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Energy. Energy is defined as the ability to do work. Work = force x distance. Energy. The ability to do work. Work - cause a change or move an object. Many types- all can be changed into the other. Types of energy. Potential - stored energy Position, condition or composition

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Energy

Energy

Energy is defined as the ability to do work.

Work = force x distance


Energy1

Energy

The ability to do work.

  • Work - cause a change or move an object.

  • Many types- all can be changed into the other.


Types of energy

Types of energy

  • Potential- stored energy

    • Position, condition or composition

  • Kinetic Energy- energy something has because its moving

  • Heat- the energy that moves because of a temperature difference.

  • Chemical energy- energy released or absorbed in a chemical change.

  • Electrical energy - energy of moving charges


Types of energy con t

Types of Energy con’t

  • Radiant Energy- energy that can travel through empty space (light, UV, infrared, radio)

  • Nuclear Energy – Energy from changing the nucleus of atoms

    *All types of energy can be converted into others.

    • If you trace the source far enough back, you will end up at nuclear energy.


Conservation of energy

Conservation of Energy

Energy can be neither created or destroyed in ordinary changes (not nuclear), it can only change form.

  • Discovered by Julius Robert Mayer in 1842

  • Now called: The First Law of Thermodynamics

Law of Conservation of Mass - Energy

The total amount of mass and energy in the universe is constant.


The kinetic molecular theory is useful in describing thermal energy heat and temperature

The kinetic molecular theory is useful in describing thermal energy, heat, and temperature.

  • Some theories are based on supporting postulates.

  • A postulate is a statement which is agreed on by consensus among scientists.

  • The following are important postulates of the kinetic molecular theory:


Energy

  • All matter consists of atoms.

  • Atoms may join together to form molecules.

  • Solids usually maintain both their shape and their volume.

  • Liquids maintain their volume, but not their shape.

  • Gases do not maintain shape or volume. They will expand to fill a container of any size.

  • Molecular motion is random.

  • Molecular motion is greatest in gases, less in liquids, and least in solids.

  • Collisions between atoms and molecules transfers energy between them.

  • Molecules in motion possess kinetic energy.

  • Molecules in gases do not exert large forces on one another, unless they are colliding.

  • Also see chapter 11 of textbook

Kinetic Molecular Theory


Energy

  • Thermal energyis the average of the potential and kinetic energies possessed by atoms and molecules experiencing random motion.

  • Heat is transferred by convection, conduction, or radiation. (review the definitions of these words)

  • Heat is the thermal energy transferred from one object to another due to differences in temperature. Heat flow from high to low temperature.


Energy

  • There is no direct method used to measure heat. Indirect methods must be used.

    Temperature is a measure of the average kinetic energy of the molecules of a substance.

  • There is a direct relationship between temperature and avg. kinetic energy!

  • Temperature can be measured with a thermometer.


Energy

  • One way a thermometer can be calibrated is by the amount of thermal expansion and contraction that occurs within a given type of substance.

  • Thermometers are limited by the physical properties of the substance from which they are made. (i.e., An alcohol thermometer is of little use above the boiling point of alcohol, and a mercury thermometer will not be of any use below the freezing point of mercury.)


What s the difference between the fahrenheit and celsius temperature scales

What's the difference between the Fahrenheit and Celsius temperature scales?

  • Both scales are based on the freezing conditions of water, a very common and available liquid.

  • Since water freezes and boils at temperatures that are rather easy to generate (even before modern refrigeration), it is the most likely substance on which to base a temperature scale.


Energy

100ºC = 212ºF

0ºC = 32ºF

100ºC

212ºF

32ºF

0ºC


Energy

  • Zero Fahrenheit was the coldest temperature that the German-born scientist Gabriel Daniel Fahrenheit could create with a mixture of ice and ordinary salt.

  • He invented the mercury thermometer and introduced it and his scale in 1714 in Holland, where he lived most of his life.


Energy

  • Anders Celsius, a Swedish astronomer, introduced his scale is 1742.

    • For it, he used the freezing point of water as zero and the boiling point as 100.

  • For a long time, the Celsius scale was called "centigrade."

    • The Greek prefix "centi" means one-hundredth and each degree Celsius is one-hundredth of the way between the temperatures of freezing and boiling for water.

  • The Celsius temperature scale is part of the "metric system" of measurement (SI) and is used throughout the world, though not yet embraced by the American public.


