Beginner Topic 339 of 1102 Thermodynamics & Energetics
Exothermic Reactions
Reactions releasing heat to the surroundings, with negative enthalpy change.
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In-depth explanation of Exothermic Reactions
An exothermic reaction is one in which the system releases heat into its surroundings, so the enthalpy change delta H is negative. The products have lower enthalpy than the reactants, and the energy difference appears as thermal energy that warms the environment. Exothermic behavior occurs when the bonds formed in the products are stronger, and therefore release more energy, than the bonds broken in the reactants. Combustion of fuels, neutralization of acids by bases, and many oxidation reactions are exothermic. Recognizing an exothermic process matters for safety, because the heat released can accelerate the reaction and cause a runaway temperature rise.
Going deeper: Exothermic Reactions
Key ideas: Signs to recognize: delta H is negative, the surroundings warm and the products are lower in enthalpy. Energy-level diagrams slope downward from reactants to products. The released heat can be calculated from n times delta H and is often measured through the temperature rise of water.
Common mistakes and connections: It is wrong to say exothermic reactions need no activation energy, since many need a spark or heat to start, such as burning paper. Also, exothermic does not mean fast. Strongly exothermic reactions carried out in bulk can overheat and become dangerous, which links the topic to reaction engineering and safety.
Visualization of Exothermic Reactions
In an exothermic reaction products lie below reactants, so delta H is negative and heat is released to the surroundings, as in the burning of methane. The interactive lesson shows this as a live animation or chart.
Worked example and use case
A self-heating hand warmer based on the oxidation of iron releases heat as it reacts with oxygen in air.
Frequently asked questions about Exothermic Reactions
What is Exothermic Reactions?
Reactions releasing heat to the surroundings, with negative enthalpy change.
Is Exothermic Reactions a beginner, intermediate or advanced topic?
Exothermic 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 Exothermic Reactions?
Study these earlier topics in Thermodynamics & Energetics first: Internal Energy, First Law of Thermodynamics, Enthalpy.
What comes after Exothermic Reactions?
The next topics in Thermodynamics & Energetics are Endothermic Reactions and Specific Heat Capacity.
Can I practise Exothermic Reactions with quizzes?
Yes. The interactive lesson includes a self-check question on Exothermic Reactions, and the Thermodynamics & Energetics quiz draws on every topic in this area.
Where Exothermic Reactions fits in Thermodynamics & Energetics
Exothermic Reactions is topic 11 of 91 in Thermodynamics & Energetics.