Exothermic and Endothermic Reactions
Автор: 1234455666 • Октябрь 22, 2024 • Доклад • 458 Слов (2 Страниц) • 17 Просмотры
Lecture Notes: Exothermic and Endothermic Reactions
1. Introduction to Chemical Reactions
- Chemical Reaction: A process where substances (reactants) change to form new substances (products).
- Energy in Reactions: Every chemical reaction involves a change in energy, often in the form of heat.
- This energy change is key to understanding exothermic and endothermic reactions.
2. Exothermic Reactions
Definition: Reactions that release energy, usually in the form of heat, light, or sound. The energy released comes from the chemical bonds of the reactants.
- Example: Combustion of wood, where heat and light are produced.
Characteristics:
- Surrounding temperature increases.
- Reactants have higher energy than products.
- Energy is released to the surroundings.
Key Examples:
- Combustion: Burning of fuels (e.g., natural gas, wood).
- Respiration: The metabolic process in cells that releases energy.
- Neutralization: Acid + base reactions (e.g., HCl + NaOH).
Energy Diagram:
- Reactants → (energy released) → Products
- The products are at a lower energy level than the reactants.
3. Endothermic Reactions
Definition: Reactions that absorb energy from the surroundings. These reactions require energy to proceed, usually in the form of heat.
- Example: Photosynthesis, where plants absorb light energy to convert CO₂ and H₂O into glucose and oxygen.
Characteristics:
- Surrounding temperature decreases.
- Products have higher energy than reactants.
- Energy is taken in from the surroundings.
Key Examples:
- Photosynthesis: Plants absorbing sunlight to produce glucose.
- Dissolving of ammonium chloride in water: The solution cools down as the reaction absorbs heat.
- Thermal decomposition: Breaking down calcium carbonate (CaCO₃) to form calcium oxide (CaO) and CO₂ requires heat.
Energy Diagram:
- Reactants → (energy absorbed) → Products
- The products are at a higher energy level than the reactants.
4. Comparison of Exothermic and Endothermic Reactions
Aspect | Exothermic | Endothermic |
Energy Flow | Energy is released to surroundings | Energy is absorbed from surroundings |
Temperature Change | Surroundings get hotter | Surroundings get cooler |
Energy of Products | Lower than reactants | Higher than reactants |
Examples | Combustion, respiration, neutralization | Photosynthesis, melting ice, thermal decomposition |
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