In order to figure out how to equalize the chemical equation, first you need to find out the purpose of this science.

Definition

Chemistry studies substances, their properties, and transformations. If there is no change in color, precipitation, or release of a gaseous substance, then no chemical interaction occurs.

For example, when filing an iron nail, the metal simply turns into powder. In this case, no chemical reaction occurs.

The calcination of potassium permanganate is accompanied by the formation of manganese oxide (4), the evolution of oxygen, that is, an interaction is observed. In this case, a completely natural question arises of how to correctly equalize the chemical equations. Let's analyze all the nuances associated with such a procedure.

Specificity of chemical transformations

Any phenomena that are accompanied by a change in the qualitative and quantitative composition of substances are classified as chemical transformations. In molecular form, the combustion of iron in the atmosphere can be expressed using signs and symbols.

Odds placement method

How to equalize coefficients in chemical equations? The high school chemistry course deals with the electronic balance method. Let's take a closer look at the process. To begin with, in the initial reaction, it is necessary to arrange the oxidation states for each chemical element.

There are certain rules by which they can be determined for each element. In simple substances, the oxidation state will be zero. In binary compounds, for the first element, it is positive, corresponding to the highest valency. For the latter, this parameter is determined by subtracting the group number from eight and has a minus sign. Formulas consisting of three elements have their own nuances in calculating oxidation states.

For the first and last element, the order is similar to the definition in binary compounds, and an equation is drawn up to calculate the central element. The sum of all indicators must be zero, based on this, the indicator for the average element of the formula is calculated.

Let's continue talking about how to equalize chemical equations using the electronic balance method. After the oxidation states have been set, it is possible to determine those ions or substances that, in the course of chemical interaction, have changed their value.

The plus and minus signs must indicate the number of electrons that were received (given away) in the process of chemical interaction. The smallest common multiple is found between the numbers obtained.

When dividing it into received and given electrons, coefficients are obtained. How to equalize a chemical equation? The numbers obtained in the balance sheet must be put in front of the corresponding formulas. A prerequisite is to check the amount of each element on the left and right sides. If the odds are placed correctly, their number should be the same.

The law of conservation of mass of substances

When discussing how to equalize a chemical equation, it is this law that must be used. Considering that the mass of those substances that have entered into a chemical reaction is equal to the mass of the resulting products, it becomes possible to set coefficients in front of the formulas. For example, how to equalize the chemical equation if simple substances calcium and oxygen interact, and after the completion of the process, an oxide is obtained?

To cope with this task, it is necessary to take into account that oxygen is a diatomic molecule with a covalent non-polar bond, therefore its formula is written in the following form - О2. On the right side, when composing calcium oxide (CaO), the valences of each element are taken into account.

First you need to check the amount of oxygen in each side of the equation, as it is different. According to the law of conservation of mass of substances, a factor of 2 must be put in front of the product formula. Next, the calcium is checked. In order for it to be equalized, we put the coefficient 2 in front of the original substance. As a result, we get the record:

• 2Ca + O2 = 2CaO.

Analysis of the reaction using the electronic balance method

How do you balance chemical equations? RIA examples will help answer this question. Suppose that it is necessary to arrange the coefficients in the proposed scheme using the electronic balance method:

• CuO + H2 = Cu + H2O.

To begin with, for each of the elements in the initial substances and products of interaction, we will arrange the values ​​of the oxidation states. We get the following form of the equation:

• Cu (+2) O (-2) + H2 (0) = Cu (0) + H2 (+) O (-2).

Indicators have changed for copper and hydrogen. It is on their basis that we will compile an electronic balance:

• Cu (+2) + 2е = Cu (0) 1 reducing agent, oxidation;
• H2 (0) -2e = 2H (+) 1 oxidizing agent, reduction.

Based on the coefficients obtained in the electronic balance, we obtain the following record of the proposed chemical equation:

• CuO + H2 = Cu + H2O.

Let's take another example that involves setting odds:

• H2 + O2 = H2O.

In order to equalize this scheme on the basis of the law of conservation of substances, it is necessary to start with oxygen. Considering that a diatomic molecule entered into the reaction, it is necessary to put a coefficient of 2 in front of the formula for the interaction product.

• 2H2 + O2 = 2H2O.

Conclusion

Based on the electronic balance, you can arrange the coefficients in any chemical equations. Graduates of the ninth and eleventh grades of educational institutions who choose an exam in chemistry are offered similar tasks in one of the tasks of the final tests.

To describe the ongoing chemical reactions, equations of chemical reactions are drawn up. In them, to the left of the equal sign (or arrows →), the formulas of the reagents (substances that enter into the reaction) are written, and to the right are the reaction products (substances that are obtained after a chemical reaction). Since we are talking about an equation, the number of atoms on the left side of the equation should be equal to what is on the right. Therefore, after drawing up a diagram of a chemical reaction (recording reagents and products), the coefficients are substituted in order to equalize the number of atoms.

