Heat will naturally move from hot to cold without any external input because the overall system is trying to reach an even temperature. You can understand entropy as either reaching equilibrium, or as increasing disorder of a system.Īn example of a spontaneous process is heat moving from a hot to a cold body. According to the second law of thermodynamics, in a spontaneous process, entropy must increase.
∆S universe = ∆S system + ∆S surroundings Spontaneous ProcessesĪ spontaneous process is one that occurs without any input. Processes can allow entropy of a system to decrease, but in that case, entropy of the surroundings will increase.
All systems are always trying to reach equilibrium, and increase their Gibbs Free Energy. Until finally, when everything is one temperature, you cannot get any work out of it, even though all the energy is still there. It is impossible to construct an engine which will produce no effect other than extracting heat from a hot reservoir and converting it into an equivalent amount of work. This is because, achieving maximum entropy means that a system is at equilibrium. Now, according to the Second Law of Thermodynamics, there is always a tendency for the hot areas to cool off and the cool areas to warm upso that less and less work can be obtained out of it. According to Kelvin Plank statement, second law of thermodynamics is stated as. According to the second law, entropy of a spontaneous process must increase, and the the entropy of the universe must always increase. The second of the law of thermodynamics deals with entropy and, to an extent, limits the first law. If the system does work on its surroundings then work is negative. If the surroundings does work on the system, then work is positive. This means that heat lost by the system is equal in magnitude to the heat gained by the surroundings (exothermic reaction). If heat flows out of the system, Q is negative. This means that heat is gained by the system, and the same magnitude of heat is lost by the surroundings ( endothermic reaction). If heat flows into the system, Q is positive. So, heat and work are are two processes which can change the internal energy of a system.
Another way of restating the first law, is to say that the change in energy is equal to the heat flow across the system (Q) plus the work done on the system or by the system (W).
However, it is important to note that energy takes different forms. In other words, total energy of the universe must remain constant. The first law is the conservation of energy, summarized by: energy cannot be created or destroyed. In other words, refers to both the system and the surroundings. Anything inside the boundary is called the “system,” and anything outside the boundary is called the “surroundings.” Once the boundary diagram is drawn, the movement and transfer of energy can be characterized by the flow across system boundaries. Thermodynamics becomes much easier when a clear boundary is drawn.