Pressure In Dynamic Equilibrium: 7 Facts You Should Know

Pressure is the vertical force per unit area, and dynamic equilibrium is when the body remains in the state of motion covered by the impact of a few forces; then, the body is called the dynamic equilibrium. The termination force portrayed on the body should be zero.

Pressure in dynamic equilibrium is defined as “the position of equilibrium would start hence that the pressure is diminished again. Pressure is created by gas molecules striking the edges of the container. The higher molecules we have in the container, the greater the pressure. If the pressure is expanded, the equilibrium position starts in the supervision of the minimum moles of gas”.

Does pressure affect dynamic equilibrium?

Yes, the pressure affects dynamic equilibrium. When there is intensification in pressure, the equilibrium will displace upon the side of the chemical action with limited moles of gas. When there is the de-intensification in pressure, the equilibrium will displace upon the side of the reaction with unlimited moles of gas.

Increasing the pressure budge the equilibrium position to the edge with the certain molecules. Expanding pressure lowers the influence of the deviation because the pressure reduces as the number of molecules reduces. Decreasing the pressure budge the equilibrium to the edge with the additional molecules.

According to Le Chatelier’s principle, the arrangement or system at equilibrium will acclimate to ease strain when there are variations in the assiduity of reactants or products, the inadequate pressure of constituents, the volume of the arrangement, and the temperature of reaction vary the reaction system.

How does the pressure affect the dynamic equilibrium?

Le Chatelier’s principle described that if a system is at equilibrium that is subordinated to a variation in pressure, temperature, or concentration, in this situation, the dynamic equilibrium budge again, diminishing and preventing the effect of variation.

There is no influence of the pressure suppose if the number of moles of gaseous catalysts and output is a dynamic equilibrium. Although, it distinct the complete quantity of moles of gaseous catalysts and a complete number of moles of gaseous outputs. The certain quantity of moles per unit volume also enlarges on enlarging the pressure, conducting the displacement in the dynamic equilibrium direction.

In this situation, suppose the absolute numbers of moles of products are higher when compared to the absolute number of moles of stimulants. In that case, the low pressure will again esteem progressive reaction. If the quantity of moles of catalysts is greater when compared to the output, elevated pressure will admire the growing reaction.

What will happen if the pressure on the system is increased?

If the external pressure of the system increases, then the volume would also decrease, and the system’s temperature increases because work carried out on the system is done, which increases the enthalpy or internal energy of the system. Suppose the system’s internal pressure increases because the molecules’ kinetic energy increases. Consequently, the number of concussions per unit area would be increased. Therefore, pressure will be increased.

For example, let us contemplate the equilibrium: [latex]H_{2}(g)+I_{2}(g)\rightleftharpoons 2HI(g)[/latex]

This equation consists of two moles of the gaseous molecule on all sides. When the pressure increases, the equilibrium’s position is not changed.

Let us take another example and examine the equilibrium: [latex]H_{2}(g)+3H_{2}(g)\rightleftharpoons 2HI(g)[/latex]

This equation consists of four moles of molecules of the gas on the leftward and two molecules of the gas on the rightward. Suppose if the pressure increased, the system’s equilibrium position was displaced towards the rightward in sequence to decrease the number of gas molecules.

How do you find the dynamic equilibrium pressure?

Dynamic equilibrium pressure includes physical rather than chemical activity. Consider the example of equilibrium between the liquid and the vapor in a sealed container.

Pressure in dynamic eqilibrium
Equilibrium between the liquid and the vapor sealed in the container image credit: pixabay

Rearranging PV = nRT to get

P =[latex]\frac{n}{V\times RT}[/latex] =cRT                  1

Since c= quantity of substance per unit volume = [latex]\frac{n}{V}[/latex] . Thus if the pressure is constant at a given temperature, the assiduity should be constant. The above equation relates the equilibrium constant to pressure. Consider water as an example; for this case, the dynamic equilibrium reaction is given by:

[latex]H_{2}O(I)\rightleftharpoons H_{2} O (g)[/latex]

Kc =[ H2O(g)]

Substituting for the concentration of water vapour from equation 1, we get


In normal case, it is more useful to demonstrate the equilibrium law for gases in terms of pressure instead of in terms of assiduity is,

[latex]aA(g) + bB(g) \rightleftharpoons cC(g)+ dD(g)[/latex]

The pressure dynamic equilibrium constant Kp is described by the relationship.

Kp= PCcPDd/PAaPBb                         2

Where PA is the pressure of the substituent A and PB is the pressure of the substituent B, etc., PA = [A]×RT and PB = [B]×RT.

By using equation 2, we can find the dynamic equilibrium pressure.

How is dynamic equilibrium related to vapor pressure?

