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Exothermic and Endothermic Reactions

Автор:   •  Октябрь 22, 2024  •  Доклад  •  458 Слов (2 Страниц)  •  17 Просмотры

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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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