The coefficients are numbers in front of the formulas of substances, indicating the number of molecules that react.

For example, suppose hydrogen gas (H 2) reacts with oxygen gas (O 2) in a chemical reaction. The result is water (H 2 O). Reaction scheme will look like this:

H 2 + O 2 → H 2 O

On the left there are two hydrogen and oxygen atoms, and on the right there are two hydrogen atoms and only one oxygen. Suppose that as a result of the reaction for one hydrogen molecule and one oxygen, two water molecules are formed:

H 2 + O 2 → 2H 2 O

Now the number of oxygen atoms before and after the reaction is equalized. However, the amount of hydrogen before the reaction is half as much as after. It should be concluded that the formation of two water molecules requires two hydrogen molecules and one oxygen. Then you get the following reaction scheme:

2H 2 + O 2 → 2H 2 O

Here, the number of atoms of different chemical elements is the same before and after the reaction. This means that this is no longer just a reaction scheme, but reaction equation... In reaction equations, the arrow is often replaced with an equal sign to emphasize that the number of atoms of different chemical elements is equal:

2H 2 + O 2 = 2H 2 O

Consider this reaction:

NaOH + H 3 PO 4 → Na 3 PO 4 + H 2 O

After the reaction, phosphate was formed, which includes three sodium atoms. Let's equalize the amount of sodium before the reaction:

3NaOH + H 3 PO 4 → Na 3 PO 4 + H 2 O

The amount of hydrogen before the reaction is six atoms (three in sodium hydroxide and three in phosphoric acid). After the reaction, there are only two hydrogen atoms. Dividing six by two makes three. This means that the number three must be placed in front of the water:

3NaOH + H 3 PO 4 → Na 3 PO 4 + 3H 2 O

The number of oxygen atoms before and after the reaction is the same, which means that further calculation of the coefficients can be omitted.

Write down a chemical equation. As an example, consider the following reaction:

• C 3 H 8 + O 2 -> H 2 O + CO 2
• This reaction describes the combustion of propane (C 3 H 8) in the presence of oxygen to form water and carbon dioxide (carbon dioxide).

Write down the number of atoms for each element. Do this for both sides of the equation. Note the subscripts next to each element to determine the total number of atoms. Write down the symbol for each element in the equation and note the corresponding number of atoms.

• For example, on the right side of the equation under consideration, as a result of addition, we get 3 oxygen atoms.
• On the left side we have 3 carbon atoms (C 3), 8 hydrogen atoms (H 8) and 2 oxygen atoms (O 2).
• On the right side we have 1 carbon atom (C), 2 hydrogen atoms (H 2) and 3 oxygen atoms (O + O 2).

Reactions between different kinds of chemicals and elements are one of the main subjects of study in chemistry. To understand how to compose the reaction equation and use them for your own purposes, you need a fairly deep understanding of all the laws governing the interaction of substances, as well as processes with chemical reactions.

Drawing up equations

One way of expressing a chemical reaction is a chemical equation. It records the formula of the initial substance and the product, coefficients that show how many molecules each substance has. All known chemical reactions are divided into four types: substitution, combination, exchange and decomposition. Among them are: redox, exogenous, ionic, reversible, irreversible, etc.

Learn more about how to write chemical equations:

1. It is necessary to determine the name of the substances interacting with each other in the reaction. We write them on the left side of our equation. As an example, consider the chemical reaction that formed between sulfuric acid and aluminum. Place the reagents on the left: H2SO4 + Al. Next, we write the "equal" sign. In chemistry, you can see the sign "arrow", which points to the right, or two oppositely directed arrows, they mean "reversibility." The result of the interaction of a metal and an acid is salt and hydrogen. Write down the products obtained after the reaction after the "equal" sign, that is, on the right. H2SO4 + Al = H2 + Al2 (SO4) 3. So, we see the scheme of the reaction.
2. To draw up a chemical equation, it is imperative to find the coefficients. Let's go back to the previous scheme. Let's look at the left side of it. The composition of sulfuric acid contains atoms of hydrogen, oxygen and sulfur, in an approximate ratio of 2: 4: 1. On the right side there are 3 sulfur atoms and 12 oxygen atoms in the salt. Two hydrogen atoms are contained in a gas molecule. On the left, the ratio of these elements is 2: 3: 12
3. To equalize the number of oxygen and sulfur atoms, which are in the composition of aluminum (III) sulfate, it is necessary to put a coefficient 3 in front of the acid in the left side of the equation. Now we have 6 hydrogen atoms on the left side. In order to equalize the number of elements of hydrogen, you need to put 3 in front of hydrogen on the right side of the equation.
4. Now all that remains is to equalize the amount of aluminum. Since the salt contains two metal atoms, then on the left side in front of aluminum we set the coefficient 2. As a result, we get the reaction equation of this scheme: 2Al + 3H2SO4 = Al2 (SO4) 3 + 3H2

Having understood the basic principles of how to compose the equation for the reaction of chemicals, in the future it will not be difficult to write down any, even the most exotic, from the point of view of chemistry, reaction.

