1. A block of ice of mass 0.4 kg and initial temperature T = 0 o C is placed in
ID: 1306980 • Letter: 1
Question
1.
A block of ice of mass 0.4 kg and initial temperature T = 0 oC is placed in a sealed insulated container full of Helium gas, initially at temperature 220 oC and pressure of 1 atm. The volume of the Helium is 720 L, and is constant. Helium is a monatomic ideal gas.
What is the mass of the liquid water when the system comes to equilibrium? (In other words, how much ice melts?)
Assume no heat is lost to the surroundings.
Give your answer in kg to three significant digits.
2.
An expandable cylinder filled with neon, a monatomic ideal gas, initially has a volume of 4.5 L at 1.5 atm and 40 oC. Thermal energy is slowly added to the gas until the volume is 12.0 L but the pressure remains constant.
What is Ef - Ei, the change in the thermal energy during this expansion?
WARNING: Beware of units! You should always use -
For Volume use Cubic Meters, m3: 1 m3 = 103 L
For pressure use Pascals, Pa: 1 atm = 1.01 x 105 Pa
For temperature use Kelvin, K: 1 K = 1 oC (same unit "size") but TK = TC + 273 K
kB = 1.38 x 10-23 J/Kelvin (but you probably don't need this).
Give your answer to 3 digits, in Joules.
3.
An "Isentropic" change in a system is one where the entropy doesn't change (approximately). In gases, this can happen if changes are made faster than energy can flow in or out of the gas due to the temperature difference with the surroundings. For example, sound waves and the winds blowing down the sides of mountains are often modeled as being constant entropy.
Consider air traveling down the California coastal mountains, starting at a height of 3000 m and an atmospheric pressure of 70 kPa and temperature of 6 oC down to sea level. What is the temperature of the air when it reaches Los Angeles at sea level (air pressure of 101 kPa)?
Give your answer in oC to three digits.
Your Answer:
4.
A 7 L rigid (constant volume) container holds 0.62 moles of helium at an initial temperature of 60 oC. The container has a pressure release valve that keeps the gas pressure constant as the temperature of the gas changes. The container is heated so that the temperature of the gas increases to 203 oC.
How many moles of gas will be in the container at the final temperature?
Give your answer to three significant figures.
Your Answer:
5.
A flexible container of ideal gas, made up of more complex molecules, has the thermal (internal) energy given by
Eth = 3.7 * n * R * T
The gas is initially at pressure Pi= 1.5 x 105 Pa, Volume Vi= 3 Liters, and temperature Ti = 295 K. An amount of energy as heat, Q = - 500 J, is removed from the gas by placing the container in a refrigerator. During this process, the gas is held at constant pressure as the energy is removed.
What is the magnitude of the change in temperature of the gas due to the removal of the energy?
Give your answer in Kelvin to three significant digits. Do not include the units in your answer. Your answer should be positive (magnitude).
Your Answer:
6.
You are designing a process to store pressurized argon gas (a monatomic gas). You start with 7 moles of argon at a temperature of 290 K and 1 atm. You want the final pressure of the gas to be 19 atm.
If you pressurize the gas at a constant temperature, how much work must be done on the gas?
Give you answer in Joules to four significant digits.
7.
What is the molar density (moles per unit volume) of a an ideal gas at 21 oC and 2 atmospheres?
Give your result in moles/m3 to three significant figures .
Explanation / Answer
2. To find number of mols of neon we use the relationship PV=nRT
(1.5atm)(4.5L) = n(.0821atm.L/mol.K)(313K)
n = .263mols
From the formula to find change in thermal energy: W= nRT ln(Vf/Vi)
We have W= 656.787J
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