Chapter 9.1 “Temperature and Thermal Equilibrium”territorio.s3-website-us-east-1.amazonaws.com/archivos/clases/... · Chapter 9.1 “Temperature and Thermal Equilibrium ... *

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Chapter 9.1 “Temperature

and Thermal Equilibrium” * Defining Temperature

* We associate temperature with how hot or cold

an object feels.

* Our sense of touch serves as a qualitative

indicator of temperature.

* Energy must be either added or removed from

an object to change its temperature.


and Thermal Equilibrium” * Temperature is proportional to the kinetic

energy of atoms and molecules.

* Temperature is a measure of the average kinetic

energy of the particles in a substance.

* A substance temperature increases as a direct

result of added energy being distributed among

the particles of a substance.

* Internal energy is the

energy of a substance due

to both the random motions

of its particles and to the

potential energy that results

from the distances and

alignments between the

particles.

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and Thermal Equilibrium” * Temperature is proportional to the kinetic

energy of atoms and molecules.

* The internal energy of a material is due to the

random motions of its component particles and is

equal to the total energy of those motions.

* The particles can be atoms or molecules, and

they can have three forms of energy:

translational, rotational, and vibrational. .

* Translational energy → is energy that comes

from the horizontal or vertical motion of particles.

* Rotational Energy → is energy that comes from

the rotation or spinning of the particle.

* Vibrational energy → is energy that comes from

the bending or stretching of the bonds within the

particles.


and Thermal Equilibrium” * Kinds of Energy

Visual Concept

http://my.hrw.com/hssc_2012/hmd_na_phy/nsmedia/visualconcepts/70624.htm

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and Thermal Equilibrium” * Thermal expansion

* In general, if the temperature of a substance

increases, so does its volume. This phenomenon is

known as thermal expansion.

* Different substances undergo different amounts

of expansion for a given temperature change.

* The thermal expansion characteristics of a

material are indicated by a quantity called the

coefficient of volume expansion.

* Gases have the largest values for this

coefficient. Solids typically have the smallest

values.



* In general, when the temperature of a material

increases its volume also increases, regardless of

whether the material is a solid, liquid, or gas.

Visual Concept

http://my.hrw.com/hssc_2012/hmd_na_phy/nsmedia/visualconcepts/70625.htm

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* In general, the volume of a liquid tends to

decrease with decrease temperature.

* However, the volume of water increases with

decreasing temperature in the range between 0°C

and 4°C.

* When water freezes, crystal form which have more

empty space between the molecules than the

liquid. This explains why ice floats in liquid water .

* Solids typically have the smallest coefficient of

volume expansion values. For this reason, liquids in a

solid container expand more than the container.

This property allows some liquids to be used to

measure changes in temperature.


and Thermal Equilibrium” * Measuring Temperature

* Temperature is measured in one of three

common temperature scales:

* Celsius Degrees

* Fahrenheit Degrees

* Kelvin

* To have a temperature scale we need to

know the values for:

* The freezing point of pure water

* The boiling point of pure water

* The number of units between them.

* DEGREE is a unit between 2 points in a

temperature scale.

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and Thermal Equilibrium” * Fahrenheit Scale

* Most commonly used in the USA

* Developed in the early 1700’s by Gabriel

Fahrenheit.

* Pure water freezes at 32°F

* Pure water boils at 212°F

* There are 180 equal units or degrees between

the freezing point and boiling point.


and Thermal Equilibrium” * Celsius Scale

* Most commonly used in the rest of the world

* Developed in 1740 by Andre Celsius

* Pure water freezes at 0°C

* Pure water boils at 100°C

* There are 100 equal units or degrees between

the freezing point and boiling point.

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and Thermal Equilibrium” * Kelvin

* Most commonly used in the scientific world.

* Pure water freezes at 273 K

* Pure water boils at 373 K

* There are 100 equal units between the

freezing point and boiling point.

* Kelvin scale of temperature does not use the

suffix degrees.

* Kelvin scale is referred to as the absolute

scale.

* The 0 temperature in the Kelvin Scale is

referred to as the absolute zero.


and Thermal Equilibrium” * Measuring Temperature

* In order for a device to be used as

a thermometer, it must make use of

a change in some physical property

that corresponds to changes in

temperature, such as the volume of

a gas or liquid, or the pressure of a

gas at a constant volume.

* The most common thermometers

use a glass tube containing a thin

column of mercury, colored alcohol,

or colored mineral spirits.

* When the thermometer is heated,

the volume of the liquid expands.

* The change in length of the liquid

column is proportional to the

temperature.

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and Thermal Equilibrium” * Changes in temperature

* Matter exists in one of three states:

* solid * liquid * gas

* Matter can change from one state to another

when there is a change in the kinetic energy or

temperature of the object.

* Melting occurs when a solid becomes a liquid.

* The melting point is the point at which melting

begins.

* Melting begins when the particles of a solid

start vibrating fast enough so that they start

breaking away from one another and become

a liquid.



