Five Chemicals that Changed History: Potassium Nitrate

KNO3 (Potassium Nitrate)

The Chemistry

Potassium nitrate is one of the main ingredients in gunpowder. Typical black powder is composed of 75% potassium nitrate, 15% charcoal, and 10% sulfur.





Potassium nitrate oxidizes charcoal and sulfur, which burn fiercely in an exothermic reaction which releases carbon dioxide and nitrogen gas. Here is a simplified reaction of gunpowder.

The History

Potassium nitrate is also known as nitre, or saltpeter. It comprises more than half of the chemicals in gunpowder, with the other part including charcoal and sulfur. Perhaps the most interesting example of nitre in history is in the American Civil War. 




At the beginning of North-South hostilities in April 1861, both the Union and the Confederacy realized that they would need more nitre in order to win a prolonged war. When the Union first blockaded the Confederacy from importing Indian nitre from Britain, the desperate south responded by starting the Nitre Bureau in an all-out campaign to find domestic sources of nitre. At first, the South could only produce 500 pounds of nitre a day from caves in Kentucky and Tennessee, but eventually they were able to produce a ton a day with extensive mining in Texas.

The North had more productive and cost effective methods of obtaining nitre than the South. With the help of chemical magnate Henry DuPont and his son Lammot DuPont, the North imported 2 million pounds of nitre for the U.S. Navy.

The efficient production of nitre was key in the success of the Union in winning the Civil War.

5 Most Famous Chemists: Lavoisier

Hello everyone, apologizes for not posting in a while, as I have been busy with other things during the winter season. I wanted to look at the most famous chemists, who all made huge contributions to science. Enjoy!



Antoine Lavoisier (1743-1794)
Lavoisier was a French chemist, often known as the “father of modern chemistry.” He established the law of conservation of mass, which states that for a closed system, mass does not change. Lavoisier also experimented with phosphorus and sulfur, proving that some elements can exist as gases, liquids, or solids. 

5 Most Famous Chemists: Curie

Marie Curie (1867-1934)

Marie Curie was a Polish and French chemist who pioneered research on radioactivity. She formulated a radioactivity theory and discovered the elements polonium and radium, eventually becoming the first woman to win a Nobel Prize. The unit of radioactivity, the curie (Ci), is named after her. 

5 Most Famous Chemists: Mendeleev

Dmitri Mendeleev (1834-1907)

Mendeleev was a Russian chemist credited for developing the first periodic table. He organized atoms according to atomic weight, discovering a periodicity of properties and eventually arranged atoms into a table that could be used to predict the discovery of several new elements. 

5 Most Famous Chemists: Dalton

John Dalton (1766-1844)

Known as the “father of meteorology”, Dalton is an English chemist known best for his contributions to atomic theory. After studying elements such as carbon, hydrogen, nitrogen, and oxygen, Dalton claimed that atoms of different elements are different in size and mass, forming the foundation of his atomic theory of matter. He is also known for Dalton’s law of partial pressures, which states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the individual gases. 

5 Most Famous Chemists: Avogadro

Amedeo Avogadro (1766-1856)
Avogadro was an Italian chemist most famous for Avogadro’s number, 6.02 x 10²³, the number of elementary particles in a mole. He also theorized Avogadro’s law, which states that “equal volumes of gases at the same temperature and pressure have equal numbers of molecules”. 

Chemistry in Refrigerators

Today, I wanted to explore a topic many of us overlook: how refrigerators work.

The function of refrigerators is based off of two simple concepts:

1. Gases cool when they expand
2. The second law of thermodynamics (heat flows from hot to cold bodies)

Here is a diagram to help explain how it works.





Most modern refrigerators today use a gas called HFC-134a, or tetrafluoroethane, which is stored in the tubes. Here is the cycle of refrigeration.

1. HFC-134a is compressed by the compressor, it heats up. (Pv=nRT, as P increases, T increase.)

2. The gas passes through the tubes outside the refrigerator (red), where it cools and becomes a liquid. The heat is released outside of the refrigerator.

3. The liquid then must pass through the expansion valve, a tiny hole leading to the freezer compartment.

4. Since the pressure is higher in the red tubes than in the blue tubes, the liquid HFC turns into a gas as it moves in the blue tubes.

5. The gas HFC adsorbs the heat in the freezer, and thus the freezer becomes cold.

6. HFC then passes back through the compressor, where a new cycle begins.

Thanks for reading!