A steady state is a state where the rate of formation of a species equals the rate of its decomposition in a consecutive reaction. On the other hand, chemical equilibrium is the condition of a reversible reaction taking place where the rate of forward reaction is equal to the rate of backward reaction.

A system having steady state changes with time but the net rate remains constant. This is generally used in consecutive reactions where the rate of overall reaction is constant i.e. the rate of formation of a product is equal to the rate of its decomposition.

For example

A → B → C

The rate of the first reaction equals the rate of the second reaction. i.e. Rate of formation of B equals the rate of its decomposition.

## Chemical Equilibrium

Chemical equilibrium is a state achieved by the system when the rates of forward and backward reactions are equal. This equilibrium refers to reversible reactions where both reactants and products are present all the time.

For example

A + X  ⇋  B + Y

 Steady State Equilibrium The term is used for consecutive changes over time. When they reach a certain condition where the concentration of a substance (intermediate), is no longer to change over time It is used for reversible reactions when they reach a certain condition where concentration is no longer to change over time The system is not at equilibrium which states that the entropy is increasing with time A → B → C The entropy remains constant in equilibrium A ⇋ B If the rate for the first reaction is k1 and for the second one is k2k1 = – k2 The rate of formation B is equal to the rate of decomposition of B. k1 = k2 Steady-state is a condition that implies an open system An equilibrium is established in a closed system There may be a transfer of heat due to an open system In equilibrium, no net heat transfer due to a closed system In open systems, equilibrium can not be achieved but the steady-state can be achieved easily when incoming or outgoing heat or mass are equal A → B → C In equilibrium, A can be changed into B and B can be changed into A, but net concentration remains constant A ⇋ B It is established in kinetically controlled processes It is achieved in thermodynamically controlled processes

A reactant A converting into an intermediate B and at the same time B converting into a product C is a consecutive reaction. The rate of change of reactants to products i.e. from A to B is k1 and from B to C is k2. The system is said to be in a steady state if the rate of formation of B is equal to the rate of decomposition of B.  ## Explanation of Chemical Equilibrium

There are two reactants A and B. Before establishing the equilibrium between them, the concentrations of both A and B reactants are in the initial states.

After a certain period of time, when the reaction starts proceeding and reactants are converted to products, the concentration of reactants becomes constant. That is, the rate of forward reaction becomes equal to the backward reaction.  Related topics

## Thermodynamic equilibrium

“Thermo” means “heat” while “dynamic” means “in motion” or “in flow”. Heat is defined as the transferable amount of energy that travels from one body to another due to the differences in temperature levels. Heat is a path function. It flows from high temperature towards low temperature.

For example

If we place a glass of water in an empty room. We can observe the difference in the temperature of the glass and the room. The temperature of the glass is 50°C and the temperature of the room is about 20°C. After some time, the temperature of both glass and room becomes the same. The heat from the glass transfers to the surroundings, i.e. to the room. The net change of heat is zero, once thermodynamic equilibrium is achieved. Consider a system in which a beaker half-filled with water and the thermostat of the hot plate is set at 50°C. If we observe the change in the temperature of water present in a beaker, the temperature of the water reaches 47°C and stops increasing. The reason is that the beaker is an open system. The heat travels from the hot plate to the beaker and from the beaker to the surrounding. Therefore, overall heat change in the two systems becomes equal. This condition is called the steady-state condition in thermodynamics. ## Concepts Berg

How is equilibrium different from a steady-state system?

Steady-state and equilibrium are different entities. Chemical equilibrium is the condition in which the rate of forward reaction becomes equal to the rate of the reverse reaction. The concentration of reactants and products becomes constant. An example is the production of ammonia by the Haber process.

N2 + 3H⇌  2NH3

Whereas, a steady state is the condition in which change is occurring constantly over the period and some of the properties like entropy are increased with time contrary to chemical equilibrium.

For example

A beaker is placed over a hotplate and its temperature is maintained at 60oC. It is the perfect example of a steady-state condition. Here heat is flowing from the source to the system and then from the system to the surrounding where entropy increases with time, keeping the temperature constant.

