Chapter 14Heat and Temperature

Temperature

• Is a measure of how hot (or cold) a substance is

• A measure of the average kinetic energy of the particles in an object– The temperature of a substance is proportional

to the average kinetic energy of the substance’s particles

– All particles have kinetic energy• Particles that are hot move faster than cold particles

Temperature

• Some Thermometers use the expansion of liquids (mercury/alcohol) to measure temperature– These liquids expand

as their temperature increases and contract as their temperature falls

Temperature• Digital thermometers

(Thermoresistor)– Have a semiconductor that acts

like a temperature-sensitive electric resistor

– At low temperature is essentially a n insulator

• No mobile electric charges– At higher temperatures (98),

thermal energy rearranges the charges in the thermistor and it has more mobile electric charges

• Ability to conduct electricity increases

• Uses liquid crystals base display

Temperature

• Thermostats rely on the expansion of different metals– Coil made of two

different metal strips• Expand at different

rates when temperature increases

• Contract at different rates when temperature decreases

Temperature

Temperature

Temperature

Temperature

• Temperature scales– Fahrenheit (0F): water freezes at 320F and boils

at 1000F– Celius (Centigrade) (0C): water freezes at 00C

and boils at 1000C– Kelvin (0K): is based on absolute zero

• No kinetic energy (no movement)• Freezing temperatures in the F/C scale there is still

kinetic energy

Temperature

• C to F conversions:– TF = 1.8TC + 32.0– Example: 400C = ______ 0F– 1.8 x 400C + 32.0 = 72 + 32.0 = 1040F

• F to C conversions:– TC = TF – 32.0 / 1.8– Example: 500F = ______ 0C– 500F – 32.0 / 1.8 = 18/1.8 = 100C

Temperature• C to F conversions:

– +40 x 9/5 – 40 =– Example: 400C = ______ 0F– 40 + 40 x 9/5 – 40 =– 80 x 9/5 - 40 = 144 – 40 = 1040F

• F to C conversions:– +40 x 5/9 – 40 =– Example: 500F = ______ 0C– 40 + 50 x 5/9 – 40 =– 90 x 5/9 – 40 = 50-40= 100C

Temperature

• Works because at -40 F = C and C = F• -400C = _____ 0F• -400C + 40 x 9/5 – 40 = 0 x 9/5+40 = 0-40 = -400F

• -400F = ______0C• -400F + 40 x 5/9 – 40 = 0 x 5/9 + 40 = 0-40 = -

400C

Temperature

• Kelvin scale is based on absolute zero– Theoretical lowest temperature is -273.150C– Kinetic energy of the object would be zero– 0 K = -2730C– TK = TC + 273

Temperature

Temperature

Temperature

• The highest temperature ever recorded on Earth was 57.80C in Libya, 1922. Convert this to Fahrenheit and Kelvin.

• 57.80C + 40 x 9/5 – 40 =• 97.8 x 9/5 – 40 =• 176.04 – 40 =• 136.040F

• 57.80C + 273 = 330.8 = 3310K

Temperature

Temperature

Temperature

Temperature

• Temperature changes indicate an energy transfer– The energy transferred between the particles of

two objects because of a temperature difference between two objects is called heat

• This transfer of energy is always from something at a higher temperature to something at a lower temperature

Temperature

Temperature

Temperature

Energy Transfer

• Heat energy can be transferred in three ways:– Conduction– Convection– Radiation

Energy Transfer• Conduction: occurs

between objects in direct contact– Takes place when objects

that are in direct contact are at unequal temperatures

– Transfer of energy as heat through a material

– Rapidly moving particles in one object transfer some of their energy to slowly moving particles of another object

Energy Transfer• Convection: results from

the movement of warm fluids– Energy transfer resulting

from the movement of warm fluids

– ONLY possible in fluids• Most fluids are liquids or

gases• Convection currents: they

cycle of heated fluid that rises and then cools and falls

Energy Transfer

Energy Transfer

Energy Transfer

Energy Transfer

• Radiation:– Does not require physical contact

• Does not involve the movement of matter across space• Only energy that can be transferred through a vacuum

– Electromagnetic waves, which includes infrared radiation, visible light, and ultraviolet rays

– Energy is transferred as electromagnetic waves• When substances absorb the energy of the waves the kinetic

energy of the molecules increase and thus their temperature increases

Energy Transfer

Energy Transfer

Energy Transfer

Energy Transfer

• Infrared thermography is equipment or method, which detects infrared energy emitted from object, converts it to temperature, and displays image of temperature distribution.

• It captures as a temperature distribution on a surface, and it can display as a visible information.

