Theory Exercises

Common Chemistry Reactions in Real Life

Chemistry is everywhere! Here are six essential reactions that shape our daily lives, industry, and history.

First rule to remember: burning a hydrocarbon

In this course, if you are told to burn a hydrocarbon, you should immediately think of a combustion reaction.

  • The reactants are the hydrocarbon and oxygen.
  • In complete combustion, the products are always carbon dioxide and water.
General pattern:
\[\text{Hydrocarbon} + O_2 \rightarrow CO_2 + H_2O\]

If the hydrocarbon is \(C_xH_y\), the complete combustion equation starts like this:

\[C_xH_y + O_2 \rightarrow xCO_2 + \frac{y}{2}H_2O\]

Then you balance the oxygen at the end.

Example:
\[C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O\]

1. The Maillard Reaction

A reaction between amino acids and reducing sugars that gives cooked food its brown color and complex flavor. Reaction:
\[\text{Amino Acids} + \text{Reducing Sugars} \xrightarrow{\text{Heat}} \text{Brown Compounds} + \text{Flavors}\]
  • Examples: Toasted bread, roasted coffee, grilled steak, and caramelized onions.
  • Key Facts: Requires high heat (>150°C/300°F). It is a non-enzymatic browning process.

2. Bronze Formation (Metal Alloy)

Bronze is a metallurgical process where copper and tin are melted together to create a superior material. Composition:
\[\text{88% Copper} + \text{12% Tin} \xrightarrow{\text{Melting}} \text{Bronze}\]
  • Properties: Harder, more durable, and more corrosion-resistant than pure copper.
  • History: Defined the "Bronze Age," used for tools, weapons, and art.
  • Uses: Statues, musical instruments, and ship propellers.

3. Fermentation

A metabolic process where microorganisms break down sugar without oxygen (anaerobic). Reactions:
  • Alcoholic (Yeast): \(\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2\)
  • Lactic Acid (Bacteria): \(\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\text{C}_3\text{H}_6\text{O}_3\)
  • Uses: Bread, yogurt, cheese, wine, beer, and fermented vegetables.
  • Key Facts: Ancient preservation method that works without refrigeration.

4. Saponification

The reaction of fats/oils with a strong base (like NaOH) to produce soap. Reaction:
\[\text{Fat/Oil} + \text{NaOH} \rightarrow \text{Soap} + \text{Glycerol}\]
  • How Soap Works: Molecules have a hydrophobic tail (attracts grease) and a hydrophilic head (attracts water).
  • History: Over 2000 years old, revolutionized hygiene and health.
  • Key Facts: Exothermic and irreversible reaction.

5. Silicon Production from Sand

Silicon is extracted from sand (silicon dioxide) at high temperatures for use in electronics. Main Reaction:
\[\text{SiO}_2 + 2\text{C} \xrightarrow{\text{2000°C}} \text{Si} + 2\text{CO}\]
  • Uses: Computer chips, solar panels, processors, and flexible silicones.
  • Key Facts: Silicon is the 2nd most abundant element in Earth's crust. It is a semiconductor.

6. The Haber-Bosch Process

An industrial reaction that synthesizes ammonia from nitrogen and hydrogen. Reaction:
\[\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3\]
  • Conditions: Requires high pressure, high temperature, and an iron catalyst.
  • Impact: Used for 90% of synthetic fertilizers, feeding ~4 billion people.
  • Uses: Fertilizers, explosives, cleaning products, and refrigerants.