Chapter Four - Energy from Combustion Flashcards
What is work?
movement of an object over a distance
What is heat?
energy that goes from hot –> cold
What is temperature?
amount of heat energy in an object
- determines direction of heat flow
- measurement of molecular motion
- more motion = higher temp
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
How is coal used to create electricity in a power plant?
- Combustion
- Boil water in a closed high pressure system (generate steam)
- Turn turbine to create electricity
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
What are the units of energy?
- Joule (J)
2. Calorie (cal)
What is a Joule?
the energy is takes to beat a heart once, or to lift 1kg by 10cm
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)
What are Thermodynamics?
how heat moves
What is the first law of thermodynamics?
energy is neither created nor destroyed (Law of Conservation of Energy)
–>energy sources are consumed (chem bonds)
What forms can energy take?
- Potential Energy (chemical bonds)
- arrangement of energy
- molecular structure
- fossil fuels and food (burning –> heat) - Heat –> Mechanical Energy
- steam, gasoline engines
- can do work - Mechanical Energy –> Electrical generators
- can do work, light, heat
What is efficiency?
how much heat it takes to do work
-never 100% transferred in real world because some heat loss always occurs
What is Potential energy?
how much energy you can get from a system
What is Kinetic energy?
energy of motion
What is Thermal energy?
heat, sound waves
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
What are good energy sources? bad?
good: wood, oil, and coal
bad: dirt
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
What does Methane combustion look like?
CH4 + 2CO2 –> CO2 + 2H2O + heat
-exothermic reaction = gives off heat/energy
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)
When bonds are broken, energy is ______
absorbed
When bonds are formed, energy is ______
released
What is bond energy?
the amount of energy needed to break a specific bond
-depends on the atoms that are sharing electrons
What is an endothermic reaction?
a reaction that requires energy to be put in, greater than what’s put off, absorbs heat
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)
What is the transition state?
bonds half formed/half broken
What is activation energy?
the energy that breaks the bonds, kicks the reaction off
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)
How can you increase the rate of reaction between reactants?
- Maximize surface area of reactants (ex. stirring a solution)
- Raise temp (add energy to the system)
- Catalysts (decrease activation energy without being consumed)<– doing this can strain/make bonds weaker
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%
What are the advantages of coal?
- large supply
- widely used
- more efficient than wood
- doesn’t need processing (just burn)
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
Petroleum
“Petroleum is King”
- decomposed sugars
- liquid (pumped through pipelines)
- 40-60% more energy/gram than coal
- mix of hydrocarbons
What are hydrocarbons?
compounds of C and H (ex. methane, butane, ethane, propane)
MEPB
“mother eats peanut butter”
Methane, Ethane, Propane, Butane
Gasoline
- automobile fuel (gas = $$$)
- US demand (900 million gallons a day)
Drawback of petroleum
-must be refined
Natural Gases
- fossil fuels, found w/oil
- Methane (CH4)
- Pipelines (gas)
- Heating
- Low pollutant
- less CO2 than oil/coal
