How to make a chemical reaction equation: a sequence of actions
Let's talk about how to make a chemical reaction equation. This question mainly causes serious difficulties for schoolchildren. Some can not understand the algorithm for compiling product formulas, others incorrectly place the coefficients in the equation. Given that all quantitative calculations are carried out precisely by the equations, it is important to understand the algorithm of actions. Let's try to figure out how to make up the equations of chemical reactions.
Formulating valence formulas
In order to properly record the processes occurring between different substances, you need to learn how to write formulas. Binary compounds are taking into account the valences of each element. For example, in metals of the main subgroups, it corresponds to the group number. In drawing up the final formula, the smallest multiple is determined between these indicators, then the indices are placed.
What is the equation
By it is meant a symbolic record that displays the interacting chemical elements, their quantitative ratios, as well as those substances that are obtained as a result of the process. One of the tasks offered to ninth grade students for final certification in chemistry has the following wording: “Formulate the reaction equations characterizing the chemical properties of the proposed class of substances”. In order to cope with the task, students must have an algorithm of actions.
For example, you need to write the process of burning calcium, using symbols, coefficients, indexes. Let's talk about how to make the equation of a chemical reaction, using the procedure. In the left side of the equation, we write in the "+" signs with the signs of the substance that are involved in this interaction. Since combustion occurs with the participation of air oxygen, which belongs to diatomic molecules, we write its formula O2.
Following the equal sign, we form the composition of the reaction product using the rules of the valence arrangement:
2Ca + O2 = 2CaO.
Continuing the conversation about how to make the equation of a chemical reaction, we note the need to use the law of constancy of composition, as well as preservation of the composition of substances.They allow to carry out the process of adjustment, to arrange the missing coefficients in the equation. This process is one of the simplest examples of interactions occurring in inorganic chemistry.
In order to understand how to make up the equation of a chemical reaction, let us note some theoretical questions concerning this topic. The law of conservation of mass of substances, formulated by M. V. Lomonosov, explains the possibility of the arrangement of coefficients. Since the number of atoms of each element before and after the interaction remains unchanged, it is possible to carry out mathematical calculations.
When equalizing the left and right sides of the equation, the smallest common multiple is used, in the same way as the compound formula is made taking into account the valences of each element.
After schoolchildren have worked out an algorithm of actions, they will be able to create an equation of reactions characterizing the chemical properties of simple substances. Now you can proceed to the analysis of more complex interactions, such as occurring with the change of oxidation states of the elements:
Fe + CuSO4 = FeSO4 + Cu.
There are certain rules according to which the oxidation states are set in simple and complex substances. For example, for diatomic molecules, this indicator is zero, in complex compounds the sum of all oxidation states should also be zero. In the preparation of electronic balance determine the atoms or ions that donate electrons (reducing agent), take them (oxidizer).
Between these indicators is determined by the smallest multiple, as well as coefficients. The final step in the analysis of redox interaction is the distribution of coefficients in the scheme.
One of the important issues that is considered in the course of school chemistry is the interaction between solutions. For example, the task is given as follows: "Make an equation for the chemical reaction of ion exchange between barium chloride and sodium sulfate." It involves writing a molecular, complete, abbreviated ionic equation. To consider the interaction at the ion level, it is necessary to indicate it for each starting material, the reaction product from the solubility table. For example:
BaCl2 + Na2SO4 = 2NaCl + BaSO4
Substances that do not dissolve into ions are recorded in molecular form. The exchange of ions proceeds completely in three cases:
- sediment formation;
- gas release;
- obtaining a low-dissociated substance, for example, water.
If a substance has a stereochemical coefficient, it is taken into account when writing the complete ionic equation. After the complete ion equation has been written, the reduction of those ions that were not bound in solution is carried out. The final result of any task involving the consideration of the process occurring between solutions of complex substances will be a record of the reduced ionic reaction.
Chemical equations allow us to explain with the help of symbols, indices, coefficients those processes that are observed between substances. Depending on which process is going on, there are certain subtleties of writing the equation. The general algorithm for composing reactions, discussed above, is based on the valence, the law of conservation of mass of substances, the constancy of the composition.