Thermodynamics Second Law in Hindi

Explanation: This question asks about the entropy of a perfectly ordered crystal when the temperature reaches absolute zero. Entropy represents the degree of disorder or randomness in a system. According to the third law of Thermodynamics, as temperature approaches absolute zero, Molecular motion nearly stops and the system becomes highly ordered. In a perfectly crystalline Solid, particles occupy fixed, well-defined positions, leaving no scope for randomness.

Entropy depends on the number of possible microscopic arrangements (microstates). In this case, only one arrangement is possible, meaning disorder is minimized. With no thermal energy available at absolute zero, particles cannot move or rearrange, so no additional disorder can arise. This leads the system to its lowest possible entropy state.

An easy analogy is a perfectly arranged puzzle where every piece fits exactly in only one way. There is no alternative arrangement, so randomness is absent.

In summary, entropy measures disorder, and a perfectly ordered crystal at absolute zero achieves the minimum possible entropy because there is only one arrangement and no particle motion.

Explanation: This question focuses on the thermodynamic condition required for a process to occur naturally without external assistance. Spontaneity is governed by the second law of Thermodynamics, which emphasizes the role of entropy. A process tends to occur if it results in an increase in the overall disorder of the universe, considering both the system and its surroundings.

It is important to evaluate the total entropy change rather than focusing on the system alone. Sometimes the system may become more ordered, but if the surroundings gain enough disorder, the overall effect still favors spontaneity. This combined entropy change determines whether the process proceeds naturally.

Another useful concept is Gibbs free energy, which incorporates entropy and enthalpy into a single parameter under constant temperature and pressure conditions. When the factors align to favor increased overall disorder, the process becomes feasible on its own.

For example, when perfume spreads in a room, molecules disperse from a concentrated region to a more random distribution, increasing disorder.

In summary, spontaneous processes are those that lead to an overall increase in disorder when both the system and surroundings are considered together.

Explanation: This question involves calculating work done during an isothermal expansion of a gas against a constant external pressure. In Thermodynamics, work is defined as the energy transferred when a system expands or contracts against an opposing pressure. For such processes, work depends on the change in volume and the external pressure applied.

During expansion, the gas pushes against the surroundings, increasing its volume. Since the process is isothermal, temperature remains constant, but that does not directly affect the work calculation in this case. The relevant expression for work under constant external pressure is given by multiplying pressure with the change in volume. Care must be taken with sign conventions, as expansion usually results in work being done by the system.

To compute this, the initial and final volumes are used to determine the volume change, which is then multiplied by the given pressure. Unit conversion is also essential, as L·bar must be converted into joules using the provided relation.

A simple analogy is pushing a piston outward—the farther it moves against resistance, the more work is done.

In summary, work during expansion depends on external pressure and volume change, requiring correct substitution and unit handling for accurate evaluation.

Explanation: This question examines what happens when two or more non-reacting gases are mixed. Entropy is a key concept here, representing the randomness or disorder of particles in a system. When gases mix, their molecules spread out and occupy a larger accessible volume, leading to greater randomness.

Before mixing, each gas is confined to its own region, limiting the number of possible arrangements. After mixing, molecules can move freely throughout the entire container, increasing the number of possible microstates. This increase in accessible configurations leads to higher entropy.

There is usually no chemical reaction or significant Heat change involved in ideal gas mixing, so the main effect observed is related to disorder. The process occurs naturally because systems tend to move toward states with higher probability and randomness.

An everyday example is opening two perfume bottles in a room—the scents gradually spread and mix, becoming more uniformly distributed.

In summary, mixing non-reacting gases leads to greater Molecular randomness and an increase in the number of possible arrangements, reflecting a rise in entropy.

Explanation: This question focuses on the thermodynamic criterion for spontaneity in terms of entropy. The second law of Thermodynamics states that any natural process must result in an overall increase in the entropy of the universe, which includes both the system and its surroundings.

Even if the entropy of the system decreases, the process can still be spontaneous if the surroundings experience a greater increase in entropy. Therefore, the total entropy change must be considered. This combined value determines whether the process proceeds without external intervention.

Mathematically, the total entropy change is the sum of the entropy change of the system and that of the surroundings. If this sum favors increased disorder, the process is thermodynamically feasible.

A common example is Heat transfer from a hot object to a cold one. The hot object loses entropy, but the cold object gains more, resulting in a NET increase.

In summary, spontaneity depends on the total entropy change of the system and surroundings, and natural processes occur when this combined effect leads to increased disorder.