【Daily Question】Theoretical Foundation 2020.05.12

The last edit to this post was made by h20090630 on 2020-5-12 at 09:38. B. In the process from A to B, the temperature of the gas remains constant while the pressure increases; using Boyle’s law, it is possible to determine how the volume of the gas changes； When the gas volume increases, the gas does work on the outside; when the volume decreases, the outside does work on the gas ； Temperature is an indicator of the average kinetic energy of molecules; the internal energy of an ideal gas is determined by its temperature. As can be seen from the graph, during the process from A to B, the temperature of the gas remains constant while the pressure increases. According to Boyle’s law, the volume of the gas decreases, so VB < VA ； A. The mass of the gas remains unchanged while its volume decreases; according to the density formula, the density of the gas increases ； B. The volume of the gas decreases, and work is done on the gas by the external environment; therefore, B is correct ； C. When the gas temperature remains constant, its internal energy also remains constant; thus △U = 0. Work is done on the gas by the external environment, so W > 0. According to the first law of thermodynamics, △U = Q + W, it follows that Q < 0 – the gas must release heat. Therefore, C is incorrect ； D. Since the gas temperature remains constant, the average molecular kinetic energy also remains constant; therefore, D is incorrect ； Therefore, the answers are AB. Comment: Based on the graph, applying Boyle’s law to determine how the volume of the gas changes is the prerequisite and key to solving the problem correctly; to determine whether the gas absorbs or releases heat, it is necessary to take into account the application of the first law of thermodynamics