3. Energy cannot be created or destroyed, although in many processes energy is transferred

to the environment as heat. As a basis for understanding this concept:

a. Students know heat flow and work are two forms of energy transfer between

systems.

b. Students know that the work done by a heat engine that is working in a cycle is

the difference between the heat flow into the engine at high temperature and the

heat flow out at a lower temperature (first law of thermodynamics) and that this

is an example of the law of conservation of energy.

c. Students know the internal energy of an object includes the energy of random

motion of the object’s atoms and molecules, often referred to as thermal energy.

The greater the temperature of the object, the greater the energy of motion of the

atoms and molecules that make up the object.

d. Students know that most processes tend to decrease the order of a system over

time and that energy levels are eventually distributed uniformly.

e. Students know that entropy is a quantity that measures the order or disorder of a

system and that this quantity is larger for a more disordered system.

f.* Students know the statement “Entropy tends to increase” is a law of statistical

probability that governs all closed systems (second law of thermodynamics).

g.* Students know how to solve problems involving heat flow, work, and efficiency in

a heat engine and know that all real engines lose some heat to their surroundings.

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