Chapter 9 Notes - Thermodynamics

​Chapter 9 - Thermodynamics

Open Ended

What is a calorie?

Open Ended

What type of energy do we burn?

Open Ended

So if you release heat due to chemical breakdown of molecules and movement of blood in your body, then how do you think calorie can be used in thermodynamics?

Open Ended

Remember from meteorology that all natural systems want to be balanced. For weather to become balanced, what would have to happen between the warm and cool air masses merging onto each other? For example, if one air masses temperature is 47 degrees F and another is 87 degrees F, and if they were merging together, how would they eventually balance out?

• What is heat?

• How is it produced?

• How is it measured?

• How do we use it?

• Could the sun be a reliable, inexhaustible source of energy?

​​Chapter 9 - Thermodynamics

Early Theories of Heat...
Sixth century BC: Greek Philosopher Heraclitus claimed there were three natural elements—earth, water, and fire

• Thirteenth century AD: philosophers and scientists thought that motion is the essence of heat

​​Chapter 9 - Thermodynamics

Early Theories of Heat...
This concept was reaffirmed by English philosopher and scientist Francis Bacon

• 18^th century Joseph Black suggested heat was like an invisible fluid

  • Solids needed to be filled up with this heat-fluid until they melted

​​Chapter 9 - Thermodynamics

Early Theories of Heat...
French chemist Lavoisier developed this idea and called the heat-fluid “caloric”

• The caloric theory was successful in observations and predictions

• Theory of steam engines in early 1800s by Nicholas Sadi Carnot - example of thermal heat and work capacity.

​​Chapter 9 - Thermodynamics

​​Chapter 9 - Thermodynamics

Early Theories of Heat...
Carnot’s work evolved into the science of modern thermodynamics

• The study of thermal energy and heat and how they relate to other kinds of energy and work

• Carnot cycle is the ideal cycle, in which heat is generated, or added, at a constant temperature and rejected at a lower temperature.

​​Chapter 9 - Thermodynamics

Early Theories of Heat...
Benjamin Thompson was first to discount the caloric theory 

• Observed during military training  cannons fired without cannonballs became much hotter than those that fired normally

​​Chapter 9 - Thermodynamics

Early Theories of Heat...
If the caloric theory were true, release of caloric and resulting temperature rise should have been unaffected by the cannonball when the gunpowder was fired

• Rumsford (Thompson) observed a dull boring bit could generate more heat

​​Chapter 9 - Thermodynamics

Early Theories of Heat...
If the caloric theory were true, release of caloric and resulting temperature rise should have been unaffected by the cannonball when the gunpowder was fired

• Rumsford (Thompson) observed a dull boring bit could generate more heat

​​Chapter 9 - Thermodynamics

Multiple Choice

• Which scientist first challenged the caloric theory through experiments?

• Antonie Lavoisier

• Nicholas Sadi Carnot

• Benjamin Thompson

​​Chapter 9 - Thermodynamics

• Julius Robert von Mayer was first to experiment with the idea of heat as energy (not as matter) in 1842

• Mayer used a horse-powered mechanism to stir a pot of paper pulp

  • Calculated mechanical energy needed to heat mixture

  • Demonstrated mechanical energy could be converted to thermal energy

​​Chapter 9 - Thermodynamics

• James Prescott Joule: clear connection between mechanical energy and heat

• Did experiments using mechanical devices that were dropped, shaken, and stirred to produce changes in temperature of liquids and gases 

​​Chapter 9 - Thermodynamics

• James Prescott Joule: clear connection between mechanical energy and heat

• Did experiments using mechanical devices that were dropped, shaken, and stirred to produce changes in temperature of liquids and gases 

• Joule concluded that the equivalent of 4.18 N•m of mechanical work would raise the temperature of 1 g of water
  1 °C 

• Established that energy causes temperature changes in matter

Multiple Choice

Which scientist first showed a clear connection between mechanical energy and heat?

• Robert Mayer

• James Prescott Joule

• William Thompson

Early Theories of Heat...
Kinetic-molecular model: atoms, molecules, ions, and subatomic particles are in constant motion and have kinetic energy

• Internal energy of matter - Sum of all potential and kinetic energies in a substance

  • Cannot be measured

​​Chapter 9 - Thermodynamics

Multiple Choice

The sum of all potential and kinetic energies in a substance is called its

• external energy

• internal energy

• heat

• temperature

Early Theories of Heat...
Kinetic molecular theory states that gas particles are in constant motion and exhibit perfectly elastic collisions, meaning elastic collision is an encounter (collision) between two bodies in which the total kinetic energy of the two bodies remains the same

Example: Phet Simulation on Gases

​​Chapter 9 - Thermodynamics

​​Chapter 9 - Thermodynamics

Warm systems move towards cool systems due to density differences due to temperature and pressure!

