2.26. Demonstrate that the interval energy U of the air in a room is independent of temperature provided the outside pressure p is constant. Calculate U, if p is equal to the normal atmospheric pressure and the room's volume is equal to V = 40 m^{3}.
2.28. Two thermally insulated vessels 1 and 2 are filled with air and connected by a short tube equipped with a valve. The volumes of the vessels, the pressures and temperatures of air in them are known (V_{1}, p_{1}, T_{1} and V_{2}, p_{2}, T_{2}). Find the air temperature and pressure established after the opening of the valve.
2.29. Gaseous hydrogen contained initially under standard conditions in a sealed vessel of volume V = 5.0 l was cooled by ΔT = 55 K. Find how much the internal energy of the gas will change and what amount of heat will be lost by the gas.
2.30. What amount of heat is to be transferred to nitrogen in the isobaric heating process for that gas to perform the work A = 2.0 J?
2.31. As a result of the isobaric heating by ΔT = 72 K one mole of a certain ideal gas obtains an amount of heat Q = 1.60 kJ. Find the work performed by the gas, the increment of its internal energy, and the value of γ = C_{p}/C_{V}.
2.32. Two moles of a certain ideal gas at a temperature T_{0} = 300 K were cooled isochorically so that the gas pressure reduced n = 2.0 times. Then, as a result of the isobaric process, the gas expanded till its temperature got back to the initial value. Find the total amount of heat absorbed by the gas in this process.
2.33. Calculate the value of γ = C_{p}/C_{V} for a gaseous mixture consisting of ν_{1} = 2.0 moles of oxygen and ν_{2} = 3.0 moles of carbon dioxide. The gases are assumed to be ideal.
2.34. Find the specific heat capacities c_{v} and c_{p} for a gaseous mixture consisting of 7.0 g of nitrogen and 20 g of argon. The gases are assumed to be ideal.
2.35. One mole of a certain ideal gas is contained under a weightless piston of a vertical cylinder at a temperature T. The space over the piston opens into the atmosphere. What work has to be performed in order to increase isothermally the gas volume under the piston n times by slowly raising the piston? The friction of the piston against the cylinder walls is negligibly small.
2.36. A piston can freely move inside a horizontal cylinder closed from both ends. Initially, the piston separates the inside space of the cylinder into two equal parts each of volume V_{0}, in which an ideal gas is contained under the same pressure p_{0} and at the same temperature. What work has to be performed in order to increase isothermally the volume of one part of gas η times compared to that of the other by slowly moving the piston?
2.37. Three moles of an ideal gas being initially at a temperature T_{0} = 273 K were isothermally expanded n = 5.0 times its initial volume and then isochorically heated so that the pressure in the final state became equal to that in the initial state. The total amount of heat transferred to the gas during the process equals Q = 80 kJ. Find the ratio γ = C_{p}/C_{V} for this gas.
2.39. One mole of oxygen being initially at a temperature T_{0} = 290 K is adiabatically compressed to increase its pressure η = 10.0 times. Find:
2.40. A certain mass of nitrogen was compressed η = 5.0 times (in terms of volume), first adiabatically, and then isothermally. In both cases the initial state of the gas was the same. Find the ratio of the respective works expended in each compression.
2.41. A heatconducting piston can freely move inside a closed thermally insulated cylinder with an ideal gas. In equilibrium the piston divides the cylinder into two equal parts, the gas temperature being equal to T_{0}. The piston is slowly displaced. Find the gas temperature as a function of the ratio η of the volumes of the greater and smaller sections. The adiabatic exponent of the gas is equal to γ.
2.42. Find the rate v with which helium flows out of a thermally insulated vessel into vacuum through a small hole. The flow rate of the gas inside the vessel is assumed to be negligible under these conditions. The temperature of helium in the vessel is T = 1,000 K.
2.43. The volume of one mole of an ideal gas with the adiabatic exponent γ is varied according to the law V = a/T, where a is a constant. Find the amount of heat obtained by the gas in this process if the gas temperature increased by ΔT.
2.44. Demonstrate that the process in which the work performed by an ideal gas is proportional to the corresponding increment of its internal energy is described by the equation pV^{n} = const, where n is a constant.
2.45. Find the molar heat capacity of an ideal gas in a polytropic process pV^{n} = const if the adiabatic exponent of the gas is equal to γ. At what values of the polytropic constant n will the heat capacity of the gas be negative?
2.46. In a certain polytropic process the volume of argon was increased α = 4.0 times. Simultaneously, the pressure decreased β = 8.0 times. Find the molar heat capacity of argon in this process, assuming the gas to be ideal.
2.47. One mole of argon is expanded polytropically, the polytropic constant being n = 1.50. In the process, the gas temperature changes by ΔT = 26 K. Find:
2.48. An ideal gas whose adiabatic exponent equals γ is expanded according to the law p = αV, where α is constant. The initial volume of the gas is equal to V_{0}. As a result of expansion the volume increases η times. Find:
2.49. An ideal gas whose adiabatic exponent equals γ is expanded so that the amount of heat transferred to the gas is equal to the decrease of its internal energy. Find:
2.51. An ideal gas with the adiabatic exponent γ undergoes a process in which its internal energy relates to the volume as U = aV^{α}, where a and α are constants. Find:
2.52. An ideal gas has a molar heat capacity C_{v} at constant volume. Find the molar heat capacity of this gas as a function of its volume V, if the gas undergoes the following process:
2.53. One mole of an ideal gas whose adiabatic exponent equals γ undergoes a process p = p_{0} + α/V, where p_{0} and α are positive constants. Find:
2.54. One mole of an ideal gas with heat capacity at constant pressure C_{p} undergoes the process T = T_{0} + αV, where T_{0} and α are constants. Find:
2.55. For the case of an ideal gas find the equation of the process (in the variables T, V) in which the molar heat capacity varies as:
2.56. An ideal gas has an adiabatic exponent γ. In some process its molar heat capacity varies as C = α/T, where α is a constant. Find:
2.57. Find the work performed by one mole of a Van der Waals gas during its isothermal expansion from the volume V_{1} to V_{2} at a temperature T.
2.60. Two thermally insulated vessels are interconnected by a tube equipped with a valve. One vessel of volume V_{1} = 10 l contains ν = 2.5 moles of carbon dioxide. The other vessel of volume V_{2} = 100 l is evacuated. The valve having been opened, the gas adiabatically expanded. Assuming the gas to obey the Van der Waals equation, find its temperature change accompanying the expansion.