  • Energy

    How much it changes

    100ºC = 212ºF

    0ºC = 32ºF

    100ºC = 180ºF

    0ºC

    100ºC

    212ºF

    32ºF


    Energy

    How much it changes

    100ºC = 212ºF

    0ºC = 32ºF

    100ºC = 180ºF

    1ºC = (180/100)ºF

    1ºC = 9/5ºF

    0ºC

    100ºC

    212ºF

    32ºF


    Energy

    • Scientists use a third scale, called the "absolute" or Kelvin scale.

    • This scale was invented by William Thomson, Lord Kelvin, a British scientist who made important discoveries about heat in the 1800's.

    • Scientists have determined that the coldest it can get (theoretically) is minus 273.15 degrees Celsius.

    • This temperature has never actually been reached, though scientists have come close. The value, minus 273.15 degrees Celsius, is called "absolute zero".

    • At this temperature scientists believe that molecular motion would stop. You can't get any colder than that.

    • The Kelvin scale uses this number as zero. To get other temperatures in the Kelvin scale, you add 273 degrees to the Celsius temperature.


    Energy

    The important idea is that temperature is really a measure

    of something, the average motion (kinetic energy,

    KE) of the molecules.

    KE = ½ mv2

    • Does 0°C really mean 0 KE? nope... it simply means the

      freezing point of water, a convenient standard.

    • We have to cool things down to –273.15°C before we reach

      0 KE. This is called 0 Kelvin (0 K, note: NO ° symbol.)

    • For phenomena that are proportional to the KE of the

      particles (pressure of a gas, etc.) you must use

      temperatures in K.


    Temperature conversion

    Temperature Conversion

    • K = °C + 273

    • °C = K – 273

    • °F = 9/5 °C + 32

    • °C = 5/9 (°F – 32)

    Note: In Kelvin notation, the degree sign is omitted: 283K


    Energy

    Celsius to Fahrenheit:

    *A mental shortcut for a rough estimate:

    ·Double the temperature given in Celsius

    · Add 30 to the result to find the approximate temperature in Fahrenheit.


    Energy

    Celsius Temperature to Fahrenheit

    More Celsius to Fahrenheit

    Fahrenheit to Celsius

    More Fahrenheit to Celsius


    Energy

    Fahrenheit to Celsius:

    *A mental shortcut for a rough estimate:

    ·Subtract 30 from the temperature given in Fahrenheit

    · Take half of the result to find the approximate temperature in Celsius.


    Energy

    Celsius Temperature to Fahrenheit

    More Celsius to Fahrenheit

    Fahrenheit to Celsius

    More Fahrenheit to Celsius


    How do we measure energy

    How Do We Measure Energy?

    Energy is measured in many ways.

    BTU

    • One of the basic measuring blocks is called a Btu. This stands for British thermal unit and was invented by the English.

    • Btu is the amount of heat energy it takes to raise the temperature of one pound of water by one degree Fahrenheit, at sea level.

      • One Btu equals about one blue-tip kitchen match.

      • One thousand Btus roughly equals: One average candy bar or 4/5 of a peanut butter and jelly sandwich.

      • It takes about 2,000 Btus to make a pot of coffee.


    Calorie

    Calorie

    • A calorie is a unit of measurement for energy.

    • Calorie is a French word derived from the Latin word: calor (heat).

      Modern definitions for calorie fall into two classes:

    • The small calorie or gram calorie approximates the energy needed to increase the temperature of 1 gram of water by 1 °C. This is about 4.184 joules.

    • The large calorie or kilogram calorie approximates the energy needed to increase the temperature of 1 kg of water by 1 °C. This is about 4.184 kJ, and exactly 1000 small calories.

    • 1 cal = 4.184 J


    Joule

    Joule

    • Energy also can be measured in joules. (Joules sounds exactly like the word jewels, as in diamonds and emeralds.)

    • A thousand joules is equal to a British thermal unit.

    • 1,000 joules = 1 Btu

    • So, it would take 2 million joules to make a pot of coffee.


    Energy

    • The term "joule" is named after an English scientist James Prescott Joule who lived from 1818 to 1889.

    • He discovered that heat is a type of energy.

    • One joule is the amount of energy needed to lift something weighing one pound to a height of nine inches.

    • Around the world, scientists measure energy in j.


    Energy

    • Like in the metric system, you can have kilojoules -- "kilo" means 1,000.

