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Endothermic reactions are chemical reactions that absorb energy, usually in the form of heat, from their surroundings. This energy intake is essential for the reaction to occur, meaning the system gains energy while the surroundings lose it. As a result, the area around the reaction may feel cooler to the touch.
Examples of common endothermic reactions include:
Photosynthesis: Plants absorb sunlight to convert carbon dioxide and water into glucose and oxygen.
Dissolving ammonium chloride (NH₄Cl) in water: The solution absorbs heat, causing a noticeable cooling effect.
Thermal decomposition reactions: For example, calcium carbonate (CaCO₃) decomposing into calcium oxide (CaO) and carbon dioxide (CO₂) absorbs heat.
Key points about endothermic reactions:
Heat absorption is the defining characteristic.
The products of endothermic reactions usually contain more stored energy than the reactants.
Endothermic reactions are essential in many biological, chemical, and industrial processes, such as cold packs and food processing.
Other options are incorrect:
Heat is evolved → This occurs in exothermic reactions, not endothermic.
Temperature increases → In endothermic reactions, the surroundings may actually cool down, even though the system absorbs energy.
Light is produced → Light emission occurs in some chemical reactions, but it is not a defining feature of endothermic reactions.
In conclusion, the correct answer is Heat is absorbed, as endothermic reactions require energy intake to proceed. Understanding this concept is vital in chemistry, thermodynamics, and practical applications like industrial chemical production and biological energy processes.
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