Chapter Four - Energy from Combustion Flashcards Preview

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

What is work?

movement of an object over a distance

2

What is heat?

energy that goes from hot --> cold

3

What is temperature?

amount of heat energy in an object
-determines direction of heat flow
-measurement of molecular motion
-more motion = higher temp

4

How do heat and temp relate?

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

5

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

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

6

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

-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

What are the units of energy?

1. Joule (J)
2. Calorie (cal)

8

What is a Joule?

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

9

What is a calorie?

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

What are Thermodynamics?

how heat moves

11

What is the first law of thermodynamics?

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

12

What forms can energy take?

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

What is efficiency?

how much heat it takes to do work
-never 100% transferred in real world because some heat loss always occurs

14

What is Potential energy?

how much energy you can get from a system

15

What is Kinetic energy?

energy of motion

16

What is Thermal energy?

heat, sound waves

17

What is the second law of thermodynamics?

heat ---(transferred into)---> work with 100% efficiency = impossible!!!
-heat won't flow cold--> hot (takes energy)
-entropy (randomness) increases, energy/heat will disperse

18

What are good energy sources? bad?

good: wood, oil, and coal
bad: dirt

19

What is combustion?

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

What does Methane combustion look like?

CH4 + 2CO2 --> CO2 + 2H2O + heat
-exothermic reaction = gives off heat/energy

21

What is the heat of combustion?

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

When bonds are broken, energy is ______

absorbed

23

When bonds are formed, energy is ______

released

24

What is bond energy?

the amount of energy needed to break a specific bond
-depends on the atoms that are sharing electrons

25

What is an endothermic reaction?

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

26

What defines a good fuel?

-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

What is the transition state?

bonds half formed/half broken

28

What is activation energy?

the energy that breaks the bonds, kicks the reaction off

29

What are useful reactions?

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

30

How can you increase the rate of reaction between reactants?

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

Coal

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

What are the advantages of coal?

-large supply
-widely used
-more efficient than wood
-doesn't need processing (just burn)

33

What are the drawbacks of coal?

-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

Petroleum

"Petroleum is King"
-decomposed sugars
-liquid (pumped through pipelines)
-40-60% more energy/gram than coal
-mix of hydrocarbons

35

What are hydrocarbons?

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

36

MEPB

"mother eats peanut butter"
Methane, Ethane, Propane, Butane

37

Gasoline

-automobile fuel (gas = $$$)
-US demand (900 million gallons a day)

38

Drawback of petroleum

-must be refined

39

Natural Gases

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