Draw an energy diagram for an exothermic reaction that yields 75 kcal/mol. The activation energy is 30KCal/mole
[Energy Diagram Description]
markdownCopyEditEnergy (kcal/mol)
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70| ‡
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40| / \
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| Reactants / \ Products
-35|-------------------/ \-------------------
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Reaction Progress
Explanation
In chemical thermodynamics, an energy diagram is a graphical representation that shows the energy changes during the course of a chemical reaction. It helps visualize the energy of the reactants, the transition state, and the energy of the products. For an exothermic reaction, energy is released to the surroundings, and the energy of the products is lower than that of the reactants.
In this example, the reaction has a ΔH (enthalpy change) of −75 kcal/mol, meaning the products are 75 kcal/mol lower in energy compared to the reactants. The activation energy (Ea) is 30 kcal/mol, which is the energy barrier that must be overcome for the reactants to reach the transition state.
The diagram begins with the reactants on the left at a certain energy level (say, 0 kcal/mol for reference). The energy then increases as the reaction progresses, peaking at the transition state, which represents the highest energy point and is 30 kcal/mol above the reactants. This peak indicates the unstable, high-energy intermediate configuration through which the molecules must pass.
After reaching the transition state, the energy drops sharply, ending at the products, which are at −75 kcal/mol relative to the reactants. This drop confirms that the reaction is exothermic. The large energy release implies a stable product, and the relatively low activation energy suggests that the reaction could proceed readily under appropriate conditions.
This energy profile is crucial in predicting reaction spontaneity and rate. While ΔH indicates thermodynamic favorability, the activation energy influences the reaction rate—even exothermic reactions may proceed slowly if Ea is too high. Catalysts lower Ea, speeding up the reaction without altering ΔH.
