Gay Lussac S Law Gay Lussac S Law The expression Gay-Lussac's law is used for each of the two relationships named after the French chemist Joseph Louis Gay-Lussac and which concern the properties of gases, though it is more usually applied to his law of combining volumes, the first listed here. One law relates to volumes before and after a chemical reaction while the other concerns the pressure and temperature relationship for a sample of gas. Experiment on Gay Lussac's law :- The molecules in a gas are in constant random motion. In their frantic movements, the molecules collide with each other and with the walls of their container. The container is fitted with a piston and a pressure gauge to measure the change in pressure due to collisions of gas molecules against the container. If we heat the gas, then the energy of the molecules increases. This means, on an average, they increase their speeds. They hit the walls of the container harder, which results in the piston moving outwards, so, the volume of gas increases. However, when the gas finishes expanding and the piston stops moving, equilibrium is established again. If we assume the outside pressure remains constant, then the pressure inside the gas at equilibrium must be the same at the end of heating as it was at the start.
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The expansion of gases was investigated by J.A.C Charles in 1787, but it was Gay in 1801, who first published a systematic set of results, which formed the basis of the following law. Gay – Lussac’s law explanation Let us assume that a gas like nitrogen is kept in a container with a constant volume and a number of moles. The pressure is also maintained at 2 atmospheres along with a temperature of 35 degree Celsius. When we try to increase the temperature of the gas, the molecules of the gas start colliding with each other, since with the increase in temperature, the kinetic energy of the molecules also increases. Once the kinetic energy increases, the molecules start moving faster and once they collide, they move away from each other due to impact of collision and this results in decrease of pressure. So, with the increase in temperature, molecules move faster and the pressure decreases as they move away from each other. Gay Lussac’s Law of Combining Volumes :Gay Lussac gave a new law, almost in accordance with the Boyle’s law and Charles law. The statement of his law was When gases combine together they do so in volumes, i.e., in a simple whole number ratio to each other and to that of the product, if it is a gas. In the case of Gay Lussac’s law, it is assumed that the gas volume is measured at the same temperature and pressure. Gay Lussac was also correct about the results of his experiments leading to the time when it became possible to predict not just what would be made in a chemical reaction, but how much would be made.
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Dalton was not quite convinced with the Gay Lussac’s law. According to him, gases do not unite in equal or exact measures in one instance; when they appear to do so, it is owing to the inaccuracy of our experiments. But later, a connection was seen between Gay Lussac’s work on volumes of gases and Dalton’s idea that all chemicals were built from individual atoms. Question: A sealed Iron container containing 4 meter cube of the nitrogen gas at 0.99 atm and 25 degree Celsius is thrown into fire where the temperature is 1100 degree Celsius. What is the new pressure of the gas in the container? Assume constant volume and ideal behavior. Solution: Initial conditions Pressure = P1 = 0.99 atm Temperature = T1 = 25oC + 273 K = 298 K Final conditions Pressure P2 = ? Temperature T2 = 1100oC + 273 = 1373K P1 / T1 = P2 / T2 We need to find P2. So, P2 = P1 / T1 X T2 = 0.99 atm / 298 K x 1373 K = 4.56 atmospheres.
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