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Reaction profiles for exothermic and endothermic reactions

Energy changes • Exothermic and endothermic reactions

Key concepts

What you'll likely be quizzed about

  • A reaction profile plots energy on the vertical axis against reaction progress on the horizontal axis.
  • The starting point represents the energy of the reactants, while the finish point shows the energy of the products.
  • A curve connects these two points, rising to a peak that signifies the highest-energy arrangement in the reaction pathway.

Flashcards

Test your knowledge with interactive flashcards

What is the correct sign for ΔH in an endothermic reaction?

Click to reveal answer

Positive.

Key notes

Important points to keep in mind

Label reactants, products, peak, Ea, and ΔH on each diagram.

Determine exothermic or endothermic by comparing energy levels of products and reactants.

A negative ΔH indicates an exothermic reaction, while a positive ΔH indicates an endothermic reaction.

Ea represents the energy difference from reactants to the peak, not from products to the peak.

Catalysts lower Ea but do not alter ΔH.

Diagrams are qualitative unless numerical energy values are provided on the axis.

Multiple peaks indicate a multi-step reaction mechanism with intermediates.

Energy axis scale may vary between diagrams; compare positions, not absolute heights.

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