Why is equilibrium a dynamic condition

The side where there is more gas is the side in which the equilibrium will shift to if the pressure is decreased, because more can fit now. Vice versa as well. There are many factors that shift equilibrium Kc so we must always be wary of these factors before we jump to a conclusion about what the equilibrium is, because it is very dynamic!

Good question Now, by definition, the chemical condition of equilibrium is defined when the forward and reverse rates are equal:. However, a chemist or engineer can certainly manipulate the equilibrium. For instance, if we remove somehow the products of the reaction, C and D , the equilibrium will have to re-establish itself, and it does this by moving to the right as written to satisfy the equilibrium equation, and to re-establish equilibrium concentrations of C and D.

On the other hand, if we pump more reactant into the equilibrium, the equilibrium will move in a forward direction to cope with increased [A] and [B]. There should be many answers here that deal with equilibria. Eventually, however, the amount of the product HI increases, and it will begin producing H 2 and I 2.

Thus the rate of the reverse reaction starts out slowly there is no HI present , but will speed up as the concentration of HI increases.

Eventually both rates will level off not always to the same level as shown by this example, however :. Chemists have found that there is a mathematical relationship that exists between the concentration of the reactants and products, once equilibrium has been reached, that is independent of the initial concentration of the participants. For any general reaction,. This mathematical relationship exists for all equilibrium systems, and produces a constant ratio called the equilibrium constant, K eq.

This relationship will be very important to us for the next few units, so it is important that you understand how to set this relationship up and what it tells us about an equilibrium system.

The products of the reaction C and D are placed in the numerator, and their concentrations are raised to the power of the coefficients from the balanced equation. The reactants A and B are placed in the denominator, with their concentrations raised to the power of their coefficients.

Using the example we examined in our last section, equilibrium concentrations for each substance were measured at equilibrium and found to be:.

The value of K eq , which has no units, is a constant for any particular reaction, and its value does not change unless the temperature of the system is changed. It does not depend on the initial concentrations used to reach the point of equilibrium.

For example, the following data were obtained for equilibrium concentrations of H 2 , I 2 and HI, and the value of K eq was calculated for each trial:. Aside from accounting for slight experimental variation between trials, the value for K eq is the same despite differences in equilibrium concentrations for the individual participants.

K eq relates the concentrations of products to reactants at equilibrium. For gases, concentration is often measured as partial pressure. The concentrations of both aqueous solutions and gases change during the progress of a reaction.

For reactions involving a solid or a liquid, while the amounts of the solid or liquid will change during a reaction, their concentrations much like their densities will not change during the reaction. Instead, their values will remain constant. Because they are constant, their values are not included in the equilibrium constant expression. For example, consider the reaction showing the formation of solid calcium carbonate from solid calcium oxide and carbon dioxide gas:.

But we remove those participants whose state is either a solid or a liquid, which leaves us with the following equilibrium constant expression:. This page was constructed from content via the following contributor s and edited topically or extensively by the LibreTexts development team to meet platform style, presentation, and quality:. Learning Objectives Describe the three possibilities that exist when reactants come together. The three reaction systems 1, 2, and 3 depicted in the accompanying illustration can all be described by the equation:.

Each set of panels shows the changing composition of one of the three reaction mixtures as a function of time. Which system took the longest to reach chemical equilibrium? Compare the concentrations of A and B at different times. The system whose composition takes the longest to stabilize took the longest to reach chemical equilibrium.

Thus system 2 took the longest to reach chemical equilibrium. The sets of panels represent the compositions of three reaction mixtures as a function of time. Dynamic equilibrium doesn't just occur in chemistry labs though; you've witnessed an dynamic equilibrium example every time you've had a soda. The two phases of carbon dioxide are in dynamic equilibrium inside the sealed soda bottle since the gaseous carbon dioxide is dissolving into the liquid form at the same rate that the liquid form of carbon dioxide is being converted back to its gaseous form.

Changing the temperature, pressure, or concentration of a reaction can shift the equilibrium of an equation and knock it out of dynamic equilibrium. This is why, if you open a soda can and leave it out for a long time, eventually it'll become "flat" and there will be no more bubbles. This is because the soda can is no longer a closed system and the carbon dioxide can interact with the atmosphere.

This moves it out of dynamic equilibrium and releases the gaseous form of carbon dioxide until there are no more bubbles. For example, say that you prepare a solution that is saturated with an aqueous solution of NaCl.

If you then add solid crystals of NaCl, the NaCl will be simultaneously dissolving and recrystallizing within the solution. Nitrogen dioxide NO 2 reacts with carbon monoxide CO to form nitrogen oxide NO and carbon dioxide C O 2 , and, in the reverse reaction, nitrogen oxide and carbon dioxide react to form nitrogen dioxide and carbon monoxide. This is an equation for the formation of rust.

If you observe reactions at dynamic equilibrium and reactions at static equilibrium, neither will have visible changes occurring, and it'll look like nothing is happening.

However, reactions at static equilibrium are actually very different from those at dynamic equilibrium. Static equilibrium also known as mechanical equilibrium is when the reaction has stopped and there is no movement at all between the reactants and products. The reaction is complete and the forward and reverse reaction rates are both 0. While reactions at dynamic equilibrium are reversible can proceed in either direction , those at static equilibrium are irreversible and can only proceed in one direction.

However, both dynamic equilibrium and static equilibrium are examples of systems at steady state, in which the net force action on the systems is zero. When a reaction is at dynamic equilibrium, the reaction will have a specific rate constant, known as the equilibrium constant, or K eq.