The first law of thermodynamics describe how heat and work can change the internal energy of a system for an adial gas. In this lab, students were able to prove how it works and also how the change in the total mechanical energy of the system will affect the work and the amount of heat, when it existe, that is transferred to or from the system.
In this picture students were asked to predict on three different situations, what would happen when the candle was placed inside a jar, a small one and big one. The prediction, the upper left side, was that the candle's flame would dime faster and then go out. The reason is because no air was circulating inside the jar, and since oxygen, one of the most important factors to keep the flame 'vivid', called also fuel, was cut, the flame went out.
In the second prediction, the down left side, a tube had been added. This time the flame kept the flame more brightly since it had air that was circulating between the jar and the tube. The closer the tube was to the candle, more dimed the flame was. And when the tube was far from the candle, more agitated the flame was. This happens because the space between the candle and the tube had a bigger column of air.
In the third prediction, the candle was placed inside of a big bottle of glass and drooped from a height of 6 inches. The result was for instance the candle's flame was burned brightly since it, presumedly, the column of air was compressed and was burn faster as the big bottle was dropped; and at the end started to dime because the oxygen had almost been consumed by the flame.
In the first picture, the students were trying to see if the what happens when a mass in placed on the top of cylinder. In this case, the mass will do work on the gas ( negative work, -W) to compress it. As the gas is compressed, the temperature increases since the molecules will not have the same space to move around and because they will be hitting each other with more frequency; the volume decreases, causing what was explained before, the decreasing in space between the molecules and the walls of the cylinder.
The second picture shows a mechanism that can be used to actually see how pressure and temperature can increase, while the volume of the gas is decreased. Starting as an ideal mechanism, means that no heat is lost, and the internal energy is conserved, the gas is slowly compressed, the gage will start reading the increasing pressure inside the cylinder as well as the digital thermometer.
This photo represents the various types of processors that can be found. the first one is A (Isobaric, iso - unique, baric - pressure), means that the phase changes that a gas suffer will be at constant pressure, while the volume will keep increasing. The second one is B (Isochoric, choric - volume), means that the changes that a gas suffer, from one phase to another, will be at constant volume, while the pressure will keep increasing. The third and fourth graph are very similar, but one is faster than the other; In C (Adiabatic) the phase change, for example from point 'a' to 'b', is so fast that the only thing that is kept constant is the pressure and the volume will decrease at same rate that the pressure increases. On D (Isothermal, thermal - temperature) since is a slow process, the gas will 'have time' to increase its temperature as the pressure as well. Likewise, the volume here will decrease because the space between the molecules and the walls of the recipient will get smaller.
The first picture explains how a rubber band when heated will contract and lift an object, move it from one place to another, either a higher one or one that is besides of the first one, drooped when is cooled, since it will extend, and then repeat the same process all over again. However, this process is to slow and the rubber band would not last longer. This happens because until a certain point the rubber ban will keep its elastic properties, each are the ones that even been heated and cooled, it will 'never' change its initial properties. After a long using of this process, the rubber band will pass to a plastic phase, where the initial conditions are no longer present. It means that every time that it is heated, to return to the nearest original form will take more time, and will never be the same.
P.S.: Although in the elastic process its assume that returns to its original, this happens to the ideals processes. The true is that once the rubber band, and to any material, is heated, some of its original properties are lost, and it does not return completely to its original position. Yet, because it is so small the lost, it is considered that the mass retain its properties when it gains and losses heat.
This picture above, is an illustration of how a Carnot Cycle works. Heat is added to the engine through the hot reservoir, and at the same time the gas starts to do work because it gain the temperature that the hot reservoir hat. At this point no heat is lost. In this case the process in which the increasing of volume is done isobarically (the gas does work, +W), at constant pressure, from 1 to 2. Next, from 2 to 3, the gas does work on its surroundings, which means that heat is been delivery by the system to its surroundings. To keep the process reversible, the same amount of heat the gas losses must be the same that the surroundings will gain. And this process is done isochorically, at constant volume. From 3 to 4, the gas suffers again an isobaric process, but this time the gas is been compressed. It means that the cylinder is doing work on the gas (-W), reducing the volume of it by having the same pressure. Then, from 4 to 1, the gas is heated again, and work is done on it isobarically.
The link below the picture can illustrate the Carnot Cycle. Here, heat is added to a gas inside a cylinder, and it starts to move from one side to another. It is assumed that no heat is lost, so the total internal energy is zero, and the total heat that is been added to the cylinder is converted into work.
In this three pictures, the students were asked to analyze the Carnot Engine. French engineer Sadi Carnot developed an idealized engine that was able to explain the first law of the thermodynamics, where the idea was to reach the maximum efficiency that could be reached. This means that the engine would have a reversible process, where every heat added to the engine, could be recovered to be reused. This method is now known as the Carnot Cycle. Students were able to calculate the quantities asked, such as heat hot and cold, it means the heat added (hot) and losted (cold), work, and work net, that is the difference between the heat hod and heat cold. They also calculated the efficiency of it as shown. From this, it can be seen that the internal energy does not conserve because the engine was not 100 percent efficient. Some heat was lost during each process, and converted in to heat that could not be recovered.
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