# AP Environmental Science : Laws of Thermodynamics

## Example Questions

### Example Question #1 : Laws Of Thermodynamics

Most automobiles today have an energy efficiency of roughly 25% to 30%, meaning only a fraction of the potential energy from the gas you pump into your car will be converted into the kinetic energy of the car actually moving. Which of the following statements is true and best explains this phenomenon?

Possible Answers:

Energy cannot be created, but it can be destroyed in the process of converting to another form.

Energy cannot be destroyed, but it can be created.

Energy can be neither created nor destroyed.

Energy can be converted from one form to another but no energy is lost in this process.

When energy is converted to another form, the energy quality will decrease and energy cannot be recycled to a higher efficiency.

Correct answer:

When energy is converted to another form, the energy quality will decrease and energy cannot be recycled to a higher efficiency.

Explanation:

The second law of thermodynamics states that when energy is converted from one form to another, some energy is lost and efficiency decreases. The energy from gasoline igniting is lost to friction from the engine and converting energy in the form of a combustion to the form of wheels rotating forward. Efficiency of energy use is lost in this conversion process.

### Example Question #1 : Laws Of Thermodynamics

Which Law of Thermodynamics explains how Earth is an open system?

Possible Answers:

The First Law because no energy escapes from Earth, it stays on the planet indefinitely.

The Second Law because the Sun provides energy to the Earth, thus making it unable to be an isolated system.

The First Law because all energy on Earth originates from the Sun.

The Second Law because the entropy on Earth can only increase.

Correct answer:

The Second Law because the Sun provides energy to the Earth, thus making it unable to be an isolated system.

Explanation:

The Second Law of thermodynamics states that the entropy on Earth can only increase unless there is an external source of energy. This external source is the Sun, which makes Earth an open system. Energy is able to flow both into an out of the Earth's energy system and explains phenomena such as evolution and global warming.