Question

Explain spontaneous and non-spontaneous processes, giving two examples of each.

Answer 1

Hint:Spontaneous reactions are those chemical or biological reactions that take place without the influence of external factors. Non- Spontaneous reactions are those chemical reactions that require an energy input to proceed or that cannot take place without the influence of external factors.

Complete step by step answer:

Spontaneous reactions are those chemical or biological reactions that take place without the influence of external factors or without being driven by an outside force. Spontaneous changes are also known as natural processes .It basically does not require energy input as to proceed under particular conditions. In this case the total energy of the products is less than that of the reactants.
 These reactions also have negative enthalpy and it increases the entropy. These reactions tend to release the free energy from the system and thus make it more stable. These types of reactions occur rapidly and the change of Gibbs free energy $$\left(\mathrm{\Delta }G\right)$$ is a negative value, this can be explained as the release of free energy from the system corresponds to negative change in free energy but to a positive change for the surroundings.
 These reactions are also known as Exergonic reactions.
Examples for spontaneous reactions are:
Combustion Reactions
Ice melting in lukewarm water
Iron rusting
Salt dissolving in water
Non- Spontaneous reactions are those chemical reactions that require an energy input to proceed or that cannot take place without the influence of external factors. It requires energy input to proceed. In this case the total energy of the products is higher than that of the reactants.
 These reactions also have positive enthalpy and it decreases the entropy. These reactions tend to increase the total energy of the system. The total amount of energy is a loss as it takes more energy to start a reaction than what is gotten out of it. These types of reactions occur slowly and the change of Gibbs free energy $$\left(\mathrm{\Delta }G\right)$$ is a positive value.
These reactions are also known as Endergonic reactions.
Examples for non-spontaneous reactions are:
Diffusion of gas from low pressure to a high pressure.
Flow of heat from cold body to a hot body.
Combination of nitric oxide and oxygen to form nitrogen dioxide

$\mathrm{\Delta }G=\mathrm{\Delta }H-T\mathrm{\Delta }S$
Where, $\mathrm{\Delta }G$ is Gibbs free energy $\mathrm{\Delta }H$ is the change in enthalpy and $\mathrm{\Delta }S$ is the change in entropy.

Note:
Gibbs free energy $$\left(\mathrm{\Delta }G\right)$$ is the free energy of a system is the sum of its enthalpy $\left(H\right)$ plus the product of the temperature in Kelvin and the entropy $\left(S\right)$ of the system. Enthalpy $\left(H\right)$ is a property of a thermodynamic system. It is defined as the sum of a system's internal energy and the product of its pressure and volume. Entropy $\left(S\right)$ can be defined as the property of a system which measures the degree of disorder or randomness in the system.