Chapter Four - Energy from Combustion Flashcards Preview

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Flashcards in Chapter Four - Energy from Combustion Deck (39)
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1
Q

What is work?

A

movement of an object over a distance

2
Q

What is heat?

A

energy that goes from hot –> cold

3
Q

What is temperature?

A

amount of heat energy in an object

  • determines direction of heat flow
  • measurement of molecular motion
  • more motion = higher temp
4
Q

How do heat and temp relate?

A

heat is the consequence of motion at the molecular level, temp is a measurement of an average speed of that motion

5
Q

How is coal used to create electricity in a power plant?

A
  1. Combustion
  2. Boil water in a closed high pressure system (generate steam)
  3. Turn turbine to create electricity
6
Q

Amount of heat in an object (100mL vs. 200mL of substance)

depends on…

A
  • molecules move at the same speed
  • 200mL has 2x the molecules and heat energy
  • takes 2x the energy to heat up the 200mL
  • -> depends on…. temp, mass, and material
7
Q

What are the units of energy?

A
  1. Joule (J)

2. Calorie (cal)

8
Q

What is a Joule?

A

the energy is takes to beat a heart once, or to lift 1kg by 10cm

9
Q

What is a calorie?

A

the amount of energy it takes to raise temp of 1g H2O by 1 degree C
=4.184 Joules
–> 1 Calorie = 1000 calories = 1 kilocalorie (used on food labels)

10
Q

What are Thermodynamics?

A

how heat moves

11
Q

What is the first law of thermodynamics?

A

energy is neither created nor destroyed (Law of Conservation of Energy)
–>energy sources are consumed (chem bonds)

12
Q

What forms can energy take?

A
  1. Potential Energy (chemical bonds)
    - arrangement of energy
    - molecular structure
    - fossil fuels and food (burning –> heat)
  2. Heat –> Mechanical Energy
    - steam, gasoline engines
    - can do work
  3. Mechanical Energy –> Electrical generators
    - can do work, light, heat
13
Q

What is efficiency?

A

how much heat it takes to do work

-never 100% transferred in real world because some heat loss always occurs

14
Q

What is Potential energy?

A

how much energy you can get from a system

15
Q

What is Kinetic energy?

A

energy of motion

16
Q

What is Thermal energy?

A

heat, sound waves

17
Q

What is the second law of thermodynamics?

A

heat —(transferred into)—> work with 100% efficiency = impossible!!!

  • heat won’t flow cold–> hot (takes energy)
  • entropy (randomness) increases, energy/heat will disperse
18
Q

What are good energy sources? bad?

A

good: wood, oil, and coal
bad: dirt

19
Q

What is combustion?

A

rapid combination with CO2
reactants + O2 –> products + heat
-potential energy of the reactants (reactive) must be greater than the potential energy of the products (stable) otherwise there is no reaction

20
Q

What does Methane combustion look like?

A

CH4 + 2CO2 –> CO2 + 2H2O + heat

-exothermic reaction = gives off heat/energy

21
Q

What is the heat of combustion?

A

energy given off upon combustion of a specific amount of a substance
-determined by a bomb calorimeter (when heat is released, the temp of the water inside will increase)

22
Q

When bonds are broken, energy is ______

A

absorbed

23
Q

When bonds are formed, energy is ______

A

released

24
Q

What is bond energy?

A

the amount of energy needed to break a specific bond

-depends on the atoms that are sharing electrons

25
Q

What is an endothermic reaction?

A

a reaction that requires energy to be put in, greater than what’s put off, absorbs heat

26
Q

What defines a good fuel?

A
  • large energy change (exothermic)
  • reactants: weak bonds
  • products: strong bonds
  • -> H2O and CO2 are poor fuels (O-H, C=O) it would take lots of energy to break these bonds)
27
Q

What is the transition state?

A

bonds half formed/half broken

28
Q

What is activation energy?

A

the energy that breaks the bonds, kicks the reaction off

29
Q

What are useful reactions?

A

neither too fast (too difficult to control, explosion, ex. H-bomb)
or too slow (energy release takes too long, ex. rotting wood)

30
Q

How can you increase the rate of reaction between reactants?

A
  1. Maximize surface area of reactants (ex. stirring a solution)
  2. Raise temp (add energy to the system)
  3. Catalysts (decrease activation energy without being consumed)<– doing this can strain/make bonds weaker
31
Q

Coal

A

Yields 2-3x more energy/gram than wood

  • more % carbon –> less O2 used and H2O made
  • -> coal in 85% carbon while wood is only 40%
32
Q

What are the advantages of coal?

A
  • large supply
  • widely used
  • more efficient than wood
  • doesn’t need processing (just burn)
33
Q

What are the drawbacks of coal?

A
  • difficult to get: mining (accidents, health risks) is expensive to make safe, strip mining = bad for env.
  • difficult to transport, can’t push through pipelines
34
Q

Petroleum

A

“Petroleum is King”

  • decomposed sugars
  • liquid (pumped through pipelines)
  • 40-60% more energy/gram than coal
  • mix of hydrocarbons
35
Q

What are hydrocarbons?

A

compounds of C and H (ex. methane, butane, ethane, propane)

36
Q

MEPB

A

“mother eats peanut butter”

Methane, Ethane, Propane, Butane

37
Q

Gasoline

A
  • automobile fuel (gas = $$$)

- US demand (900 million gallons a day)

38
Q

Drawback of petroleum

A

-must be refined

39
Q

Natural Gases

A
  • fossil fuels, found w/oil
  • Methane (CH4)
  • Pipelines (gas)
  • Heating
  • Low pollutant
  • less CO2 than oil/coal