an exothermic reaction, since the products have less energy than they started, the energy is not “lost”, rather it is let go into the environment, making that feel hot. Without enough energy, the activation energy, you will not get the reaction to move forward to completion. You might get warmer reactants, but not products.

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