On an energy profile diagram for an exothermic reaction
Correct answer: A. the products lie at a lower energy level than the reactants
- A. the products lie at a lower energy level than the reactants
- B. the products lie above the reactants
- C. there is no activation energy barrier
- D. the activation energy is always zero
Explanation
An exothermic reaction releases energy to the surroundings, so the products sit lower and the enthalpy change is negative, but the curve still rises to a peak first because the activation barrier must be crossed. Confusing the barrier height with the overall enthalpy change is the classic error when reading these diagrams. An endothermic profile has the products higher than the reactants.
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About Activation Energy and Activated Complex
Activation energy is the minimum energy reactant particles need to form the activated complex, or transition state, during a reaction. Energy profile diagrams show the forward and reverse activation energies, while catalysts provide an alternative pathway with lower activation energy without changing the reaction enthalpy.
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