The vaporization rate is not zero; hence the vapor pressure creates up to the point where the rate of vaporization and consolidation are equal. At this stage, the web is in dynamic equilibrium, and the low vapor pressure in the barrel is identical to the liquid-vapor pressure.

For example, if we assume keeping a pure liquid in a secured barrel, the vapor pressure is primarily near zero. As a consequence, the rate of consolidation is also near zero. The dehydration grade is not zero. Hence the vapor pressure composes up to the stage where the grade of dehydration and amalgamation are identical.

pressure in dynamic equilibrium
Liquid in a secured barrel image credit: pixabay

At this stage, the arrangement is in dynamic equilibrium, and the little vapor pressure in the barrel equals the equilibrium liquid vapor pressure.

Under what conditions does pressure not influence the equilibrium state?

According to Le Chatelier’s principle, the variation in the pressure should not impact the equilibrium of those reactions that encompass no dissimilarities in the number of moles of products and reactants. It is the condition in the pressure does not influence the equilibrium state.

When the number of atoms segregating and moving products equals the number of atoms segregating and moving to stimulants, you will accomplish the state of equilibrium. If the system’s pressure incorporating gaseous stimulants or products is varied, then equilibrium might be constrained.

pressure in dynamic equilibrium
Number of atoms segregation image credit: pixabay

Consider the example [latex]H_{2}(g)+I_{2}(g)\rightleftharpoons 2HI(g)[/latex]

Number of moles of product = 2

Number of moles of stimulant = 1+1 = 2

Total change = 2-2 = 0

In this equation, stimulants have 2 moles, and products also have 2 moles. So, the variation in pressure does not influence the equilibrium reaction. Theoretically, if the pressure increases, you have an equal number of moles to backslide; hence no variation happens.

Give an example of pressure in dynamic equilibrium?

A bottle of cool fizzy drink is an example of pressure in dynamic equilibrium. This bottle containing the carbon dioxide diffused in the liquid has a certain value. But if you streamed out fifty percent of the liquid and further closed up the bottle, then in this situation, carbon dioxide would be left the liquid state at their rate hold on reducing and at the same instant pressure of the gaseous state goes on enlarging and they attain the equilibrium state.

presure in dynamic equilibrium
Cool fizzy drink image credit: Pixabay

Because of isothermal motion, a carbon dioxide molecule might be left in the liquid state. Still, within a less period, another carbon dioxide molecule would be moved from the gas to the liquid, and contrariwise. When equilibrium is attained, the rate of budge of carbon dioxide from gas to liquid.

When an object retains the translational or rotational motion because of the effect of the employed forces, then the object is said to be in dynamic equilibrium; for example, a raindrop grasping the earth with a stable velocity is in dynamic equilibrium.

Most frequently asked questions.

What is equilibrium? Mention the types of equilibrium?

Equilibrium is defined as “a state of steadfastness between the reversing forces that are neither static (as in an object simulated by forces whose end product is zero) nor dynamic (as in an opposable chemical reaction when the velocities in the two supervisions are identical): a state of rational or demonstrative balance”.

There are three types of equilibrium namely.

A stable equilibrium is when an object is moderately replaced by equilibrium and leans to rebound against equilibrium. Then, it is called stable equilibrium.

1. Unstable equilibrium

It is called unstable equilibrium when the body is replaced from equilibrium and leans to draw away from the equilibrium position.

1. Neutral equilibrium

When a body is replaced from equilibrium and no force is performed on the body, the equilibrium is called the neutral equilibrium.

In the following figure,

1. The ball is put inside the spherical shell. Then this ball is said to be in a stable equilibrium position.

2. The ball is put upon a smooth sphere. Then this ball is said to be in an unstable position.

3. The ball is put on a smooth parallel floor. Then this ball is said to be in a neutral position.

What are static and dynamic equilibrium?

Static equilibrium is the physical condition of a system in which the constituents are at ease, and dynamic equilibrium is when the gadget remains in the condition of motion over the impact of some forces. The summation of the forces proceeding on them in the two cases is zero.

Static equilibrium is “any system where the addition of forces, and torque, on each object of the system occur to be zero. Generally, static equilibrium is the equilibrium of a system whose wedges are at rest”.

Dynamic equilibrium is a state of serenity and firmness. Dynamic refers to something having motion. The equilibrium is not stagnant. Hence, the dynamic equilibrium is also called chemical equilibrium.


By studying all the above facts, we conclude that when a system conducts a state of dynamic equilibrium, there is a grade of pressure between the reversing forces that is robust, deliberate, and constructed to attain the maximum results.

Megha BR

Hi, I am Megha B R, I have completed my Post-Graduation in Solid State Physics and pursuing B. Ed. I am a Physics enthusiast. As an Academic writer, my goal is to reach the readers in a simplified manner through my articles.

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