Heat Engines and the Second Law of Thermodynamics quiz Flashcards
Heat Engines and the Second Law of Thermodynamics quiz
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Why is thermal energy produced not generally usable to do work?
Thermal energy is not generally usable to do work because, according to the second law of thermodynamics, it is impossible for a heat engine to convert all input heat into work without expelling waste heat. This means that some of the thermal energy must always be lost to a cold reservoir, making 100% efficiency unattainable. Which statement most accurately describes the second law of thermodynamics?
The second law of thermodynamics states that it is impossible for a heat engine to convert all input heat into work without expelling waste heat to a cold reservoir. This implies that no heat engine can be 100% efficient, and a perpetual motion machine of the second kind is impossible. What is a heat engine and how does it function?
A heat engine is a device that converts heat energy into useful work by taking in heat from a hot reservoir, performing work, and expelling waste heat to a cold reservoir. How does the first law of thermodynamics apply to heat engines?
In heat engines, the first law of thermodynamics states that the work done is equal to the heat added minus the waste heat expelled, as the change in internal energy over a cycle is zero. What is the formula for calculating the efficiency of a heat engine?
The efficiency of a heat engine is calculated as the ratio of work output to heat input, represented as W/Q_H or 1 - Q_C/Q_H. Why can't a heat engine be 100% efficient according to the second law of thermodynamics?
The second law of thermodynamics states that it is impossible for a heat engine to convert all input heat into work without expelling waste heat, making 100% efficiency unattainable. What is the role of the hot and cold reservoirs in a heat engine?
The hot reservoir provides the heat energy input to the engine, while the cold reservoir receives the waste heat expelled from the engine. How is the work done by a heat engine related to the heat added and expelled?
The work done by a heat engine is equal to the heat added from the hot reservoir minus the heat expelled to the cold reservoir. What is a perpetual motion machine of the second kind, and why is it impossible?
A perpetual motion machine of the second kind is a hypothetical engine that converts all heat into work without waste, which is impossible due to the second law of thermodynamics. How do you calculate the waste heat expelled by a heat engine?
The waste heat expelled by a heat engine is calculated by subtracting the work done from the heat added, using the formula Q_C = Q_H - W.