Source → System → Surrounding

What is the difference between thermal equilibrium and steady state condition?

Thermal equilibrium is the condition where the temperature of the system becomes equal to the surroundings hence, heat transfer to surroundings becomes zero.

{Source ⇋  System}  (closed system)

While in a steady state, heat flows from the source to the system and then to the surrounding. Here the temperature is constant and entropy is increasing with time.

Source → System → Surrounding  (open system)

What is meant by equilibrium state in semiconductors?

A semiconductor is a device that is made by dopping P-type and N-type materials. P-type materials are formed by dopping group 4 elements e.g Silicon (Si), Germanium (Ge) with group 3 elements e.g Aluminium (Al). N-type materials are formed by doping Si, Ge, etc with group 5 elements e.g Nitrogen (N). P-type materials have excess holes while N-type materials have excess electrons, the electrons-hole movement occurs at the P-N junction. When this movement becomes constant, the system is said to be in equilibrium.

Why are chemical plants operated at a steady state but not at equilibrium?

Chemical plants are operated on the steady-state principle because there is a constant flow of heat energy from the source to the system as well as from the system to the surrounding. It remains constant over a period of time.

Source → System → Surrounding

while at equilibrium a completely closed system is required, meaning no loss of mass and heat during the reaction. This is an ideal case, which is not feasible.

How do you find the final equilibrium temperature when a hot iron mass is placed in water?

When a hot iron bar is placed in the water container, it starts dissipating its heat into the surrounding water. The temperature of water increases until both water and iron bar have the same temperatures. However, the water container loses its heat to the surroundings as well. This means the water container is also establishing equilibrium with the surrounding.

Here the final equilibrium temperature should be noted when equilibrium is established between iron bar, water, and surrounding.

What is dynamic equilibrium?

When reactants are converted into products and products into reactants simultaneously, the concentrations remain constant. The equilibrium is said to be dynamic.

What is the non-equilibrium steady state?

Non-equilibrium steady state is a condition in which a steady state has an abrupt change in mass and heat over a specific period of time. And that change can be noted easily. The existence of a non-equilibrium steady state proves the difference between steady-state and chemical equilibrium.

Is a system at equilibrium always at a steady-state?

No, a system at equilibrium is not always at a steady state. By definition, a system in a steady state has a certain fixed value of heat but mass or any other property could be changed in the system while the system is at equilibrium in a closed system where mass, heat, or entropy all remain constant.

Why does a cell maintain a steady state?

A cell has to maintain a steady-state condition in order to survive because it regulates water and glucose with its surroundings. If by any chance a sudden change occurs, which may damage the cell, is avoided by maintaining a steady-state with surroundings.

The constant flow of heat from the source and into the system and to the surroundings is called steady-state flow.

Source → System → Surrounding

Steady-state is the condition in which change is occurring constantly in a system over a period of time.

What is the equilibrium constant Kc?

The equilibrium constant is the ratio of the concentrations of products and reactants in a chemical reaction.

For example

2SO2 + O2  ⇌  2SO3

Kc = [SO3]2   /   [SO2]2 . [O2]

Write the equilibrium constant expression for the given reaction? Give units

2NOCl 2NO + Cl2

Kc = [NO]2 . [Cl2]  /  [NOCl]2

Units

Kc = [ mol/dm3]2 . [ mol/dm3]  /  [mol/dm3]   mol/dm3

State Le Chetelier’s principle? Explain the change in equilibrium position with a change in temperature?

Le Chetelier’s principle:

“If the system is disturbed at equilibrium, it will react in such a way as to minimize the effect of that change.”

For example

If the amount of reactant is increased at equilibrium, the reaction will move in the forward direction trying to re-achieve the equilibrium. Kc remains constant for this reaction.

In exothermic reactions, heat is released (as a product of the reaction). So, by the rule, the reaction will move backward when heat is added into the system.

While in endothermic reactions, upon heating, the reaction will go forward and vice versa.

References

• Fundamentals of Equilibrium and Steady-State Thermodynamics by N.W Tschoegel