🔥 Reactions

Exploring chemical reactions and their mechanisms

What are Chemical Reactions?

Chemical reactions are processes where substances (reactants) are transformed into different substances (products) through the breaking and forming of chemical bonds. These reactions involve changes in energy and often produce observable effects.

Main Idea: Chemical reactions involve the rearrangement of atoms to form new substances with different properties.

Evidence of Chemical Reactions

Color Change

The appearance of a new color or disappearance of an existing color.

Example: Blue litmus turns red in acid

Gas Formation

Bubbles or fizzing indicate gas production.

Example: Baking soda + vinegar

Temperature Change

Reaction mixture gets hotter (exothermic) or colder (endothermic).

Example: Burning wood releases heat

Precipitate Formation

Solid particles form in a liquid solution.

Example: Cloudy solution forms

Odor Change

New smell appears or existing smell disappears.

Example: Food cooking

Light Emission

Glow or light is produced during the reaction.

Example: Glow sticks

Energy Changes in Reactions

Exothermic Reactions

  • • Release energy to surroundings
  • • Feel hot or warm
  • • Energy is a product
  • • Examples: Combustion, neutralization
Reactants → Products + Energy

Endothermic Reactions

  • • Absorb energy from surroundings
  • • Feel cold or cool
  • • Energy is a reactant
  • • Examples: Photosynthesis, melting ice
Reactants + Energy → Products

Reaction Rates

Reaction rate is how fast a reaction occurs. Several factors affect the speed of chemical reactions.

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Temperature

Higher temperature = faster reaction

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Concentration

Higher concentration = faster reaction

🔬

Catalyst

Speeds up reaction without being consumed

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Surface Area

More surface area = faster reaction

Types of Reactions

Combustion Reactions

A substance reacts with oxygen to produce heat and light. Usually involves hydrocarbons.

Fuel + O₂ → CO₂ + H₂O + Energy
Example: CH₄ + 2O₂ → CO₂ + 2H₂O (burning methane)

Double Displacement Reactions

Two compounds exchange ions to form two new compounds. Often produces a precipitate, gas, or water.

AB + CD → AD + CB
Example: AgNO₃ + NaCl → AgCl↓ + NaNO₃

Single Displacement Reactions

One element replaces another element in a compound. More reactive element displaces less reactive one.

A + BC → AC + B
Example: Fe + CuSO₄ → FeSO₄ + Cu

Synthesis Reactions

Two or more simple substances combine to form a more complex compound.

A + B → AB
Example: 2H₂ + O₂ → 2H₂O

Decomposition Reactions

A complex compound breaks down into simpler substances.

AB → A + B
Example: 2H₂O₂ → 2H₂O + O₂

Acid-Base Reactions (Neutralization)

An acid reacts with a base to form a salt and water.

Acid + Base → Salt + Water
Example: HCl + NaOH → NaCl + H₂O

Oxidation-Reduction (Redox)

Reactions involving the transfer of electrons between substances.

Oxidation: Loss of electrons
Reduction: Gain of electrons
Example: 2Na + Cl₂ → 2NaCl (sodium loses electrons, chlorine gains electrons)

Catalysts and Enzymes

Catalysts

  • • Speed up chemical reactions
  • • Not consumed in the reaction
  • • Lower activation energy
  • • Can be recovered unchanged
  • • Examples: Platinum in catalytic converters

Enzymes

  • • Biological catalysts
  • • Made of proteins
  • • Highly specific for substrates
  • • Work best at specific pH and temperature
  • • Examples: Amylase (digests starch)

Reversible vs Irreversible Reactions

Reversible Reactions

  • • Can go both directions
  • • Use double arrows (⇌)
  • • Reach equilibrium
  • • Products can form reactants
  • • Example: N₂ + 3H₂ ⇌ 2NH₃

Irreversible Reactions

  • • Go only in one direction
  • • Use single arrow (→)
  • • Go to completion
  • • Products cannot form reactants
  • • Example: Combustion reactions

Real-World Applications

Cooking

Maillard reaction (browning), caramelization, protein denaturation.

Medicine

Drug metabolism, enzyme reactions, acid-base balance in body.

Industry

Haber process (ammonia), contact process (sulfuric acid), polymerization.

Environment

Photosynthesis, respiration, acid rain formation, ozone depletion.

Energy

Combustion engines, batteries, fuel cells, nuclear reactions.

Daily Life

Rusting, digestion, cleaning products, photography.

Lazy Read

  • • Chemical reactions transform reactants into products
  • • Evidence includes color change, gas formation, temperature change, precipitate
  • • Exothermic reactions release energy, endothermic reactions absorb energy
  • • Reaction rate depends on temperature, concentration, catalysts, surface area
  • • Common types: combustion, acid-base, redox, double displacement, single displacement, synthesis, decomposition
  • • Catalysts speed up reactions without being consumed
  • • Reversible reactions can go both directions, irreversible go to completion
  • • Chemical reactions are essential in everyday life and industry
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