Theme: Basic consepts of chemical reactions

Types of chemical reactions.
Chemical reactions are classified on the basis of different characteristics. Chemical reactions are classified according to the change in the number of starting substances (reagents) and reaction products involved in the reaction, as well as the change in the number of primary reagents and products. . One new substance is obtained from two or more substances: A + B +… = C;


2H2 + O2 = 2H2O; CaO + CO2 = CaCO3;


In decomposition reactions, several new substances are formed from one substance: C = A + B +…;


2H2O = 2H2 + O2; CaCO3 = CaO + CO2


In substitution reactions, a simple substance replaces a component of a complex substance, resulting in the formation of new simple and complex substances:
AB + C = AC + B;

Zn + 2HCl = ZnCl2 + H2; Fe + CuSO4 = FeSO4 + Cu

Exchange reactions. The components of complex substances are interchangeable: AB + CD = AD + BC


NaOH + HCl = NaCl + H2O BaCl2 + Na2SO4 = BaSO4 + 2NaCl
Exothermic and endothermic reactions can be distinguished depending on the release or absorption of heat (energy) during chemical reactions. The energy released in chemical reactions is called chemical energy. Chemical energy can be converted into heat, light, mechanical, electrical energy. Often chemical energy is converted into heat energy and vice versa. Chemical energy can be converted into heat, light, mechanical, electrical energy. Often chemical energy is converted into heat energy and vice versa. The amount of energy released or absorbed in a chemical reaction is called the thermal effect (Q) of the reaction. kJ). Reactions with the release of heat (energy) are called exothermic (exo-external) reactions. In these reactions, the thermal effect is
indicated by a "+" (plus):

Fe + S = FeS + 96 kJ

S + O2 = SO2 + 297 kJ


Reactions involving the absorption of heat (energy) are called endothermic reactions. In these reactions, the thermal effect is indicated by a "-" (minus) sign.


N2 + O2 = 2NO - 181 kJ;
3O2 = 2O3 - 289