​​Chapter 9 - Thermodynamics

​​Chapter 9 - Thermodynamics

​High pressure "chases" Low Pressure

​​Chapter 9 - Thermodynamics

​​Chapter 9 - Thermodynamics

Why do we study this???
For a renewable energy source to be valuable, it must be able to convert its energy into a useable form

• Solar panels can change sunlight directly into electricity 

​​Chapter 9 - Thermodynamics

• Energy costs continue to rise

  • Is there a more economical way of converting the free energy of the sun into electricity?

  • Solar thermal (ST) power plant

    • Mojave Desert, California

Open Ended

Why do you think that solar panels are still not the most beneficial resource for energy in this current time period?

​​Chapter 9 - Thermodynamics

Part 2 - How do we measure heat? Temperature

​

​A measurement that describes the average kinetic energy in random thermal motion per atom or molecule

​Temperature

Multiple Choice

Temperature is a measure of the...

• total energy in a substance
• total kinetic energy in a substance
• average potential energy in a substance
• average kinetic energy of molecules in a substance

A calibration tool to measure temperature changes

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3 different scales

Fa​hrenheit

Celsius

​Kelvin- the base unit of temperature in the International System of Units, having the unit symbol K

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​Thermometers

Multiple Choice

A(n) _____________ is a device for measuring temperature.

• thermometer
• barometer
• anemometer
• psychrometer 

• The Fahrenheit Scale

  • Freezing temperature of pure water

  • Boiling temperature of pure water

  • On the Fahrenheit scale there are 180 degrees between water’s freezing point, 32 °F, and boiling point, 212 °F

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​Thermometers

• The Celsius Scale

  • Temperature range between freezing and boiling points of water: 100 degrees

    • Freezing: 0 °C

    • Boiling: 100 °C

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​Thermometers

​is produced when a rise in temperature causes atoms and molecules to move faster and collide with each other

​Thermal Energy

Multiple Choice

When thermal energy is added to a substance, the substance's particles move:

• More rapidly at an increased diestance from each other.
• More rapidly with less distance between each other.
• More slowly with a greater distance between each other.
• More slowly with a reduced distance between each other.

How to Convert Temperature Scales?

Multiple Choice

Convert 101 degrees F to degrees C

• 34 degrees C

• 38 degrees C

• 42 degrees C

Multiple Choice

Convert -38.9 degrees C to Kelvin

• 234.3 K

• 244.5 K

• 293.8 K

the energy associated with the random, disordered motion of molecules within the system

ENTROPY ​

​the degree of disorder or randomness in the system...

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​Internal Energy

ENTROPY ​

​the degree of disorder or randomness in the system...

Entropy is a measure of how much the atoms in a substance are free to spread out, move around, and arrange themselves in random ways. For instance, when a substance changes from a solid to a liquid, such as ice to water, the atoms in the substance get more freedom to move around.

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​Internal Energy

Multiple Choice

As a system becomes more disordered, entropy

• remains the same
• increases
• decreases
• cannot be determined

• “Heat” is often used for both thermal energy and temperature

  • Neither is scientifically correct

• The amount of thermal energy in an object is a property of the object—it has thermal energy

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​Heat and Entropy

The more disorganized the molecules are the higher state of entropy

Entropy increases as temperature increases​

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Entropy is a measure depending on the disorganization

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​Entropy and States of Matter

Multiple Choice

Do molecules generally move faster at 45 C or 106 C?

• 45 C because molecules have more energy than in 106C

• 106 C because molecules have more energy than in 45C

• 106 C because molecules have less energy than in 45C

• 45C because molecules have less energy than in 106 C

Multiple Choice

Which statement is true about the ENTROPY?

• Entropy refers to DISORDER, the unusable energy that escapes a system.
• Entropy refers to the balance of temperature among two or more systems.
• Entropy refers to the average kinetic energy of the molecules.
• Entropy refers to the inability to destroy or create energy. 

All kinetic energy stops

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the minimum possible

temperature, 0 K, or −273ºC (−459ºF)

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​Absolute Zero

Multiple Choice

What happens at absolute zero?

• All Motions cease

• everything turns to a solid

• everything dies

• who knows?

