Chemical equilibrium

After reading this article, you will learn how the equilibrium of a chemical system is described, further described The principle of Le Chatelier is the influence of external factors on the equilibrium of the system.

Stability of the chemical system

Different molecules interact with each other in different ways depending on environmental conditions, for example, if there is methane and oxygen in the vessel, then gorenje will not occur until a spark is brought to the mixture.:

CH₄ + 2O₂ → CH₄ + 2O₂ (no reaction occurs)
CH₄ + 2O₂ —^spark→ CO₂ + H₂O (methane gorenje)

Stable condition

The stable state of the system means that a chemical reaction cannot occur under normal conditions

Metastable state

Metastable or false equilibrium - a system that may not undergo changes for a long time term, but is excited when certain changes are made (for example, a catalyst or a spark, as in the example with methane above).

Unstable state

A system in which reactions occur so quickly that it is impossible to withstand the conditions under which the system it will be in balance.

Chemical reaction equilibrium

N₂ + 3H₂ ↔ 2NH₃ is a reversible process

Any reaction proceeds until it reaches equilibrium. Balance is a compromise between two opposites trends: the state of minimum energy and the state of greatest entropy. Equilibrium is a dynamic state in which forward and reverse reactions are preserved and have the same speed. State of equilibrium it does not depend on the direction of the reaction.

Any system tends to a state of equilibrium. If external forces are applied to the system in equilibrium, then after after the termination of the impact, the system will return to a state of equilibrium.

If the process is reversible, then both reactions (forward and reverse) proceed at the same speed.

Equilibrium constant K_c

K_c = [C]^c[D]^d/[A]^a[B]^b is the value calculated for reactions aA_(d) + bB_(d) ↔ cC_(d)+ dD_(d)

For a heterogeneous system (a system involving more than one phase), only the gaseous parts are taken into account

CO_{2 (g)} + H_{2 (g)} ↔ CO_(g) +H₂O_(g)
K_c = [CO]/[CO₂][H₂]

The direction of the reaction is calculated based on the initial concentrations: Q = [C₀]^c[D₀]^d/[B₀]^b[A₀]^a. If Q > K_c, then a direct reaction occurs, if Qc, then the reverse occurs reaction ←.

Equilibrium constant K_p

The equilibrium constant expressed in terms of partial pressures of substances K_p = [C]^c/[A]^a

K_p = K_c(RT)^Δn , where Δn is the difference in moles of the amount of products and reagents.

The Le Chatelier principle

If the system in equilibrium is influenced from the outside, then the equilibrium will shift in the direction of compensation external influence.

Effect of concentration

When a substance is added, the reaction shifts towards the absorption of the added substance if the amount is reduced substances, then the reaction will shift towards the formation of a larger amount of substance.

Influence of volume and pressure

If you reduce the volume of the system in equilibrium, then the equilibrium will shift towards a decrease in the total the number of moles of gas, if you increase the volume, then in the direction of increasing the number of moles of the substance. Similarly, with a decrease in pressure, the equilibrium shifts towards an increase in the number of moles of matter, with an increase in pressure, the equilibrium shifts towards a decrease in the number of moles of matter.

But

When an inert gas is added, the pressure of the system increases, but the equilibrium of the system does not change!

Influence of temperature

An increase in temperature forces the course of an endothermic reaction, a decrease - an exothermic one.

In an endothermic reaction, heat is absorbed, in an exothermic reaction, it is released.

The effect of the catalyst

The addition of a catalyst does not change the equilibrium position, but accelerates the establishment of equilibrium.