For each of the situations described below, the object considered is undergoing
ID: 1637466 • Letter: F
Question
For each of the situations described below, the object considered is undergoing some changes. Among the possible changes you should consider are: (Q) The object is absorbing or giving off heat. (T) The object's temperature is changing. (E) The object's thermal energy is changing. (W) The object is doing mechanical work or having work done on it. (C) The objects chemical energy is changing. For each of the situations described below, identify which of the four changes are taking place and mark as many of the letters Q T E W C (or none) as are appropriate. 1. A cylinder with a piston on top contains a compressed gas and is sitting on a thermal reservoir (a large iron block that maintains a constant temperature). After everything has come to thermal equilibrium, the piston is moved upward somewhat (very slowly). The object to be considered is the gas in the cylinder. Q T E W C 2. Consider the same cylinder as in part 1, but it is wrapped in styrofoam, a very good thermal insulator instead of sitting on a heat reservoir. The piston is pressed downward (again, very slowly), compressing the gas. The object to be considered is the gas in the cylinder. Q T E W C 3. A mixture of two moles of hydrogen gas and one mole of oxygen gas in a thermally insulated vessel of fixed volume is subjected to small spark (contributing negligible energy) and converts to water vapor. Q T E W C
Explanation / Answer
1.
After thermal equilibrium, the piston is moved upward, but very slowly. So temperature of the gas would remain constant. So thermal energy would remain constant. But the gas is expanding, so work is done and heat is exchanged.
So, the answer is, Q and W.
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2.
The cylinder is insulated. So no heat exhange takes place. But the compression ensures work and rise in temperature which also changes thermal energy.
So, the answer is, T, E and W.
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3.
Since the volume of vessel is fixed work done is zero. The vessel is insluated, so there is no heat exchange and the oxygen and hydrogen combine to form water vapour, so there is change in chemical energy as chemical bonds are broken and new bonds are formed. Also heat is released/gained during chemical reaction, so there would be change in temperature and thermal energy.
So, the answer is, T, E and C.
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This concludes the answers. Check the answer and let me know if it's correct. If you need any more clarification, modification or correction, feel free to ask.....
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