Criteria for Equilibrium and Spontaneity

What is Equilibrium?

An object is said to be in a state of equilibrium if all the opposing forces or influences applied to it are balanced. 

• • In physics, equilibrium occurs when neither the internal energy nor the state of motion of an object changes with time.

• Mathematically, equilibrium can be denoted as Fnet = ma = 0, where Fnet is the net force. 

• There are three types of equilibrium. These are stable, unstable, and neutral equilibrium. 

• When an object is in a state of equilibrium, the object doesn’t experience any acceleration, and the net force and net torque applied to the object is zero. 

• An object will be considered in a state of equilibrium if it is in motion and continues to move in the same direction and pace. 

• An object is in a state of dynamic equilibrium if there is no observable change in the system when the reverse and forward processes occur at the same rate. Dynamic equilibrium occurs when the rate of loss equals the rate of gain. 
• A chemical reaction in a state of dynamic equilibrium will stop when any one of the reactants has run out. 
• When a system and its surrounding is in a state of thermal equilibrium, then the temperature of the system and its surroundings are the same. 

Static equilibrium meaning 

A system whose parts are in a state of rest is in a state of static equilibrium. If an object is in a state of static equilibrium, its net force through the system is zero, and all its components are at rest. 

• An object is said to be in a state of static equilibrium if that object is not in motion in relation to the relative and if all of the forces acting on the object are balanced. 

• An object will also be in a state of static equilibrium if its linear momentum is zero, ergo the object is not moving, and when the sum of its torque from every direction is zero. 

Spontaneity 

Spontaneity or spontaneous reaction refers to a change that does not require the assistance of an external agency. We cannot reverse the direction of the spontaneous reaction or process on its own. Therefore, a spontaneous reaction or process is considered an irreversible process that is reversible with the help of an external agency. 

In the case of exothermic reactions, a chemical reaction will qualify as a spontaneous reaction if a decrease in energy has taken place. While a decrease in enthalpy is considered a contributory factor for spontaneity, it does not apply to all cases. 

• A criterion for spontaneity in an isolated system is the tendency for the energy within the system to become more chaotic or disordered. Higher levels of disorder and chaos contribute to higher entropy levels in an isolated system.

• The total entropy change determines the spontaneity process. 

• Either decreased enthalpy or increased entropy cannot determine the direction of spontaneous change in the system. 

• If the △TS outweighs the △H, and the reaction has both positive enthalpy change and positive entropy change, the process is considered spontaneous. 

Gibbs energy or Gibbs function 

Gibbs energy is a thermodynamic function. Gibbs function is denoted as G.

• Gibb free energy = G = H – TS. Where G is Gibbs free energy, H is enthalpy, S is the entropy, and T refers to the temperature in Kelvin, K.
• The SI unit of G is k Jmol
• Gibbs energy equation is Gibbs energy change = enthalpy change – temperature entropy change or △G = △H – △TS. This equation is one of the most important equations in chemistry. That’s because it helps design experiments in the lab as scientists can ascertain how a reaction will proceed at a particular temperature. 
• If the change in Gibbs energy is negative, then the process is spontaneous; however, if the change is positive, then the process is considered non-spontaneous. 
• The system is in equilibrium if the change in Gibbs energy equals zero. In this case, the concentration of products and reactants remains constant. 
• Change in Gibbs energy is negative either when the entropy of the system increases and the process is exothermic or when the entropy of the system decreases, and the process is endothermic. 

Example-Calculate △G for ice melting at -10 ° C. 

Solution- T = -10 ° C + 273 = 263 K 

△G = △H – △TS 

= 6.01 k Jmol – (263 K) 0.022 k J mol 

= 6.01 k Jmol – 5.79 k Jmol

= 0.022 k J mol 

Therefore, at -10 ° C, △G = 0.022 k J mol 

Conclusion 

With this, we conclude our article on the criteria for equilibrium and spontaneity. In this article, we looked at the different conditions required in an object to achieve the state of equilibrium. Additionally, we have discussed static and dynamic equilibrium, along with spontaneity and how spontaneous reactions occur without the help of external energy.