SAT Physics: Laws of Thermodynamics Laws of Thermodynamics This lesson will be focused on the four laws which govern the world of Thermodynamics. These are : ● Zeroth Law of Thermodynamics ● First Law of Thermodynamics ● Second Law of Thermodynamics We will focus very superficially on the Zeroth law but divert more attention towards the first and second law, simply because they are more likely to turn up in the exam. Zeroth Law of Thermodynamics The Zeroth Law is basically tautology, which is probably why no one opted to put their name as the founder of this law. Anyway, the Zeroth Law of Thermodynamics states that, “ If Object A and B are in thermal equilibrium with Object C, then Objects A and B are in thermal equilibrium with each other ” Quite self-explanatory. To sum it up, this law basically states that when two objects come in contact, heat energy will flow from the warmer object to the cooler object until a state of thermal equilibrium is achieved and neither side is colder or warmer than the other. First Law of Thermodynamics The first law of thermodynamics is basically a reiteration of the Conservation of Energy (energy can neither be created nor destroyed), but this time applied to an actual system. If the amount of energy ΔQ is given to a system, then either the internal energy of the system ΔU increases or the ΔW, Work done increases. Whilst one must increase, it is perfectly acceptable for both of them to increase. We can express the first law mathematically, with the equation: ΔQ=ΔU+ΔW When ΔQ is positive, heat energy is going into the system. Alternatively, if it is negative, heat energy is going out of the system. Additionally,if ΔU is positive, the internal energy of the system is increasing. Simultaneously, as you increase the internal energy of the system, you also increase its temperature. Similarly, if ΔU is negative, the internal energy of the system is decreasing. Lastly, if ΔW is positive, then the system is doing work on the surroundings and the gas is expanding. Conversely, if ΔW is negative, then the surroundings are doing work on the gas, and if you do work on the gas, you are basically contracting the gas. Second Law of Thermodynamics
To fully grasp the concepts of the Second Law of Thermodynamics, we must first get a solid understanding about this idea of Entropy. Look at the diagram below This looks quite ordered right? This is a diagram of a liquid and the particle configuration. We can see that the system here is quite ordered, as in the number of possible arrangments in which you can arrange the particles are not too high, as most of the particles do not have a lot of freedom of movement.