According to one of the classifications used to describe chemical processes, there are two types of opposite reactions - reversible and
irreversible. A reversible reaction does not reach the end, i.e. not one of the substances that entered it is completely consumed and does not change the concentration. Such a process ends with the establishment of a balance or chemical equilibrium, which ⇌ stands for. But the direct and reverse reactions go further without stopping; therefore, the equilibrium is called dynamic or mobile. The onset of chemical equilibrium suggests that the direct reaction occurs at the same rate (V1) as the reverse (V2), V1 = V2. If the pressure and temperature are constant, then the equilibrium in this system can last indefinitely.
Quantitatively, chemical equilibrium is described by an equilibrium constant, which is equal to the ratio of the direct (K1) and inverse (K2) reaction constants. It can be calculated by the formula: K = K1 / K2. The indices of the equilibrium constant will depend on the composition of the reacting substances and temperature.
The shift of the chemical equilibrium occurs according to the Le Chatelier principle, which reads as follows: “If the system, which is in equilibrium, is affected by external factors, then the equilibrium is violated and will shift to the side opposite to this change.”
Consider chemical equilibrium and conditions for its displacement by the example of the formation of an ammonia molecule: N2 + 3H2 ↔ 2NH3 + Q.
Considering the equation of this reaction, we establish:
a direct reaction is a reaction of a compound, because of 2 simple substances, 1 compound (ammonia) is formed, and the reverse is decomposition;
the direct reaction proceeds with the formation of heat, therefore it is exothermic, therefore, the reverse is endothermic and occurs with the absorption of heat.
Now we consider this equation subject to the modification of certain parameters:
Change in concentration. If we increase the concentration of the initial substances — nitrogen and hydrogen — and reduce the amount of ammonia, then the equilibrium will shift to the right to form NH3. If you need to move it to the left, increase the concentration of ammonia.
An increase in temperature will shift the equilibrium towards the reaction, in which heat is absorbed, and when it is reduced, it is released. Therefore, if the temperature is increased during the synthesis of ammonia, then the equilibrium will shift toward the starting products, i.e. to the left, and when the temperature decreases, to the right, towards the reaction product.
If you increase the pressure, the equilibrium will shift to the side where the amount of gaseous substances is less, and when the pressure decreases, to the side where the amount of gas increases. In the synthesis of NH3 from 4 mol of N2 and 3H2, 2 NH3 is obtained. Therefore, if you increase the pressure, the equilibrium will move to the right, to the formation of NH3. If the pressure is reduced, then the equilibrium will shift towards the starting products.
We conclude that chemical equilibrium can be disturbed if you increase or decrease:
temperature
pressure;
concentration of substances.
When a catalyst is introduced into any reaction, the balance does not change, i.e. chemical equilibrium is not disturbed.