Q1.Zeroth Law of Thermodynamics: The zeroth law is also called law of equilibrium. It states that if a body A is in thermal equilibrium with a body B and in turn body B is in thermal equilibrium with body C then body A and C are also in thermal equilibrium with each other. First Law of Thermodynamics: The first law of thermodynamics is also called the law of conservation of energy and it states that the energy is always conserved; it can neither be created nor destroyed though energy can be converted from one form into another. ∆E System = 0Second Law of Thermodynamics: The second law of thermodynamics is also called the law of entropy.
This law predicts that the degree of randomness (entropy) of any isolated system always increases with time. There are several statements which explain second law of thermodynamics. ∆S System ≥ 0Kelvin-Planck statement: It is impossible for any heat engine to produce net work in a complete cycle if it exchanges heat only with bodies at a single fixed temperature. Thus to produce the work the cycle should exchange heat with two reservoirs which are a different temperatures.
The reservoir at high temperature is the source and other one at low temperature reservoir is the sink. Clausius statement: It is impossible to construct a device which, operating in a cycle, will produce no effect other than the transfer of heat from a colder to a hotter body. Thus in order to transfer heat from low temperature reservoir to high temperature reservoir, external work must be done on the cycle. Third law of thermodynamics: It is a statistical law of nature regarding entropy and the impossibility of reaching absolute zero of temperature.
It states that the entropy of a substance approaches zero as its temperature approaches absolute zero. Q2)Entropy can be defined as degree of randomness. It is an index of unavailability or degradation of energy. Heat always flows from hot to cold body and thus becomes degraded or less available. Thus unavailability of energy is measured by entropy. We are usually interested in changes in entropy. Entropy is a property of system. Entropy changes always occur accompany actual heat transfer but it can also change without any heat transfer.
For a reversible transfer of heat, change in entropy is given by∆S = ∑ ∂Q/T For a reversible adiabatic process, change in entropy is zero thus called isentropic process. When ice melts into water the degree of randomness of the molecule increases and hence the entropy of the system increases. Moreover it is evident from the fact that no process between two equilibrium states is possible if it would result in decease in the total entropy of a system and its surroundings.
Water in vapour form has molecules moving freely. Thus it has very high entropy. But as vapour cools, it becomes liquid. The liquid water molecules still move around, but not that freely. They already lost some entropy. Further when water cools, it becomes ice. Ice molecules can no longer move freely, but can only vibrate within the ice crystals. The entropy is now very low.