Energy Transfer

Energy Transfer

• Conductor: is a material through which energy can be easily transferred as heat

Energy Transfer

• Insulator: is a material that transfer energy poorly

Energy Transfer

Energy Transfer

• Specific Heat: the quantity of heat required to raise a unit mass of homogeneous material 1 K or 10C in a specified way given constant pressure and volume

• Amount of energy required to raise the temperature of 1 Kg by 1K – Is a physical property of matter– Represented by symbol c (J/kgxK)

Energy Transfer

Energy Transfer

• Specific heat can be used to figure out how much energy it takes to raise an object’s temperature

• Energy = specific heat x mass x temperature change• Energy = c x m x change in temp

– c = 4,186J/KgK

• How much energy must be transferred as heat to 200 kg of water in a bathtub to raise the water’s temperature from 250C to 370C– Energy = 4,186J/KgK x 200Kg x 12K– Energy = 10,000,000J = 1.0 x 107J

Energy Transfer

• Heat changes an object’s temperature or changes the object’s state– Added energy either raises its temperature or

changes its state, not both at the same time

Energy Transfer

Energy Transfer

Energy Transfer• The freezing point or melting point of water is the

temperature at which water changes phase from a liquid to a solid or vice versa. The freezing point describes the liquid to solid transition while the melting point is the temperature at which water goes from a solid (ice) to liquid water. In theory, the two temperatures would be the same, but liquids can be supercooled beyond their freezing points so that they don't solidify until well below freezing point. Ordinarily the freezing point of water is 0° C or 32° F. The temperature may be lower if supercooling occurs or if there are impurities present in the water which could cause freezing point depression to occur.

Energy Transfer

• The boiling point of water depends on the atmospheric pressure, which changes according to elevation. The boiling point of water is 100°C or 212° F at 1 atmosphere of pressure (sea level), but water boils at a lower temperature as you gain altitude (e.g., on a mountain) and boils at a higher temperature if you increase atmospheric pressure (lived below sea level).

Using Heat

• First Law of Thermodynamics states that the total energy used in any process is conserved, whether that energy is transferred as a result of work, heat, or both.

• Second Law of Thermodynamics states that the energy transferred as heat always moves from an object at a higher temperature to an object at a lower temperature.

Using Heat

• Entropy: a measure of the randomness or disorder of a system

Using Heat• The second law of thermodynamics states that energy has

the tendency to disperse unless it is inhibited from doing so. The reason the second law is essential to the understanding of entropy is because it explains its basics. However, entropy is loosely defined as the disorder (and order) in a particular system or process. It studies the fluctuation - slowing, cooling, heating, and exhaustion - that occurs in natural processes. Since scientifically, the term "entropy" is quite loosely defined, here are five examples of entropy to aid in your understanding of one of the most important scientific concepts.

Using Heat• Heating and Cooling of Water• In order to heat water, it needs to be exposed to heat

energy for some time. This energy is transferred to the particles in water, gradually causing them to vibrate at a faster rate. Additionally, the particles' motion also increases in speed; they begin to zoom across the container in a random and disorderly manner. The change in how the particles move and vibrate causes the temperature of the water to increase. However, the opposite of this behavior is also observed when the water is no longer exposed to heat energy. The particles gradually decrease in speed and the intensity of vibration becomes smaller. As a result, the water cools down with time.

Using Heat• Electrons in Atomic Shells• Electrons would actually escape from their atomic

shells if they could. However, the nucleus of the atom ensures that electrons continuously revolve around it. This is due to the fact that electrons are negatively charged, while the nucleus is positively charged, they attract each other and the atom remains intact. However, if the nucleus were to be extracted from the atom, the electrons would definitely zoom out of their shells and disperse into their surroundings.

Using Heat

• Life and Death• Believe it or not, a prevalent example of entropy is

the life cycle of animals. After you are born, your body slowly begins to grow larger, stronger, and more able with time. However, this does not remain the case. After some time, the body becomes weaker, bones turn brittle, and you become less competent in living daily human life. This shows how ultimately, an animal's body is gradually exhausted until death takes place.

Using Heat• Climate Change• You have probably been made aware of global warming, a

rise in the Earth's climate that is expected to occur in the near future. However, climate change has been a natural phenomenon ever since the Earth came into existence. An earlier example is the ice age. It took place at the end of the Mesozoic era (when dinosaurs went extinct) and lasted approximately 110,000 years. Global warming, on the other hand, will mean that the earth's climate is about to raise above the norm as opposed to the ice age.

Using Heat• The Sun's Exhaustion• The sun is like any other star; it goes through a life cycle.

As a result, its energy is by no means infinite. The sun runs on fuel consistent predominantly of hydrogen that burns at its core. However, this supply of hydrogen will someday deplete, which means the sun will no longer be able to produce heat. Also, gravity will no longer be able to support it, causing the sun to expand into a fiery ball of gas called a red giant. Ultimately, this energy will disperse across space until it gradually transforms into a white dwarf.

Using Heat

• As you can see, entropy is, in fact, a massive part of life in our universe. From the temperature of water to the state our sun exists in, entropy seems to be detrimental to all of it. As a result, it is important to study and understand entropy so that it is easier to understand our surroundings and how and why things came to be the way they are. Hopefully, the examples above clarified the definition of entropy and what a critical scientific concept it actually is.

Using Heat

• Heat Engines:– Chemical energy is converted to mechanical

energy through the process of combustion– Internal-combustion engines burn fuel inside

the engine• Always generate heat

Using Heat