Chapter Four - Energy from Combustion

Question 1

What is work?

Answer 1

movement of an object over a distance

Question 2

What is heat?

Answer 2

energy that goes from hot –> cold

Question 3

What is temperature?

Answer 3

amount of heat energy in an object

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

Question 4

How do heat and temp relate?

Answer 4

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

Question 5

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

Answer 5

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

Question 6

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

depends on…

Answer 6

• 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

Question 7

What are the units of energy?

Answer 7

1. Joule (J)

2. Calorie (cal)

Question 8

What is a Joule?

Answer 8

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

Question 9

What is a calorie?

Answer 9

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)

Question 10

What are Thermodynamics?

Answer 10

how heat moves

Question 11

What is the first law of thermodynamics?

Answer 11

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

Question 12

What forms can energy take?

Answer 12

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

Question 13

What is efficiency?

Answer 13

how much heat it takes to do work

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

Question 14

What is Potential energy?

Answer 14

how much energy you can get from a system

Question 15

What is Kinetic energy?

Answer 15

energy of motion

Question 16

What is Thermal energy?

Answer 16

heat, sound waves

Question 17

What is the second law of thermodynamics?

Answer 17

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

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

Question 18

What are good energy sources? bad?

Answer 18

good: wood, oil, and coal
bad: dirt

Question 19

What is combustion?

Answer 19

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

Question 20

What does Methane combustion look like?

Answer 20

CH4 + 2CO2 –> CO2 + 2H2O + heat

-exothermic reaction = gives off heat/energy

Question 21

What is the heat of combustion?

Answer 21

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)

Question 22

When bonds are broken, energy is ______

Answer 22

absorbed

Question 23

When bonds are formed, energy is ______

Answer 23

released

Question 24

What is bond energy?

Answer 24

the amount of energy needed to break a specific bond

-depends on the atoms that are sharing electrons

Question 25

What is an endothermic reaction?

Answer 25

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

Question 26

What defines a good fuel?

Answer 26

- 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)

Question 27

What is the transition state?

Answer 27

bonds half formed/half broken

Question 28

What is activation energy?

Answer 28

the energy that breaks the bonds, kicks the reaction off

Question 29

What are useful reactions?

Answer 29

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

Question 30

How can you increase the rate of reaction between reactants?

Answer 30

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

Question 31

Coal

Answer 31

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%

Question 32

What are the advantages of coal?

Answer 32

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

Question 33

What are the drawbacks of coal?

Answer 33

- 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

Question 34

Petroleum

Answer 34

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

Question 35

What are hydrocarbons?

Answer 35

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

Question 36

MEPB

Answer 36

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

Question 37

Gasoline

Answer 37

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

Question 38

Drawback of petroleum

Answer 38

-must be refined

Question 39

Natural Gases

Answer 39

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