    • 1,000 joules = 1 kilojoule = 1 Btu

    • 1 cal = 4.184 J


    Kinetic energy and temperature

    Kinetic Energy and Temperature

    • Temperature is a measure of the Average kinetic energy of the molecules of a substance.

    • Higher temperature faster molecules.

    • At absolute zero (0 K) all molecular motion would stop.


    Energy

    High temp.

    % of Molecules

    Low temp.

    • Kinetic Energy


    Energy

    High temp.

    % of Molecules

    Low temp.

    Average kinetic energies are temperatures

    • Kinetic Energy


    Temperature

    Temperature

    • The average kinetic energy is directly proportional to the temperature in Kelvin

    • If you double the temperature (in Kelvin) you double the average kinetic energy.

    • If you change the temperature from 300 K to 600 K the kinetic energy doubles.


    Temperature1

    Temperature

    • If you change the temperature from 300ºC to 600ºC the Kinetic energy doesn’t double.

    • 873 K is not twice 573 K


    Phase changes

    Melting

    Vaporization

    Freezing

    Condensation

    Phase Changes

    Solid

    Gas

    Liquid


    Energy

    Sublimation

    Vaporization

    Deposition

    endothermic

    Melting

    Solid

    Gas

    Liquid

    Freezing

    Condensation

    exothermic


    Energy

    Heating Curve for Water

    120

    Steam

    Water and Steam

    100

    80

    60

    Water

    40

    20

    Water

    and Ice

    0

    Ice

    -20

    40

    120

    0

    220

    760

    800


    Energy

    Heating Curve for Water

    120

    Steam

    Water and Steam

    100

    80

    60

    Water

    40

    20

    Water

    and Ice

    0

    Ice

    -20

    40

    120

    0

    220

    760

    800

    gas

    liquid

    Slope = Specific Heat

    Solid


    Energy

    Heating Curve for Water

    120

    Steam

    Water and Steam

    100

    80

    60

    Water

    40

    20

    Water

    and Ice

    0

    Ice

    -20

    40

    120

    0

    220

    760

    800

    Both Solid and liquid


    Energy

    Heating Curve for Water

    120

    Steam

    Water and Steam

    100

    80

    60

    Water

    40

    20

    Water

    and Ice

    0

    Ice

    -20

    40

    120

    0

    220

    760

    800

    Both liquid and gas


    Energy

    Heating Curve for Water

    120

    Steam

    Water and Steam

    100

    80

    60

    Water

    40

    20

    Water

    and Ice

    0

    Ice

    -20

    40

    120

    0

    220

    760

    800

    Heat of Vaporization


    Energy

    Heating Curve for Water

    120

    Steam

    Water and Steam

    100

    80

    60

    Water

    40

    20

    Water

    and Ice

    0

    Ice

    -20

    40

    120

    0

    220

    760

    800

    Heat of Fusion


    Energy

    Heating Curve for Water

    120

    Steam

    Water and Steam

    100

    80

    60

    Water

    40

    20

    Water

    and Ice

    0

    Ice

    -20

    40

    120

    0

    220

    760

    800

    Plateau = phase equilibrium


    Energy and phase changes

    Energy and phase changes


    Heat is transferred to different materials at different rates

    Heat is transferred to different materials at different rates.

    • The specific heat capacity (C) determines the rate at which heat will be absorbed.

    • Even though mass is present in the formula it is an intensive property like density and is unique for each substance.

    • The specific heat capacity for water is 4.18J/g

    • The quantity of heat absorbed (Q) can be calculated by: Q=mCT

      m=mass T=change in temperature


    Heat capacity

    Heat Capacity

    Heat capacity is an extensive property, meaning it depends on the mass of the object.

    Ex: 1000g of water can hold more heat than 10 g of water.


    Calculating energy

    Calculating Energy

    Q means heat energy lost or gained.

