Energy cannot be created or destroyed. However, it can be changed from one form to another. All chemical reactions involve energy changes. Some physical changes also involve energy changes.
In this video, we will give an introduction on exothermic and endothermic changes.
When an endothermic change occurs, heat energy is taken in by the particles from the surroundings. The final substance/product has higher energy than energy of initial substance/reactant.
Physical Process: Evaporation, Melting, Boiling, Dissolving some ionic compounds
Chemical Reaction: Photosynthesis, Thermal Decomposition
When an exothermic change occurs, heat energy is given out by the particles to the surroundings. The final substance/product has lower energy than energy of initial substance/reactant.
Physical Process: Condensation, Freezing, Dissolving anhydrous salts in water, Dissolving acids in water
Chemical Reaction: Combustion, Respiration, Neutralisation, Corrosion of metals
Topic: Energy Changes, O Level Chemistry, Singapore
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