The essence of the chemical reaction. The law of conservation of mass of substances (chemistry)

Chemistry is the science of substances, their structure, properties and their transformation, resulting from chemical reactions, the foundations of which are based on chemical laws. All general chemistry is based on 4 basic laws, many of which were discovered by Russian scientists. But in this article we will talk about the law of conservation of mass of substances, which is included in the basic laws of chemistry.

We consider the law of conservation of mass of matter in detail. The article will describe the history of the discovery of the law, its essence and components.

The law of conservation of mass of matter (chemistry): wording

The mass of substances entering into a chemical reaction is equal to the mass of substances formed as a result of it.

But back to the story. More than 20 centuries ago, the ancient Greek philosopher Democritus suggested that all matter is invisible particles. And only in the XVII century, a chemist of English origin Robert Boyle put forward a theory: all matter is built from the smallest particles of matter. Boyle conducted experiments with metal, heating it on fire. He weighed the vessels before and after heating and noticed that the weight was increasing. The burning of wood gave the opposite effect - ash weighed less than wood.

New story

The law of conservation of mass of substances (chemistry) was granted to the scientific association in 1748 by M.V. Lomonosov, and in 1756 it was testified experimentally. Russian scientist cited evidence. If you heat tightly closed capsules with tin and weigh the capsules before heating, and then after, then the law of conservation of mass of the substance (chemistry) will be obvious. The wording expressed by the scientist Lomonosov is very similar to the modern one. The Russian naturalist made an indisputable contribution to the development of atomic-molecular theory. He combined the law of conservation of mass of substances (chemistry) with the law of conservation of energy. Current doctrine has confirmed these beliefs. And only thirty years later, in 1789, the natural scientist Lavoisier from France confirmed the theory of Lomonosov. But that was just an assumption. It became law in the 20th century (beginning), after 10 years of research by the German scientist G. Landolt.

Examples of experiments

Consider experiments that can confirm the law of conservation of mass of substances (chemistry). Examples:

1. We put red phosphorus in the vessel, cover it tightly with a cork and weigh it. Heat over low heat. The formation of white smoke (phosphorus oxide) indicates that a chemical reaction has occurred. Weigh in again and make sure that the weight of the vessel with the obtained substance has not changed. Reaction equation: 4P + 3O2 = 2P2O3.
2. We take two vessels of Landolt. In one of them, carefully, so as not to mix, we fill in the reagents of lead nitrate and potassium iodide. In another vessel we place potassium thiocyanate and iron chloride. Vessels tightly close. The scales must be balanced. Mix the contents of each vessel. In one, a yellow precipitate forms - this is lead iodide, in the other, iron redanide is obtained in a dark red color. With the formation of new substances, the balance remained balanced.
3. Light a candle and put it in a container. Hermetically close this container. We bring the balance into equilibrium. When the air runs out in the tank, the candle goes out, the chemical reaction process ends. The balance will be balanced, so the weight of the reagents and the weight of the resulting substances are the same.
4. Let's conduct another experiment and consider the law of conservation of mass of substances (chemistry) as an example. The formula of calcium chloride is CaCl2, and sulfate acid is H2SO4. When these substances interact, a white precipitate is formed - calcium sulfate (CaSO4), and hydrochloric acid (HCl). For experience, we need a scale and a Landolt vessel. Very carefully pour calcium chloride and sulfate acid into the vessel, without mixing them, tightly close the cork. Weigh on the scales. Then we mix the reagents and observe that a white precipitate (calcium sulfate) precipitates. This indicates that a chemical reaction has occurred. Weigh the vessel again. Weight remained the same. The equation of this reaction will look like this: CaCl2 + H2SO4 = CaSO4 + 2HCl.

Main

The main goal of a chemical reaction is to destroy molecules in certain substances and subsequently form new molecules of matter. In this case, the number of atoms of each substance before and after the interaction remains unchanged. When new substances are formed, energy is released, and when they decay with its absorption, there is an energy effect that manifests itself in the form of absorption or release of heat. During a chemical reaction, the molecules of the starting materials, the reactants, break down into atoms, from which the products of the chemical reaction are then obtained. The atoms themselves remain unchanged.

The reaction can last for centuries, but can occur rapidly. In the manufacture of chemical products, you need to know the speed of a particular chemical reaction, with the absorption or release of temperature, it passes, what pressure is needed, the amount of reagents and catalysts. Catalysts are a small substance by weight that does not participate in a chemical reaction, but significantly affects its speed.

How to make chemical equations

Knowing the law of conservation of mass of substances (chemistry), we can understand how to correctly compose chemical equations.

1. You need to know the formulas of the reagents that enter into the chemical reaction, and the formulas of the products that result from it.
2. On the left are written the formulas of the reagents, between which the “+” sign is placed, and on the right - the formulas of the resulting products with the “+” sign between them. Between the formulas of the reagents and the resulting products put a sign "=" or arrow.
3. The number of atoms of all components of the reactants should be equal to the number of atoms of the products. Therefore, the coefficients that are put before the formulas are calculated.
4. It is forbidden to move formulas from the left side of the equation to the right or to change their places.

The meaning of the law

The law of conservation of mass of substances (chemistry) made it possible for an interesting subject to develop as a science. Find out why.

• The great importance of the law of conservation of mass of substances in chemistry is that chemical calculations for industry are made on its basis. Suppose you want to get 9 kg of copper sulfide. We know that the reaction of copper and sulfur occurs in mass ratios of 2: 1. According to this law, during the chemical reaction of copper weighing 1 kg and sulfur weighing 2 kg, copper sulfide weighing 3 kg is obtained. Since we need to get copper sulfide weighing 9 kg, that is, 3 times more, then we will need 3 times more reagents. That is 6 kg of copper and 3 kg of sulfur.
• The ability to make the right chemical equations.

Conclusion

After reading this article, there should be no questions about the essence of this law of the history of its discovery, to which, by the way, our famous compatriot, the scientist M.V. Lomonosov. Which again confirms how great is the power of patriotic science. It also became clear the significance of the discovery of this law and its meaning. And those who did not understand how to write chemical equations at school, after reading the article, should learn or remember how to do it.