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Energy (Ch. 10)


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Title: Energy (Ch. 10)

Energy(Ch. 10)
What is Energy?
10.1 Energy, Temperature and Heat
  • Energy is the ability of something to do work or
    make heat.

Forms of Energy
  • Heat
  • Light
  • Sound
  • Motion
  • Electrical

Energy Change
  • The Law of Conservation of Energy Energy cannot
    be made or destroyed, but it can change from one
    type to another type (of energy).
  • If you ride a bicycle down a hill, you move
    faster and faster. When the hill ends, you slow
    down and stop. Why?
  • You slow down because friction of the tires on
    the road changed your energy to heat.
  • The energy change Motion ? Heat

  • When you ride your bicycle down the hill, gravity
    does work on you.
  • Work is a force pushing or pulling on something
    over distance.

Work Heat Energy
  • Case A You ride down a hill on your bicycle and
    go very fast.
  • Case BYour friend uses breaks, goes slow and
    stops at the bottom.
  • For both people, the energy change is the same!
  • Energy is a state function because it does not
    depend on the pathway (how the energy change
  • Speed is NOT a state function, because it depends

Temperature and Heat
  • Temperature is the measure of random motions of
    the things.
  • Heat is the movement of energy.
  • Thermal energy is the random movement of
    molecules and atoms.

Temperature and Heat
  • If you have a hot cup of coffee, after about an
    hour it will cool to be the same temperature as
    the room.
  • What happened to the molecules in the coffee and
    the air?
  • At first, the molecules in the coffee are moving
    faster than the molecules of air.
  • The coffee molecules move slower.
  • The air molecules move faster.
  • The energy moves from the coffee
  • to the air.

Exothermic Vs. Endothermic
  • The system is the thing we are interested in.
  • The surroundings are everything else in the
  • Example I want to measure the temperature change
    of my cup of coffee.
  • The system the coffee cup
  • The surroundings everything else (the air,
    chairs in the room, the students)

Exothermic Vs. Endothermic
  • Exothermic energy being released
  • Endothermic energy being absorbed

Exothermic Vs Endothermic REACTIONS
  • To determine if a chemical reaction is exothermic
    or endothermic you must look at the energy of the
    whole reaction
  • Exothermic Reaction OVERALL, the reaction
    releases more energy than it takes in
  • Endothermic Reaction OVERALL, the reaction
    absorbs more energy than it releases

How this looks on a graph
Energy released to the surroundings
Does this Graph Represent an Exothermic or
Endothermic Reaction?
  • Exo or Endo?
  • Exothermic, because molecules have less energy
    then when they started

Does this Graph Represent an Exothermic or
Endothermic Reaction?
  • Exo or Endo?
  • Endothermic, because molecules have more energy
    then when they started

10.2 The Flow of Energy
  • Thermodynamics is the study of energy
  • The first law of thermodynamics the law of
    conservation of energy the energy of the
    universe is constant.
  • Internal energy (E) energy of the system
  • ? E q w
  • ? E means the change in energy
  • q heat
  • w work

Measuring Energy Changes
  • You can measure heat in joules (J) or calories
  • One calorie energy needed to raise the
    temperature of one gram of water one degree
  • 1 cal 4.184 J
  • Practice Convert 44.2 cal to J

Thermodynamic quantities
  • Thermodynamic quantities (q, w and ? E) have two
  • Number the size of the change
  • Sign ( or )shows the direction of the flow.

Calculating Heat from lab data
  • Energy Specific heat x Mass x Temp change
  • Q sm?T
  • This equation tells us how much energy was gained
    by a substance (if it was heated) or lost by a
    substance (if it was cooled)
  • What part of this equation will tell you if
    something is heated or cooled?
  • Temp change (also written as ?T)

What is a Specific Heat?
  • Specific Heat Capacity the amount of energy
    required to heat 1 gram of something by 1C.
  • Every substance has a different specific heat
  • What is the specific heat of water
  • 4.18 J/(gC) ? memorize!
  • This number tells us that if we want to raise the
    temperature of a container of water by 1C, then
    each gram of water in the container must gain
    4.18 J of energy.

Lets do an example
  • Lets say your making some delicious Ramen
    noodles for dinner mmm..mmmm good!
  • The directions say to boil 2 cups of water (500
    grams of water)
  • If the water starts at room temp ( 20C), how
    much energy must it gain to boil?

10.3 Thermochemistry
  • Enthalpy ?H the heat for a reaction
  • The units of Enthalpy are kJ
  • Example If you burn one mole of CH4 the enthalpy
    (?H) is 890 kJ.
  • In other words
  • CH4 O2 ? CO2 H2O ?H -890 kJ
  • How much heat is released if you burn 5.8 grams

  • An exothermic reaction has a negative (-)
  • Is this reaction exothermic or endothermic?
  • CH4 O2 ? CO2 H2O ?H -890 kJ
  • Yes, exothermic
  • The reverse reaction would be endothermic and so
    it has a positive () sign
  • CO2 H2O ? CH4 O2 ?H 890 kJ

  • A calorimeter is a device used to measure the
    heat in a chemical reaction.

Hesss Law
  • Hesss Law The change in enthalpy for a reaction
    is the same whether a reaction takes place in one
    step or many steps.
  • Example What is the change in enthalpy for
  • N2 O2 ? NO2 ?H ???

  • N2 O2 ? NO2 ?H ???
  • You know
  • N2 O2 ? 2NO ?H 180 kJ
  • 2NO2 ? 2NO O2 ?H 112 kJ
  • Can we make NO2 from N2 and O2 in two steps?
  • Yes, butyou have to do the second reaction
  • 2NO O2 ? 2NO2 ?H -112 kJ

  • If we add these two reactions, we can find the ?H
    of N2 O2 ? NO2
  • N2 O2 ? 2NO ?H 180 kJ
  • 2NO O2 ? 2NO2 ?H -112 kJ
  • N2 O2 ? NO2 ?H 180 (-112) 68 kJ

10.4 Using Energy in the Real World
  • Read p339-349 and answer questions 1-7 on p350
  • Go to this websites
  • http// - What are
    Oil and Natural Gas? and Refining
  • http//
  • And answer the questions on the worksheet,
    Petroleum Assignment

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