Changes both the temperature and the state of matter

​

​Travels from high to low

Heat

0th Law

​Thermal equilibrium

​

The condition under which two substances in physical contact with each other exchange no heat energy

temperatures balance out, heat stops flowing, then the system (or set of systems)​

Laws of Thermodynamics

Multiple Choice

Heat is

• hot
• the energy that is transferred between objects because of a temperature difference

• the quantity measure from the average kinetic energy of vibrating molecules in a substance

Multiple Choice

The temperature of a glass of cold water will eventually...

• Match the temperature of the surrounding environment.
• Always be colder than the surrounding environment.
• Become warmer than the surrounding environment.
• Never change temperature.

1st Law

Conservation of Energy

​

Energy cannot be created or destroyed only changed into another form ​

Laws of Thermodynamics

Multiple Choice

The total amount of energy in a system is ALWAYS ________.

• increasing
• decreasing
• conserved 
• changing

2nd Law

Heat

​

Heat always flows from hot to cold

Laws of Thermodynamics

Multiple Choice

Which way does heat flow?

• hot to cold
• cold to hot
• it doesn't 

Multiple Choice

What is thermodynamics?

• movement of heat
• it's magic
• measurement of heat
• none of them

3rd Law

Entropy

​

​As temperature approaches absolute zero, entropy is at constant minimum

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Laws of Thermodynamics

Multiple Choice

Entropy increases from solid, liquid to gas. Why?

• Molecular disorder increases
• Molecular randomness decreases
• Molecules are more energetic
• Molecules are more reactive

Multiple Choice

What is absolute zero?

• 0 K
• 273 K
• 0^oC

Conduction

​

​the transfer of heat through or between materials by direct contact

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Heat Transfer Method

Multiple Choice

Conduction

• The transfer of thermal energy through solids

• The transfer of thermal energy through liquids and gases

• The transfer of thermal energy as electromagnetic waves

Convection

​

the transfer of heat by the motion of liquids and gases

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Heat Transfer Method

Multiple Choice

Convection

• The transfer of thermal energy through liquids and gases

• The transfer of thermal energy through solids

• The transfer of thermal energy as electromagnetic waves

Multiple Choice

Warm air rises and cold air sinks demonstrates what?

• conduction
• convection
• radiation
• refrigeration

Radiation

​

the dispersal of energy through space through electromagnetic waves

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Heat Transfer Method

Multiple Choice

Heat travels from the sun to the earth by the process of...

• conduction
• convection
• radiation
• insulation

Multiple Choice

Radiation

• The transfer of thermal energy as electromagnetic waves

• The transfer of thermal energy through solids

• The transfer of thermal energy through liquids and gases

​materials that transfer heat readily (ex: diamond, copper, aluminum, gold)

Thermal Conductors

materials that do not transfer heat readily (ex: plastic, wool, styrofoam)

Thermal Insulators

Multiple Choice

What type of material makes the best insulators?

• Aluminum
• Copper
• Styrofoam
• Metal

Multiple Choice

Heat moves easily through materials called ____

• Wood

• Plastic

• Rubber

• Metal

• Heat Capacity

  • Thermal energy, in joules, an object must gain or lose to cause a temperature change of 1 °C

    • Units: J/°C or J/K

How do we measure heat?

How do we measure heat?

How do we measure heat?

How do we measure heat?

​Specific Heat Capacity

• Specific heat (c_sp) is the heat capacity per gram of material—the amount of thermal energy that must be gained  or lost to change the temperature of
  1 g of the substance 1°C 

How do we measure heat?

​Water has an especially high heat capacity at 4.18 J/g*C, which means it takes more heat to warm a gram of water. This is why, throughout the course of a warm summer day, the water in the ocean does not experience a significant change, thus the ocean has high specific heat capacity

Open Ended

Describe in your own words why the ocean has high or low specific heat capacity?

How do we measure heat?

​Water’s heat capacity allows perspiration to be an effective cooling mechanism for our bodies. Thus, when we sweat it is cooling us off!

How do we measure heat?

• When thermal energy is added to or taken from a material, its temperature usually changes because kinetic energy of its atoms and molecules changes

• Sometimes the temperature doesn’t change

How do we measure heat?

• Latent heat of fusion (L_f): the amount of thermal energy exchanged per gram of material during melting or freezing

• Latent heat of vaporization (L_v): the amount of thermal energy exchanged per gram of material during boiling or condensation

How do we measure heat?

• Every substance has a distinctive  specific heat for each of its states

• Every substance has a characteristic latent heat of fusion and of vaporization