* Freezing occurs when a liquid turns into a solid.

* The freezing point is the point at which freezing begins.

* At the freezing point, a liquid particle loses energy. They

don’t move as quickly and eventually become a solid.

* The melting point and the freezing point of a substance

are the same.

* Above the freezing / melting point, the substance is a

liquid.

* Below the freezing / melting point, the substance is a

solid.

* At the freezing / melting point, the substance can be

either a liquid or a solid. * The freezing / melting point of water is 0°C

Below

0°C Water is neither solid nor liquid

15°C Water is liquid Above

-15°C Water is solid (ice)

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and Thermal Equilibrium” * Changes in temperature * Evaporation is the process by which a liquid becomes a

gas.

* Particles in liquids move at different speeds. The fastest

moving particles escape from the surface of a liquid

becoming gas.

* Since warmer liquids have faster moving particles,

evaporation occurs more quickly when a substance is

warmer.

* Boiling is another process that allows a liquid to become a

gas.

* When heated, particles within a liquid from bubbles of gas.

When these bubbles of gas start moving fast enough they

rise to the surface of the liquid and escape.

* The boiling point is the point at which a boiling can occur.

* Evaporation can occur at many temperatures, but boiling

can occur only at or above the boiling point.

* The boiling point of water is 100°C.


and Thermal Equilibrium” * Changes in temperature * The boiling point of water is 100°C.

* The boiling point of water changes with altitude, because

there is less pressure at higher altitudes, bubbles in the water

vapor need less energy to escape from a liquid.

3000 meters

Water boils at 89°C

Water boils at 100°C

Less Pressure

More Pressure

Sea Level

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and Thermal Equilibrium” * Changes in temperature * Condensation occurs when a gas turns into a liquid. * Condensation, like evaporation occurs at a wide range of temperatures. * Particles in gas move more slowly near a cool surface and may form a liquid at the cooler surface. * Most gases condense when its temperature is reduced below the substances boiling point. * Sublimation occurs when a solid turns directly into a gas without going through a liquid phase. * Dry ice, which is frozen Carbon dioxide (CO2), turns directly into carbon dioxide gas under normal temperature conditions. * Deposition occurs when a gas turns directly into a solid without going through a liquid phase.


and Thermal Equilibrium” * Changes in temperature GAS.

LIQUID.

SOLID

.Meltin

g

.Fre

ezin

g

Freezing /

Melting

point

Eva

po

ratio

n

Con

de

nsa

tio

n

Boiling

point

.Su

blim

atio

n

Dep

ositio

n

* Boiling is another way of changing a liquid

into a gas.

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and Thermal Equilibrium” * Changes in temperature * The temperature scales most widely used today are the Fahrenheit, Celsius, and Kelvin scales * Celsius and Fahrenheit temperature measurements can be converted to each other using this equation: * TF = 1.8 TC + 32° * Temperature in Fahrenheit = 1.8 * temperature in Celsius + 32° * The number 32.0 indicates the difference between the ice point value in each scale: 0.0ºC and 32.0ºF * TC = (TF – 32°) / 1.8 * Temperature in Celsius = (temperature in Fahrenheit – 32°) / 1.8



* Temperature values in the Celsius and

Fahrenheit scales can have positive, negative,

or zero values

* But because the kinetic energy of the atoms

in a substance must be positive, the absolute

temperature that is proportional to that energy

should be positive also.

* A temperature scale with only positive values

is suggested by the graph on the next slide. This

scale is called the Kelvin scale.

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* A temperature difference of one degree is the

same on the Celsius and Kelvin scales. The two

scales differ only in the choice of zero point.

* Thus, the ice point (0°C) equals 273K, and the

steam point (100°C) equals 373K.

* The Celsius temperature can therefore be

converted to the Kelvin temperature by adding

273.

* TK = TC + 273

* Temperature in Kelvin = Temperature in Celsius

+ 273


and Thermal Equilibrium” * Temperature is a measure of the average kinetic energy

of the particles that make up an object.

* Heat is a flow of energy from an object at a higher

temperature to an object at a lower temperature.

* Heat and temperature are not the same thing.

* Heat and Thermal Energy

* Heat is always the transfer of energy from an object at a

higher temperature to an object of lower temperature.

* Example:

* Ice cubes temp. 0°C

* Bowl temp. 22°C

* In time ice will melt

and the water and the

bowl will have the same

temperature.

* Water and bowl temp 15°C

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and Thermal Equilibrium” * Heat and Thermal Energy

* The water and the bowl end up with the same

temperature, which is lower than the original

temperature of the bowl, but higher than the

original temperature of the ice.

* The bowl and the water end up with the same

temperature because the particles of the bowl

and the ice collide among them, gaining or

losing energy.

* When the energy flows from one object to

another, the thermal energy of both objects

changes.


and Thermal Equilibrium” * Heat and Thermal Energy

* Thermal energy is the total random kinetic

energy of particles in an object.

