General and Inorganic Chemistry RUDN University General and Inorganic Chemistry

basic concepts of chemistry Molecule is the least particle of substance possessing its chemical properties. Atom is the least particle of a chemical element possessing its chemical properties. Atoms are components of molecules. Chemical element is the kind of atoms characterized by certain set of properties.

basic concepts of chemistry Mole is a unit of measurement of quantity of substances, containing such amount of molecules, atoms or other structural units, as 12 g of an isotope 12С. The number of structural units containing in 1 mole of substances, is known as Avogadro’s number (NA): NA = 6,02×1023 mol-1. The mass of 1 mole of a substance expressed in grams, is called a molar mass of a substance (M, g x mol-1). Quantity of a substance: n = m / M = N / NA (mole).

General laws of Chemistry

General laws of Chemistry

General laws of Chemistry

General laws of Chemistry

General laws of Chemistry The law of equivalents. Substances react with each other in the quantities proportional to their equivalents: n1 = n2 (n – number of equivalents). The equivalent is such a quantity of substance which reacts with 1 mole of hydrogen atoms or replaces them in chemical reactions (the quantity of substance corresponding to a unit valency).

General laws of Chemistry Equivalent mass (МE) is the mass of one equivalent of the substance, expressed in grams: МE = f x M (where f is the factor of equivalence). Calculation of the factor of equivalence of different classes of inorganic compounds: For simple substances and elements in chemical compounds f = 1 / V (where V is the valency of an element). For acids and the bases f = 1 / m (where m is the basidity of an acid or acidity of a base). For oxides and salts f = 1 / n x V (where n is the number of metallic atoms in the compound, and V is the valency of the metal).

General laws of Chemistry

General laws of Chemistry

Chemical KINETICS Rate of a chemical reaction is denoted as number of elementary acts of a reaction which results transformation of reactants into reaction products, in a unit time in a unit volume. In practice, rates of reactions can be measured as a change in concentrations of substances participating in it for a certain time interval:

Chemical KINETICS Law of mass action. Collision of molecules should be a necessary condition for _isinfectio of chemical interaction between molecules. Collision occurs the more often, than more molecules contains in the given volume, i.e. rate of a chemical reaction depends on concentrations of reacting substances.

Chemical KINETICS Temperature dependence of rates of chemical reactions. Rate of a chemical reaction depends on number of effective collisions. Effective collision occurs only between active molecules. Increase in temperature increases number of active molecules, providing them with necessary activation energy, and the rate of the reaction increases. Activation energy is that additional energy which it is necessary to transfer to system to start chemical reaction.

Chemical KINETICS Vant Hoff’s rule. At increase in temperature on 10 ° speed of reaction increases in 2 – 4 times. v2 is the rate of a reaction at temperature T2, v1 is the rate of a reaction at temperature T1,

Chemical KINETICS

Chemical KINETICS In the equilibrium state, reversible reactions are described by an equilibrium constant K: CA, CB, CC, CD are concentrations of gaseous or dissolved substances.

Chemical KINETICS Chemical equilibrium is a dynamic one, so it can be shifted according to le Chateleu’s principle (principle of counteraction): if an equilibrium system is affected by any factor (change in concentrations, pressure or temperature), the equilibrium will be shifted in the direction which weakens the external influence.

The increase in temperature shifts the equilibrium towards an endothermic reaction (the system absorbs heat and increases its internal energy, DH>0), and decrease in temperature shifts the equilibrium towards an exothermic reaction (the system evolves heat and decreases its internal energy, DH <0). The increase in pressure causes shifting of the equilibrium towards less quantity of gaseous substances (as pressure is affected only by gaseous substances), and decrease in pressure shifts the equilibrium towards more quantity of gaseous substances. In case if quantities of gaseous substances among reactants and products are same, change in pressure does not cause shifting of chemical equilibrium. The increase in concentration of one of reactants causes shifting of equilibrium towards formation of products of reaction, and increase in concentration of one of reactional products shifts the equilibrium towards reactants.

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