# Advice 1: How to write equation of chemical reactions

The main subject of study in chemistry are reactions between various chemical elements and substances. Deep understanding of the regularities of interaction of substances and processes in chemical reactions gives the possibility to manage and to exploit. A chemical equation is a way of expressing a chemical reaction, which contains formulas of the starting materials and products, the coefficients showing the number of molecules of each substance. Chemical reactions are divided into the reaction of compound, substitution, decomposition, and exchange. Also among them are redox, ionic, reversible and irreversible, exogenous, etc.
Instruction
1
Determine which substances interact with each other in your reaction. Record them in the left side of the equation. For example, consider a chemical reaction between aluminum and sulfuric acid. Place the reagents on the left: Al+H2SO4

Next, place the equal sign, as in a mathematical equation. In chemistry you can meet arrow pointing to the right, or two oppositely directed arrows, "sign of reversibility".

As a result of interaction of metals with acid produce salt and hydrogen. The reaction products write after the equal sign on the right.

Al+H2SO4=Al2(SO4)3+H2

Get the reaction scheme.
2
To make a chemical equation, you need to find the coefficients. In the left part previously obtained schema to the composition of sulphuric acid consists of hydrogen atoms, sulfur and oxygen in the ratio 2:1:4, the right side contains 3 sulfur atom and 12 atoms of oxygen in the composition of salt and 2 hydrogen atoms in the molecule of the gas H2. In the left part of the ratio of these three elements is 2:3:12.
3
To equalize the number of atoms of sulfur and oxygen in sulfate of aluminium(III), put in the left side of the equation before acid ratio 3. Now in the left part six atoms of hydrogen. To equalize the number of elements of the hydrogen, put the coefficient 3 in front of him on the right side. Now the ratio of atoms on both sides equal to 2:1:6.
4
Left to equalize the amount of aluminum. Since the structure of the salt contains two atoms of metal, put the coefficient 2 in front of aluminum on the left side of the diagram.

As a result, you will receive a balanced equation for the reaction of this scheme.

2Al+3H2SO4=Al2(SO4)3+3H2
To check the job, you can use the law of conservation of mass.

# Advice 2: How to write equations of reactions in chemistry

The reaction equation for the conditional entry of a chemical process in which some substances change into different change properties. To write chemical reactions using formulas of the substances and knowledge about the chemical properties of the compounds.
Instruction
1
Correctly write the formula, in accordance with their names. For example, aluminium oxide Al₂O₃, index 3 from aluminum (corresponding to its oxidation number in this compound) put near the oxygen, and the index 2 (oxidation state of oxygen) near the aluminium.
If the degree of oxidation of +1 or -1, the index is not assigned. For example, you need to write down the formula of ammonium nitrate. Nitrate acid residue of nitric acid (-NO₃, S. O. -1), ammonium (-NH₄, p. o. +1). Therefore, the formula of the nitrate of ammonium - NH₄ NO₃. Sometimes the oxidation state is specified in the title compound. Sulfur oxide (VI) - SO₃, silica (II) SiO. Some simple substances (gases) is written with index 2: Cl₂, J₂, F₂, O₂, H₂, etc.
2
You must know which substances react. Visible signs of reaction gas evolution, color change, and sedimentation. Very often, reactions take place without visible changes.
Example 1: neutralization reaction
H₂SO₄ + 2 NaOH → Na₂SO₄ + 2 H₂O
Sodium hydroxide reacts with sulfuric acid to form the soluble salt sodium sulfate and water. The sodium ion is cleaved and connected to the remainder of the acid, replacing the hydrogen. The reaction takes place without external signs.
Example 2: iodoformi sample
SNO + 4 J₂ + 6 NaOH→CHJ₃↓ + 5 NaJ + HCOONa + 5 H₂O
The reaction takes place in several stages. The end result is the deposition of crystals of iodoform yellow color (positive reaction to alcohol).
Example 3:
Zn + K₂SO₄ ≠
The reaction is not possible, because the number of the stress of metals, zinc is second only to potassium and not can displace it from the connections.
3
The law of conservation of mass States that the mass of substances, which entered into reaction is equal to the mass of the resulting substances. Proper recording of chemical reactions is half the battle. You need to place the coefficients. Begin to equalize with those of compounds in the formulas which contain large indexes.
K₂Cr₂O₇ + 14 HCl → 2 CrCl₃ + 2 KCl + 3 Cl₂↑ + 7 H₂O
Arrange the coefficients start with the potassium bichromate, because its formula contains the highest index (7).
Such accuracy in the recording of the reactions required for calculation of mass, volume, concentration, of the released energy and other values. Be careful. Remember the most common formulae of acids and bases, and acidic residues.
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