What You Need to Know

Key Concept Diagram

The First Law: energy is conserved; it cannot be created or destroyed, only transformed

The Second Law: in any energy transfer, some energy is degraded to less useful forms (entropy increases)

Entropy is a measure of disorder; natural processes tend towards greater entropy

No machine can be 100% efficient because some energy is always lost as heat (thermal energy)

Key Vocabulary

First Law of Thermodynamics

Energy cannot be created or destroyed; total energy is always conserved

Second Law of Thermodynamics

In any process, entropy tends to increase; no energy conversion is 100% efficient

Entropy

A measure of disorder or randomness in a system; it tends to increase over time

Thermal energy

Internal energy related to the temperature of a substance; the form to which other energies are ultimately degraded

Knowledge Check

Select the correct answer for each question. Click "Check Answer" to see if you are right.

Question 1

A car engine converts chemical energy from fuel into kinetic energy. Some energy is lost as exhaust heat. Which law explains this loss?

First Law: energy is conserved so no loss occurs Second Law: some energy is always degraded to heat in any energy conversion Newton's Third Law Ohm's Law

Question 2

You drop a glass and it shatters on the floor. According to the Second Law, which is true?

The glass could spontaneously reassemble using the same energy The energy in the fall was destroyed The shattered glass will not spontaneously reassemble because this would decrease entropy Entropy decreases when objects break

Question 3

A power station is 35% efficient. This means:

35% of the fuel is wasted 65% of the chemical energy in fuel is converted to useful electrical energy The station operates at 35 degrees Celsius 35% of the chemical energy in fuel is converted to useful electrical energy

Laws of Thermodynamics