Beginner Topic 340 of 1102 Thermodynamics & Energetics
Endothermic Reactions
Reactions absorbing heat from the surroundings, with positive enthalpy change.
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In-depth explanation of Endothermic Reactions
An endothermic reaction absorbs heat from its surroundings, so the system's enthalpy change is positive and the surroundings cool down. The products have higher enthalpy than the reactants, because the energy needed to break bonds exceeds the energy released when new bonds form. Endothermic processes are often driven by a large increase in entropy, which can make them spontaneous even though they require heat input. Dissolving ammonium nitrate in water and the photosynthetic conversion of carbon dioxide and water into sugars are familiar endothermic examples, the latter powered by absorbed light energy. Because the temperature of the mixture falls, endothermic reactions are useful in instant cold packs and in some industrial processes.
Going deeper: Endothermic Reactions
Key ideas: Signs to recognize: delta H positive, the surroundings cool and the products are higher in enthalpy. Because they absorb heat, they proceed spontaneously only if the entropy increase is large enough, so higher temperature favors them. Photosynthesis, thermal decomposition and dissolving some salts are typical examples.
Common mistakes and connections: A common mistake is saying that an endothermic reaction cannot be spontaneous, but with delta S positive and enough temperature, delta G becomes negative. Another is confusing a cold container with a reaction that releases cold, when in fact it is absorbing heat. Link this topic to the Gibbs energy discussion.
Visualization of Endothermic Reactions
In an endothermic reaction products lie above reactants, so delta H is positive and heat is absorbed from the surroundings, as when ammonium nitrate dissolves. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Dissolving ammonium nitrate in water has a positive enthalpy of solution, so the solution becomes noticeably colder.
Frequently asked questions about Endothermic Reactions
What is Endothermic Reactions?
Reactions absorbing heat from the surroundings, with positive enthalpy change.
Is Endothermic Reactions a beginner, intermediate or advanced topic?
Endothermic Reactions is a beginner topic in Thermodynamics & Energetics. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Endothermic Reactions?
Study these earlier topics in Thermodynamics & Energetics first: First Law of Thermodynamics, Enthalpy, Exothermic Reactions.
What comes after Endothermic Reactions?
The next topics in Thermodynamics & Energetics are Specific Heat Capacity and Molar Heat Capacity.
Can I practise Endothermic Reactions with quizzes?
Yes. The interactive lesson includes a self-check question on Endothermic Reactions, and the Thermodynamics & Energetics quiz draws on every topic in this area.
Where Endothermic Reactions fits in Thermodynamics & Energetics
Endothermic Reactions is topic 12 of 91 in Thermodynamics & Energetics.