Let's talk about how to make a chemical equation, because they are the main elements of this discipline. Thanks to a deep understanding of all the laws of interactions and substances, you can control them, apply them in various fields of activity.

Theoretical features

The compilation of chemical equations is an important and crucial stage, considered in the eighth grade of general education schools. What should precede this stage? Before the teacher tells his pupils how to make a chemical equation, it is important to acquaint schoolchildren with the term "valence", to teach them to determine this value for metals and non-metals, using the periodic table of elements.

Drawing up binary formulas for valence

In order to understand how to draw up a chemical equation for valency, you first need to learn how to draw up formulas for compounds consisting of two elements using valence. We offer an algorithm that will help to cope with the task. For example, you need to create a formula for sodium oxide.

First, it is important to take into account that the chemical element that is mentioned last in the name should be in the first place in the formula. In our case, the first will be written in the formula sodium, the second oxygen. Recall that oxides are binary compounds in which the last (second) element must necessarily be oxygen with an oxidation state of -2 (valence 2). Further, according to the periodic table, it is necessary to determine the valencies of each of the two elements. For this, we use certain rules.

Since sodium is a metal that is located in the main subgroup of group 1, its valence is unchanged, it is I.

Oxygen is a non-metal, since it is the last in the oxide, to determine its valence, we subtract 6 from eight (the number of groups) (the group in which oxygen is located), we get that the oxygen valence is II.

We find the least common multiple between certain valencies, then divide it by the valence of each of the elements, and obtain their indices. We write the finished formula Na 2 O.

Equation Instructions

Now let's talk in more detail about how to make a chemical equation. First, we will consider the theoretical points, then move on to specific examples. So, drawing up chemical equations involves a certain course of action.

• 1st stage. After reading the proposed task, you need to determine which chemicals should be present on the left side of the equation. A "+" sign is placed between the original components.
• 2nd stage. After the equal sign, it is necessary to formulate the reaction product formula. When performing such actions, you will need an algorithm for compiling formulas for binary compounds, which we discussed above.
• 3rd stage. We check the number of atoms of each element before and after the chemical interaction, if necessary, put additional coefficients in front of the formulas.

Combustion reaction example

Let's try to figure out how to create a chemical equation for the combustion of magnesium using an algorithm. On the left side of the equation, we write in terms of the sum of magnesium and oxygen. Do not forget that oxygen is a diatomic molecule, therefore, it must have an index 2. After the equal sign, we compose the formula of the product obtained after the reaction. It will be in which magnesium is written first, and oxygen is the second in the formula. Further, according to the table of chemical elements, we determine the valencies. Magnesium, which is in group 2 (main subgroup), has a constant valency II, for oxygen, by subtracting 8 - 6, we also obtain valency II.

The process record will look like: Mg + O 2 = MgO.

In order for the equation to correspond to the law of conservation of mass of substances, it is necessary to arrange the coefficients. First, we check the amount of oxygen before the reaction, after the completion of the process. Since there were 2 oxygen atoms, and only one was formed, on the right side, before the magnesium oxide formula, it is necessary to add a factor of 2. Next, we calculate the number of magnesium atoms before and after the process. As a result of the interaction, 2 magnesium was obtained, therefore, on the left side in front of the simple substance magnesium, a coefficient of 2 is also required.

The final form of the reaction: 2Mg + O 2 = 2MgO.

An example of a substitution reaction

Any chemistry synopsis contains a description of different types of interactions.

In contrast to the compound, there will be two substances in the substitution both on the left and on the right side of the equation. Let's say it is necessary to write the reaction of interaction between zinc and we use the standard writing algorithm. First, on the left side, through the sum, we write zinc and hydrochloric acid, on the right side we compose the formulas for the reaction products obtained. Since in the electrochemical series of metal voltages zinc is located before hydrogen, in this process it displaces molecular hydrogen from the acid, forms zinc chloride. As a result, we get the following record: Zn + HCL = ZnCl 2 + H 2.

Now let's move on to equalizing the number of atoms of each element. Since there was one atom on the left side of chlorine, and after the interaction there were two of them, a factor of 2 must be put in front of the hydrochloric acid formula.

As a result, we obtain a ready-made reaction equation corresponding to the law of conservation of mass of substances: Zn + 2HCL = ZnCl 2 + H 2.

Conclusion

A typical chemistry synopsis necessarily contains several chemical transformations. Not a single section of this science is limited to a simple verbal description of transformations, processes of dissolution, evaporation, everything is necessarily confirmed by equations. The specificity of chemistry lies in the fact that all processes that occur between different inorganic or organic substances can be described using coefficients, indices.

How else is chemistry different from other sciences? Chemical equations help not only describe the transformations taking place, but also carry out quantitative calculations based on them, thanks to which it is possible to carry out laboratory and industrial production of various substances.