# Static and Dynamic Equilibrium explained with their differences

### What is static and dynamic equilibrium?

In English language, dynamic means 'changing' while static means 'no movement'.

In chemistry, static equilibrium (also called mechanical equilibrium) involves an interacting system or reaction whereby there isn't any movement of molecules between the reactants and products. Such reaction is said to be complete since the rate of reaction becomes zero.

An instance of static equilibrium is seen when diamond (an allotrope of carbon) is converted to graphite, another allotrope of carbon.

You can read on the concept of allotropes in Dalton's atomic theory here.

Graphite is a more stable allotrope of carbon, making it almost impossible to become converted into diamond. However, diamond may still be converted into graphite but at a very high activation energy. To this end, it must be heated above 2000°C before it show signs of convertion into graphite. This therefore implies that without an application of temperature (heat), the conversion process of diamond into graphite will likely take billions of years at room temperature. See the equation below:

C(s) (diamond) -> C(s) (graphite)

From the above equation, we can safely say that both allotropes of carbon (diamond and graphite) exists in static equilibrium since their reaction rate is effectively zero at room temperature.

Static equilibrium is typically unidirectional in nature. In fact, when a unidirectional reaction uses all its limited reactants, static equilibrium is said to be reached because the backward reaction cannot proceed, thus bringing the reaction rate to zero. We can therefore conclude that such reaction is ended at this point.

You can read on compounds and their characteristics here.

In physics, when the forces acting on an object nullifies each other, thus bringing about a constancy of content (that is, content remains the same in composition and without any form of movement), then static equilibrium is said to be reached.

The image shows a system in static equilibrium: • W = Weight
• r = Distance from the pivot point to where the force was applied (weight)
• F = Magnitude of the force

You can read on Newton's laws of motion here.

Dynamic equilibrium (also called chemical equilibrium) is defined as a state whereby the rate of forward reaction equals that of the backward reaction even though the movement of substances still occurs between both (reactants and products). In addition, the concentration of the reactants and products remains constant with time while the system shows no further change in properties.

You can read on Le Chatelier's principle here.

Dynamic equilibrium will always occur in a reversible chemical reaction (denoted by ⇌).

The images below shows a summary of how a system in dynamic equilibrium (chemical equilibrium) works  However, since dynamic equilibrium is reversible in nature, it will therefore occur only in closed systems while using chemical reactions as a point of reference; unlike static equilibrium which may take place in both open and closed systems.

### Differences between static and dynamic equilibrium

The table below summarizes the differences between static and dynamic equilibrium:

#### Dynamic Equilibrium

The reaction ends. There isn't any further reaction in the system Chemical reaction between the reactants and products are still ongoing at equal rates
It can occur in both open and closed systems It occurs only in closed systems
The reaction is irreversible in static equilibrium The reaction is always reversible in nature
The rate of reaction is zero, thus such reactions are completed The forward and backward reaction rates are always equal
Static equilibrium is always explained in mechanical processes. For this reason, it's also called mechanical equilibrium Dynamic equilibrium is always explained in chemical processes. For this reason, it's also called chemical equilibrium

You can read on the differences between physical and chemical change here. 