Energy (Ch. 10) - PowerPoint PPT Presentation

Loading...

PPT – Energy (Ch. 10) PowerPoint presentation | free to download - id: 704865-NWUzZ



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Energy (Ch. 10)

Description:

Energy (Ch. 10) – PowerPoint PPT presentation

Number of Views:65
Avg rating:3.0/5.0
Slides: 30
Provided by: setu74
Learn more at: http://aischemistry.pbworks.com
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Energy (Ch. 10)


1
Energy(Ch. 10)
2
What is Energy?
10.1 Energy, Temperature and Heat
  • Energy is the ability of something to do work or
    make heat.

3
Forms of Energy
  • Heat
  • Light
  • Sound
  • Motion
  • Electrical

4
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

5
Work
  • When you ride your bicycle down the hill, gravity
    does work on you.
  • Work is a force pushing or pulling on something
    over distance.

6
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
    happened).
  • Speed is NOT a state function, because it depends
    on

7
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.

8
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.

9
Exothermic Vs. Endothermic
  • The system is the thing we are interested in.
  • The surroundings are everything else in the
    world.
  • 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)

10
Exothermic Vs. Endothermic
  • Exothermic energy being released
  • Endothermic energy being absorbed

11
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

12
How this looks on a graph
Energy released to the surroundings
13
Does this Graph Represent an Exothermic or
Endothermic Reaction?
  • Exo or Endo?
  • Exothermic, because molecules have less energy
    then when they started

14
Does this Graph Represent an Exothermic or
Endothermic Reaction?
  • Exo or Endo?
  • Endothermic, because molecules have more energy
    then when they started

15
10.2 The Flow of Energy
16
Thermodynamics
  • 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

17
Measuring Energy Changes
  • You can measure heat in joules (J) or calories
    (cal)
  • One calorie energy needed to raise the
    temperature of one gram of water one degree
    Celsius.
  • 1 cal 4.184 J
  • Practice Convert 44.2 cal to J

18
Thermodynamic quantities
  • Thermodynamic quantities (q, w and ? E) have two
    parts
  • Number the size of the change
  • Sign ( or )shows the direction of the flow.

19
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)

20
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.

21
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?

22
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
    methane?

23
  • An exothermic reaction has a negative (-)
    enthalpy.
  • 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

24
Calorimeter
  • A calorimeter is a device used to measure the
    heat in a chemical reaction.

25
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 ???

26
  • 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
    backwards
  • 2NO O2 ? 2NO2 ?H -112 kJ

27
  • 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

28
10.4 Using Energy in the Real World
  • Read p339-349 and answer questions 1-7 on p350
  • Go to this websites
  • http//www.adventuresinenergy.org/ - What are
    Oil and Natural Gas? and Refining
    Distillation
  • http//science.howstuffworks.com/oil-refining4.htm
  • And answer the questions on the worksheet,
    Petroleum Assignment

29
(No Transcript)
About PowerShow.com