* Thermal energy isn’t the same as temperature

because the total amount of particles in the

object’s isn’t the same.

* Example:

* Glass of water temp 22°C

* Lake Superior temp 22°C

* More

particles

of water

* More

Thermal

energy

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and Thermal Equilibrium” * Measuring HEAT

* The most common units for measuring heat

are:

* Calorie

* Joule

* One calorie is the amount of energy needed

to raise the temperature of 1 gram of water by

1 degree Celsius.

* Joule is the standard scientific unit in which

heat is measured.

* One calorie is equal to 4.18 Joules.

1 calorie = 4.18 Joules

* In Nutrition Calorie is written with a CAPITAL C,

which is actually known as 1 kilocalorie or 1,000

calories.


and Thermal Equilibrium” * SPECIFIC HEAT

* The Specific heat of a substance is the

amount of energy required to raise the

temperature of 1 gram of the substance by 1

degree Celsius.

* Every substance has its own Specific Heat

* The Specific Heat of water is one calorie per gram per ° Celsius, and since one calorie is

equal to 4.18 Joules then we can say that the

Specific heat of water is 4.18 Joules per gram °C.

.

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and Thermal Equilibrium” * SPECIFIC HEAT

* A large value of Specific heat means that the

substance must absorb a big amount of energy

for it to increase its temperature; and it also

means that it must release a big amount of

energy to decrease it temperature.

* The high Specific Heat of water is the reason

why it is used as a coolant in car radiators.


and Thermal Equilibrium” * SPECIFIC HEAT and MASS * Thermal energy is the total random kinetic energy an object has, so it depends on the objects mass.

* Cup of water temp 90°C

* Example:

* Bath tub with water temp 40°C

* More mass = more thermal energy

* The water in the cup will cool faster because

it has less mass even though it’s hotter than the water in the tub. It will take longer for the tub water to cool because it has more mass.

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and Thermal Equilibrium” * Heat is transfer of energy from an object at a

higher temperature to an object at a lower

temperature.

* Energy moves heat in three ways:

* conduction

* convection

* radiation

* To control energy we must control

conduction, convection, and radiation.


and Thermal Equilibrium” * CONDUCTION

* Conduction is the process by which energy

moves from one object to another when they are

physically touching.

* For conduction to occur:.

1) Objects must be touching

2) Objects must have different temperatures

* Conduction will happen until the objects are:

1) Not touching

2) Have the same temperature.

* Some materials are better then others to transfer

energy (heat).

* Conductors→ are materials that transfer energy

(heat) easily.

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* Some materials are better then others to

transfer energy (heat).

* Conductors→ are materials that transfer

energy (heat) easily.

* Conductors have:

* Low values of Specific heat

* Examples: most metals

* Insulators→ are materials that do NOT transfer

energy (heat) easily.

* Insulators have:

* High values of Specific heat

* Examples: wood and plastic.



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and Thermal Equilibrium” * CONVECTION * Convection is the process that transfers

energy by the movement of large numbers of

particles in the same direction within liquids and

gases.

* With an increase in energy there is an increase

in kinetic energy, particles spread out (thermal

expansion). When particles spread out they

reduce their density. When the density is

reduced a substance goes up.


and Thermal Equilibrium” * CONVECTION

1) Warmer less dense air is

pushed up by the cooler

denser air.

2) As the air cools, it

becomes more dense

and starts to sink. 3) Sinking air moves under

the warmer air, pushing it

back up so that the cycle

repeats. * Convection in large bodies of water (lakes

and oceans) influence the temperature of

the nearby land.

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and Thermal Equilibrium” * CONVECTION


and Thermal Equilibrium” * RADIATION * Radiation is the energy that travels as

electromagnetic waves..

* Radiation includes:

* microwaves

* Infrared light

* Visible light

* The sun is the most significant source of

radiation, but all objects emit radiation and

release energy.

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and Thermal Equilibrium” * RADIATION

* Radiation from the sun

* Transfer to objects and

persons

* Objects become warmer.

* Particles move faster.

* Thermal

expansion occurs


and Thermal Equilibrium” * CONDUCTION CONVECTION & RADIATION

* Similarities → transfer energy (heat) from warmer

objects to cooler objects.

* Differences → Radiation travels through empty

space.

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and Thermal Equilibrium” * Different materials are used to control the

transfer of energy.

* Energy is always being transferred between

objects that coexist at different temperatures.

* Insulators are used to control the flow of energy

(heat) because they are poor conductors.

* Insulators are the materials that keep cool things

cool and hot things hot.

* An insulators is an energy trapper, it prevents

energy from flowing.

* Good insulators include: * Wood * Plastic

* Fiber glass * air

* Shinny materials that

reflect radiation

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Chapter 9.1 “Temperature and Thermal Equilibrium”territorio.s3-website-us-east-1.amazonaws.com/archivos/clases/... · Chapter 9.1 “Temperature and Thermal Equilibrium ... *