Why is neutralization an exothermic reaction

According to the Brönsted definition, the base is the opposite of an acid and the acid is the opposite of a base. For this reason, the base and acid neutralize each other when they are mixed together. This can be shown using the example of the reaction of hydrochloric acid with sodium hydroxide solution:

The H3O+-Ions in the hydrochloric acid and the OH--Ions in the caustic soda react to form two molecules of water. The second reaction product is sodium chloride. Amazingly, you get two completely harmless substances from two strongly corrosive substances. The neutralization reaction is exothermic and heat is released.
This property can be used when an acid is to be destroyed. According to this principle, the concentration of an unknown acid (or base) can also be determined with the help of a titration. The neutralization point at pH = 7 shows (with equally strong acids and bases) that the H3O+-Ions and the OH--Ions canceled each other out. If you pour concentrated hydrochloric acid and concentrated sodium hydroxide solution together so that the neutralization point is exactly reached, you could even drink the reaction product!

Neutralization of sodium hydroxide solution with hydrochloric acid in a titration
In the stomach of the human body there is gastric juice that is produced by the gastric mucosa. The gastric juice consists of mucus, hydrochloric acid, water and enzymes. The enzymes are particularly important for the digestion of proteins. The hydrochloric acid is responsible for killing bacteria. The gastric mucus with a pH of 1 to 1.5 would attack the stomach wall under normal circumstances. The uppermost cell layer of the stomach wall forms a mucus that is impermeable to acids. The underlying glands produce sodium hydrogen carbonate, which neutralizes the acid that enters.
In the case of stress or constant anger, through the consumption of fatty foods, alcohol or through the intake of drugs that irritate the mucous membrane, the sensitive protective mechanism is disturbed and stomach acid penetrates the mucous membrane. With a one-sided, protein-rich diet in the absence of vegetables and fiber, the body is supplied with too much acid from the breakdown substances of the proteins, which promotes over-acidification in the whole body. The overproduction of acid can lead to inflammation of the stomach lining or gastritis. In people who have the bacterium Helicobacter pylori in the stomach, there is a risk of developing a gastric ulcer. There are some drugs available for gastritis that neutralize stomach acid. This is called an antacid. In the past, soda NaHCO was used for this3 and calcium carbonate CaCO3 used. Both substances neutralize the acid:
NaHCO3 + HCl NaCl + H2O + CO2
CaCO+ 2 HCl CaCl2 + CO2 + H2O
Due to long-term side effects, these drugs are no longer used today. Modern antacids contain magnesium hydroxide or aluminum hydroxide Al (OH)3. Aluminum hydroxide also acts as a buffer and is able to bind the acid over a longer period of time:

Al (OH)3 + 3 HCI AlCl3 + 3 H.2O Al (OH) Cl2 + HCI + 2H2O

additional Information
Titration and dimensional analysis

Create a book individually: Basic text neutralization


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