Exothermic reactions
3 marks · NormalDescribe how the energy profile diagram of an exothermic reaction differs from that of an endothermic reaction. Your answer should refer to the relative positions of reactants and products and the direction of energy change.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
In an exothermic reaction, the energy profile diagram shows the products at a lower energy level than the reactants, with energy released to the surroundings (ΔH is negative, arrow points down). For an endothermic reaction, the products are at a higher energy level than the reactants, with energy absorbed from the surroundings (ΔH is positive, arrow points up).
Must show: Relative positions of reactants and products, Direction of energy change (ΔH), Energy flow (released or absorbed)
Also accept: Accept a labelled diagram instead of text if accurate.
Common mistakes: Reversing energy levels of reactants and products
Show mark scheme and worked solution
Marking points
B1 · 1 mark · States that for exothermic, products are at a lower energy than reactants; for endothermic, products are higher.
B2 · 1 mark · Mentions direction of energy change (ΔH negative or positive, or energy released/absorbed).
B3 · 1 mark · States energy is released to the surroundings in exothermic, absorbed in endothermic.
Worked solution
In an exothermic reaction, the energy profile diagram has the products at a lower energy than the reactants, and ΔH is negative (energy is released to surroundings). In an endothermic reaction, the products are at a higher energy than the reactants, and ΔH is positive (energy is absorbed from the surroundings).