3.5 Thermal Energy Reservoir and Heat Engines

1. What is a thermal energy reservoir?

• A device used to store pressure

• A body that can absorb or supply heat without changing temperature significantly

• A machine that converts heat into work

• A container used for fluid storage

Which of the following is an example of a thermal energy reservoir?

• Car engine piston

• Steam turbine blade

• Atmosphere (surrounding air)

• Compressor valve

A heat engine operates by:

• Converting all heat into work

• Producing heat from work only

• Receiving heat from a high-temperature source, producing work, and rejecting some heat to a low-temperature sink

• Storing heat permanently

According to the Kelvin-Planck statement, a heat engine cannot:

• Produce work

• Reject heat to surroundings

• Have 100% thermal efficiency

• Operate in a cycle

Why is it impossible for a heat engine to achieve 100% efficiency?

• Some heat must always be rejected to a low-temperature reservoir

• Heat engines cannot produce work

• Friction prevents engine operation

• Pressure cannot be increased

The Clausius statement explains that heat cannot naturally flow:

• From hot body to cold body

• Between objects of equal temperature

• From low-temperature body to high-temperature body without external work

• In an insulated system

Which device is an application of the Clausius statement?

• Steam boiler

• Refrigerator

• Turbine

• Internal combustion engine

If a heat engine receives 1200 kJ of heat and produces 450 kJ of work, what is its thermal efficiency?

• 25%

• 37.5%

• 45%

• 60%

In a heat engine, the rejected heat is transferred to:

• High-temperature reservoir only

• Working fluid only

• Low-temperature reservoir

• Vacuum chamber

Which statement best describes the Second Law of Thermodynamics?

• Energy cannot be created or destroyed

• Heat naturally flows from cold to hot body

• Not all heat energy can be converted into useful work

• Pressure is inversely proportional to volume