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12. PHYSICAL AND CHEMICAL PHENOMENA.
EQUATIONS OF CHEMICAL REACTIONS.
From course of natural study and physics you know that to bodies and substances there are changes which share on physical and chemical
PHENOMENA Physical Chemical Physical call such phenomena at which there are no transformations of one substances into others, and their aggregate states, form and the sizes of bodies change.
Primery:plavleniye of ice, wire pulling, granite crushing, water evaporation.Chemical call such phenomena at which there are transformations of one substances into others.
Primery:goreniye of firewood, copper blackening, iron rustiness.
Further we will call the chemical phenomena chemical reactions.Any chemical reaction is followed by external signs on which we also judge its course. It:
1. Emergence of deposit.
2. Discolouration.
3. Gas evolution.
4. Absorption or allocation of warmth.
For course of chemical reaction небходимо several conditions. The first - reduction in contact of reactants; the second - crushing of substances (the greatest crushing is reached by dissolution of substances); the third - for course of many reactions неоходимо heating of reactants to certain temperature.
Chemical reactions can be expressed in writing, by means of the equations of chemical reactions which often call chemical equations. What is it?
The chemical equation is conditional record of chemical reaction by means of chemical formulas and coefficients.
By drawing up the equations of reactions небходимо to use the conservation law of Masa of substances opened by M. V. Lomonosov and A. Lavoisier. The mass of the substances which have reacted is equal to the mass of the substances which have turned out as a result of it. And you know that substances consist of atoms therefore by drawing up chemical equations, we will use правилом:число atoms of each chemical element of mother substances has to equal to number of atoms in reaction products.Algorithm of drawing up equations of reactions.
Let's consider algorithm of drawing up chemical equations on the example of interaction of simple substances: metals and nonmetals with each other. Let phosphorus and oxygen (burning reaction) interact.
1. Write down these substances nearby, between them we put the sign "+" (here we will consider that oxygen diatomic molecule), and after them to the shooter - as equal-sign.
Р + O2
2. We write down reaction product formula after arrow:
Р + O2P2O5
3. From the scheme it is visible that at the left atom oxygen-2, on the right-5, and according to conservation law of mass of substances, the number of atoms of this chemical element has to be identical. To balance their number, we find least common multiple. For 2 and 5 it there will be number 10. We divide naimeshy common multiple into number of atoms in formulas. 10:2=5, 10:5=2, it will also be coefficients, lotory are put respectively before O2 oxygen and oxide of P2O5 phosphorus (V).
Р + 5O22P2O5
oxygen became on 10 at the left and on the right (5·2=10, 2 · 5=10)4. The coefficient belongs to all formula and is put before it. After its statement on the right of phosphorus there were 2·2=4 atoms. And at the left 1 (the coefficient 1 is not put). Means before phosphorus we put coefficient 4.
4P+5O22P2O5
It is also final record of chemical equation.
It is read: four пе plus five about - two equals two pe-two again.
