Let's talk about how to make a chemical equation, because they are the main elements of this discipline. Thanks to a deep awareness of all the laws governing the interactions of chemical processes and substances, you can manage them and apply them in various fields of activity.
Theoretical features
The preparation of chemical equations is an important and crucial stage, considered in the eighth grade of secondary schools. What should precede this stage? Before a teacher tells his pupils how to make a chemical equation, it is important to familiarize students with the term “valency”, teach them to determine this value for metals and non-metals, using the periodic table of elements.
Drawing up valency binary formulas
In order to understand how to make a chemical equation for valency, first you need to learn how to make formulas of compounds consisting of two elements, using valency. We offer an algorithm that will help to cope with the task. For example, you need to make a formula of sodium oxide.
First, it is important to consider 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 be oxygen with an oxidation state of -2 (valency 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 valency is constant, it is I.
Oxygen is non-metal, since it is the last in oxide, to determine its valency, we subtract 6 from the eight (number of groups) 6 (the group in which oxygen is located), we obtain that the oxygen valency is equal to II.
Between certain valencies, we find the least common multiple, then divide it by the valency of each of the elements, we obtain their indices. We write the finished formula Na 2 O.
Equation Instructions
Now let's talk more about how to make a chemical equation. First, consider the theoretical points, then move on to specific examples. So, the preparation of chemical equations involves a certain procedure.
- 1st stage. After reading the proposed task, it is necessary 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, an algorithm for compiling formulas of binary compounds, which we considered above, will be required.
- 3rd stage. We check the number of atoms of each element before and after chemical interaction; if necessary, put additional coefficients in front of the formulas.
Combustion Reaction Example
Let's try to figure out how to write the chemical equation of magnesium burning using the algorithm. On the left side of the equation, we write down the sum of magnesium and oxygen. Do not forget that oxygen is a diatomic molecule, therefore it is necessary to put an index of 2. After the equal sign, we make the formula for the product obtained after the reaction. It will be magnesium oxide, in which magnesium is recorded first, and oxygen will be the second in the formula. Further, according to the table of chemical elements, we determine the valency. Magnesium, which is in group 2 (the 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 comply with the law of conservation of mass of substances, it is necessary to set the coefficients. First, 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, the coefficient 2 should be added in the right part in front of the magnesium oxide formula. Next, we consider the number of magnesium atoms before and after the process. The interaction resulted in 2 magnesium, therefore, on the left side in front of a simple substance with magnesium, a coefficient of 2 is also necessary.
The final reaction: 2Mg + O 2 = 2MgO.
Substitution Reaction Example
Any summary in chemistry contains a description of different types of interactions.
Unlike the compound, there will be two substances in the substitution in both the left and right sides of the equation. Suppose you want to write the reaction of interaction between zinc and a solution of hydrochloric acid. The writing algorithm is standard. First, on the left side through the amount we write zinc and hydrochloric acid, on the right side we make the formulas for the resulting reaction products. Since zinc is located up to hydrogen in the electrochemical series of metal stresses, in this process it displaces molecular hydrogen from acid and forms zinc chloride. As a result, we obtain the following record: Zn + HCL = ZnCl 2 + H 2 .
Now we move on to equalizing the number of atoms of each element. Since there was one atom on the left side of chlorine, and after their interaction there were two, a coefficient 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 compendium 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 is that with all the processes that occur between different inorganic or organic substances, you can describe using chemical symbols, signs, coefficients, indices.
How is chemistry different from other sciences? Chemical equations help not only to describe the transformations taking place, but also to carry out quantitative calculations on them, thanks to which it is possible to carry out laboratory and industrial production of various substances.