Potential Energy Diagrams: Understanding Exothermic and Endothermic Reactions, Study notes of Physics

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POTENTIAL ENERGY DIAGRAMS

PURPOSE

 POTENTIAL ENERGY DIAGRAMS ARE A VISUAL REPRESENTATION OF POTENTIAL

ENERGY IN A CHEMICAL REACTION

NOTE THE X AXIS IS USUALLY REACTION CORDINATE OR TIME

NOTE THE Y AXIS IS POTENTIAL ENERGY

WHERE IN THE REACTION PROGRESS/TIME

IS THE POTENTIAL ENERGY HIGHEST?

ENDOTHERMIC OR EXOTHERMIC?

Note the REACTANTS and PRODUCTS are labeled. The reactants are higher in energy (higher on y axis) then products, indicating energy is released (lost) as chemical reaction occurs, so this is an exothermic reaction. ΔH is the total energy change (enthalpy) of the reaction. ΔH is the difference in energy between the reactants and products. Is the ΔH of this reaction + or -?

 What would an endothermic reaction look like?  An endothermic reaction would show a gain in energy, meaning the products have more energy then the reactants.  Is the ΔH of this reaction + or -?

What does A represent? What does B represent? What does E represent? How would you calculate ΔH?

PRACTICE TEST QUESTIONS

What does A represent? Reactant energy What does B represent? activation energy What does E represent? product energy How would you calculate ΔH? ΔH = A – E = D D = - 890.4 kJ