l. True or False: For heat engines w cycle, reversible cycle, irreversible 2. Tr
ID: 500525 • Letter: L
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l. True or False: For heat engines w cycle, reversible cycle, irreversible 2. True or False: All pure substances must have S-0 at T-0 K 3. True or False: The maximum theoretical efficiency engine can either increase or decrease of a reversible heat if the working substance is a real gas instead of an ideal gas 4. A reversible process is carried out on an ideal gas NOT under constant pressure conditions. Given that process AS 0 and AH 0 a. the system absorbs heat and expands during the process. b. the system absorbs heat and contracts during the process c. e system loses heat and expands during the process d. the system loses heat and contracts during the process. e. cannot be determined from the information given. 5. Hydrothermal systems in the 20th century used naturally occurring hot water or steam to power electricity generators. Since the 1970s, geothermal energy systems have been developed to pump water to extract heat from underground hot rock that returns as superheated water or steam to drive generators. To be cost-effective the temperature for the hot water and steam is typically at least 120°C (but can range up to 370°C). Consider a system operating with the hot water at 120 oC (hot reservoir). After the heat is extracted for energy, the water is at a temperature of about 35°C (cold reservoir) when returned to the well. What is the maximum theoretical eficiency and power generated from a system for which 10 MW of heat a produced into the cold reservoir? 6. sketch the indicator diagram of four-step heat engine (where a monatomic ideal gas is the working a substance) made up of only reversible adiabatic expansions and compressions plus reversible isochoric steps starting with an adiabatic expansion from state a to b and then isochoric cooling from state b to c. Indicate which steps are adiabatic and which steps are isochoric, and whether a given step represents an expansion or compression. Indicate which states at the end of each step have T hot and which have T T coldExplanation / Answer
1) TURE for heat engines [w cycle reversible] > [w cycle irreversible] the maximum work can be obtain from a heat engine in reversible case- Carnot theorem)
2) TURE All pure substances must have S=0 at T=0K
(The third law of thermodynamics states that at zero Kelvin the entropy is zero for all pure substance.
3) FALSE (The maximum theoretical efficiency for reversible heat engine is decreases, if working substance is real gas instead of ideal gas. Real gases have friction, so heat is lost.
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