    Law of Conservation of Mass-Energy

    m= mass of substance; Cp= specific heat capacity; DT = change in temperature

    Qlost = Qgained

    Three equations:

    • Q= mass x Cp x DT

    • Q= Hf x mass

    • Q= Hv x mass


    Energy

    Heating Curve for Water

    120

    Steam

    Water and Steam

    100

    80

    60

    Water

    40

    20

    Water

    and Ice

    0

    Ice

    -20

    40

    120

    0

    220

    760

    800


    Energy and phase change

    Energy and Phase Change

    • Heat of fusion energy required to change one gram of a substance from solid to liquid. (endothermic rxn)

    • Heat of solidification energy released when one gram of a substance changes from liquid to solid. (exothermic rxn)

    • For water 80 cal/g or 334 J/g


    Energy and phase change1

    Energy and Phase Change

    • Heat of vaporization energy required to change one gram of a substance from liquid to gas. (endothermic rxn)

    • Heat of condensation energy released when one gram of a substance changes from gas to liquid. (exothermic rxn)

    • For water 540 cal/g or 2260 J/g


    Energy

    Three equations:

    Q= mass x Cp x DT

    (used at slopes)

    Q= Hf x mass (used at s/l equilibria)

    Q= Hv x mass (used at l/g equilibria)


    Energy

    Heating Curve for Water

    120

    Steam

    Water and Steam

    100

    80

    60

    Water

    40

    20

    Water

    and Ice

    0

    Ice

    -20

    40

    120

    0

    220

    760

    800


    Regents question 06 02 28

    Regents Question: 06/02 #28

    As ice melts at standard pressure, its temperature remains at 0°C until it has completely melted. Its potential energy

    (1) decreases

    (2) increases

    (3) remains the same

    þ


    Regents question 08 02 54

    Gas Only

    Phase change

    Liquid Only

    Regents Question: 08/02 #54

    A sample of water is heated from a liquid at 40°C to a gas at 110°C. The graph of the heating curve is shown in your answer booklet.

    a On the heating curve diagram provided in your answer booklet, label each of the following regions:

    Liquid, onlyGas, onlyPhase change


    Regents question cont d

    Regents Question: cont’d

    b For section QR of the graph, state what is happening to the water molecules as heat is added.

    c For section RS of the graph, state what is happening to the water molecules as heat is added.

    They move faster, their temperature increases.

    Their intermolecular bonds are breaking, their potential energy is increasing.


    Regents question 01 02 47

    Regents Question: 01/02 #47

    What is the melting point of this substance?

    (1) 30°C(3) 90°C

    (2) 55°C (4) 120°C

    þ


    Energy

    The quantity of energy absorbed or released during a phase change can be calculated using the Heat of Fusion or Heat of Vaporization

    • Melting (fusion) or freezing (solidification)

      • Q=mHf where Hfis the heat of fusion

        (for water: 333.6 J/g)

    • Boiling (vaporization) or condensing

      • Q=mHv where Hvis the heat of vaporization

        (for water: 2259 J/g)

    HfandHv are given to Table B – m is the mass


    Regents question 08 02 24

    Regents Question: 08/02 #24

    In which equation does the term “heat” represent heat of fusion?

    (1) NaCl(s) + heat  NaCl(l)

    (2) NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l)+ heat

    (3) H2O(l)+ heat  H2O(g)

    (4) H2O(l)+ HCl(g) H3O+(aq) + Cl –(aq) + heat

    þ

    Fusion refers to melting.


    Melting point

    Melting Point

    • The temperature at which a liquid and a solid are in equilibrium

    • The melting point for ice is 0ºC

    • The melting point of a substance is the same as its freezing point


    Regents question 08 02 18

    Regents Question: 08/02 #18

    The solid and liquid phases of water can exist in a state of equilibrium at 1 atmosphere of pressure and a temperature of

    (1) 0°C (3) 273°C

    (2) 100°C(4) 373°C

    þ


    To calculate q from ice gas

    To calculate Q from ice  gas

    The total heat = the sum of all the heats you have to use

    • Go in order

    Heat Water

    Boil Water

    Heat Steam

    Heat

    Ice

    Melt Ice

    +

    +

    +

    +

    Below 0°C

    0°C -

    100°C

    At

    100°C

    Above

    100°C

    At

    0°C


    Energy

    Heating Curve for Water

    120

    Steam

    Water and Steam

    100

    80

    60

    Water

    40

    20

    Water

    and Ice

    0

    Ice

    -20

    40

    120

    0

    220

    760

    800

    Q

    Q

    +

    +

    Q

    +

    Q

    +

    Q


    Energy

    Heating Curve for Water

    120

    Steam

    Water and Steam

    100

    80

    60

    Water

    40

    20

    Water

    and Ice

    0

    Ice

    -20

    40

    120

    0

    220

    760

    800

    Q=m x Cp x ∆T

    Q= Hv x m

    Q=m x Cp x ∆T

    Q= Hf x m

    Q=m x Cp x ∆T


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