(d) A chemist puts an open beaker of liquid benzene in a fume hood and heats it
ID: 1310171 • Letter: #
Question
(d) A chemist puts an open beaker of liquid benzene in a fume hood and heats it with an electric heater. He goes to lunch, and when he returns, half of the benzene has boiled off. What is the temperature of the remaining liquid benzene? (Circle one answer.) Cannot be determined with given data 184.8 C 800. IOC 289.5°C 9. (30 pt) A pump draws 37.7 kgs of water from a lake. The water is pumped 100 feet uphill. Is a 15 kW power supply sufficient? The pump is 70% efficient Diagram Goal: Problem Type: Assumptions: 10. (30 pt) 40.9 moles of an ideal gas is placed in a piston and cylinder system. The piston head and the walls of the cylinder are made out of a thin metal. Initially, the gas is at 5 atm and 298 K, and has a volume of 0.2 m and the piston head is held in place by a catch. The catch is released and the gas expands slowly and reversibly to 1 atm. What is the final temperature of the gas? How much heat flows through the walls of the cylinder? Diagram: Goals: Problem Type: Assumptions:Explanation / Answer
d)
The boiling point of benzene is 80.1 C.
The rest of the remaining liquid remains at its boiling temperature i.e. 80.1 C.
9)
100 feet = 30.4 m
Work done by the pump/second = 37.7 * 9.8 * 30.4
= 11231.584 W
Now efficiency is 0.7, hence the actual power required by the pump = 11231.584/0.7
= 16045.12 W
= 16.045 kW
Hence 15kW power supply is not sufficient.
10)
Assumption: As the process is very slow and reversible we can take the expansion to be isothermal by nature.
The final temperature of the gas = 298K(as it is an isothermal process)
Work Done = -nRTln(Pi/Pf)
= -40.9 * 8.314 * 298 * ln(5/1)
= -163088.68 J
Therefore the heat flow inside the container = 163088.68 J
PS: Take care of the sign, it may also be negative.
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