# 3. Energy (13 lessons)

#### Concepts

• Energy is movement or the ability to produce movement.
• Energy can take many forms, but the forms we will focus on in this course are chemical potential energy (positional), thermal kinetic energy (heat), and electromagnetic energy (radiation).
• (First law of thermodynamics): in a closed system, no matter what processes occur, the total amount of energy will be conserved.
• Kinetic energy is the energy of motion.  Thermal kinetic energy is the energy of motion at the molecular level – the faster particles are moving inside a sample, the more thermal kinetic energy it has.
• The temperature (in Kelvins) of a sample is proportional to its thermal kinetic energy.  Therefore, we can indirectly measure thermal kinetic energy with a thermometer.
• (Second law of thermodynamics): if two substances of different temperatures are placed in contact with each other, heat will flow from the hotter substance to the colder substance until they reach thermal equilibrium.
• As a sample is heated, its temperature increases. But during phase transitions, the added thermal energy is transformed into electrostatic potential energy as intermolecular bonds are broken.  This “lost” energy is called latent heat.
• A photon is the smallest possible “package” of electromagnetic radiation, and can be thought of as both a particle and a wave.  Higher-energy photons have higher frequencies.
• An atom absorbs/emits a photon when one of its electrons moves to a higher/lower energy orbit.

# Skills

Quiz 3a

• Understand heat as the energy of moving molecules
• Solve problems involving conservation of energy and latent heat, using energy transfer diagrams.

Quiz 3b

• Draw the Bohr model of an atom in an excited or ground state.
• Use the equation E=hf to determine the energy of a photon based on its frequency, and vice versa.
• Determine the type of radiation produced when an electron drops between given energy levels; or determine the level of excitement of an electron that absorbs a photon of a given frequency.

Quiz 3a

Quiz 3b

Quiz 3a

Quiz 3b

#### Assessment

• Quiz 3a: Kinetic molecular theory, heat capacity, latent heat
• Quiz 3b: Photon emission and absorption.
• Test 3: Energy