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Science

Energy and Thermodynamics

Overview

Students explore the energy changes in chemical reactions, discovering the thermodynamic principles that determine whether a reaction can proceed and in which direction.

Learning Objective
Students understand the concepts of enthalpy, entropy, and Gibbs free energy and can predict whether a reaction will occur spontaneously.

Resources needed

  • None

Lesson stages

0 / 7 done
  1. 1 Recap: chemical reactions either release energy (exothermic) or absorb energy (endothermic).
  2. 2 Introduce enthalpy (H): the total energy content of a system. The change in enthalpy (delta H) is the energy exchanged with the surroundings.
  3. 3 Exothermic reactions: delta H is negative (energy released). Endothermic: delta H is positive (energy absorbed).
  4. 4 Introduce entropy (S): a measure of disorder or randomness in a system. Gases have higher entropy than liquids, which have higher entropy than solids.
  5. 5 The second law of thermodynamics: in a spontaneous process, the total entropy of the universe increases.
  6. 6 Introduce Gibbs free energy: delta G = delta H minus T times delta S. A reaction is spontaneous when delta G is negative.
  7. 7 Apply: a reaction that is exothermic and increases entropy (delta H negative, delta S positive) is always spontaneous. A reaction that is endothermic and decreases entropy is never spontaneous.

Tap a step to mark it as done.

Variations

  • Calculate delta G for a simple reaction at different temperatures.
  • Discuss why ice melts at room temperature despite being an endothermic process (entropy increase drives it).
  • Connect to biology: living things maintain order (low entropy) by constantly using energy.
More information

Teach: enthalpy, entropy, Gibbs free energy, exothermic, endothermic, spontaneous, delta H, delta S, delta G. The equation delta G = delta H minus T delta S is the most important quantitative relationship at this level.

Focus on enthalpy and exothermic/endothermic before introducing entropy and Gibbs free energy.

Can students predict whether a reaction is spontaneous given values of delta H and delta S? Can they explain why some endothermic reactions occur spontaneously?

No resources needed. All calculations require only arithmetic. Draw simple energy diagrams in soil.

Students often think only exothermic reactions are spontaneous. Ice melting is endothermic but spontaneous at room temperature — entropy drives it. This directly challenges the common misconception.

Thermodynamics underpins all of chemistry, engineering, and biology. Understanding why reactions occur spontaneously is essential for understanding metabolism, industrial chemistry, and the direction of all physical processes.

Activity details
Secondary Challenging 30 minutes no prep Whole Class, Small Group Indoor & Outdoor
Topics
Thermodynamics Enthalpy Entropy