Ch. 15- Energy Flashcards
photosynthesis
the chemical process used by green plants to convert solar energy into chemical energy by reducing carbon dioxide and producing glucose and oxygen
our biosphere receives about 1 billionth of the sun’s energy output… where does that fraction of energy go?
- 30% is immediately reflected back into space as UV & visible light
- ~50% is converted to heat for a habitable planet
- ~23% powers the water cycle
- <0.02% is absorbed by green plants
what needs to be present for photosynthesis to occur?
chlorophyll & enzymes
what are the various energy units and when do we use them?
- Calories or kcals (energy content of food)
- joules (amount of energy in SI units)
- watts (amount of power/the rate at which energy is used in SI units
- kilowatt hour (the amount of energy consumed by a 1 kW device in 1 h)
how many cal are in 1 kcal?
1000 cal
how many kJ are in 1000 J?
1 kJ
how many J are in 1 cal?
4.18 J
how many W are in 1 J/s?
1 W
how many W are in 1 kW?
1000 W
how many kJ are in 1 kWh?
3600 kJ
how many s are in 1 h?
3600 s
potential energy
energy due to position or composition
kinetic energy
the energy of motion
kinetic energy
the energy of motion
system
the part of the universe under consideration in a thermochemical study
surroundings
everything that is not part of the system being observed in a thermochemical study
exothermic
describes a process that releases heat to the surroundings
enthalpy of reaction (heat of reaction)
the amount of energy released or absorbed in a reaction with stoichiometric amounts of each reactant
endothermic
describes a process that requires heat to occur, taking that energy from the surroundings
equation for determining if a chemical process is endothermic or exothermic
enthalpy change = (the sum of energy needed to break all the bonds) - (the sum of energy released in forming bonds)
- *if enthalpy change is a negative number, its exothermic
- *if enthalpy change is a positive number, its endothermic
equation for determining if a chemical process is endothermic or exothermic
enthalpy change = (the sum of energy needed to break all the bonds) - (the sum of energy released in forming bonds)
- *if enthalpy change is a negative number, its exothermic
- *if enthalpy change is a positive number, its endothermic
chemical kinetics
the study of reaction rates and factors that affect those rates (temperature, solute concentration, presence of a catalyst, etc.)
chemical kinetics
the study of reaction rates and factors that affect those rates (temperature, solute concentration, presence of a catalyst, etc.)
how does temperature affect the rate of a chemical reaction?
the higher the temperature, the faster the reaction occurs because the molecules move faster & collide more frequently, increasing chances of reaction
how does temperature affect the rate of a chemical reaction?
the higher the concentration, the faster the reaction occurs the because when we crowd molecules into a given volume of space, the molecules collide more often, increasing chances of reaction
how do catalysts affect the rate of a chemical reaction?
certain catalysts can be used to speed up the chemical reaction by lowering the reaction’s activation energy (amount of energy needed to initiate the reaction)
first law of thermodynamics (law of conservation of energy)
states that energy cannot be created or destroyed, only transformed from one form to another
facts about energy that do not support the 1st law of thermodynamics
- energy can be changed from one form to another
- not all forms of energy are equally useful
- more useful forms of energy are constantly being degraded into less useful forms or distributed in a way that make the energy nearly impossible to recover
second law of thermodynamics
the forms of energy available for useful work are continually decreasing; energy spontaneously tends to distribute itself among the objects in the universe
explain entropy with solids/liquids/gases
- solids have low entropy
- liquids have moderate entropy
- gases have high entropy
define microstates & explain their importance when determining entropy (this is mentioned in 15.4 in case you need to further look into it, considering you barely took notes on it)
- 1 microstate is 1 possible arrangement of molecules in a substance; almost as if you were to take a screenshot of that substance, how many possible different screenshots you could take = however many possible microstates exist (considering molecules are in constant movement)
- entropy is determined by the amount of microstates to possibly exist in a substance
fuel
a substance that burns readily with the release of significant energy, ideally in a controllable manner
fossil fuels
natural fuels, especially coal, petroleum, and natural gas, derived from once-living plants and animals
fuels vs. non-fuels
(a) fuels are reduced forms of matter than release relatively large quantities of heat when burned
(b) non-fuels are compounds that are oxidized forms of matter
which fossil fuels are likely to be depleted within the current century?
natural gas & petroleum
name the fossil fuels
coal
petroleum
natural gas
coal
a solid fossil fuel that is rich in carbon
how were today’s coal deposits formed?
- millions of years ago, Earth was warmer & plants flourished
- overtime, some plant material became buried under mud & water
- due to lack of oxygen, those plants decayed only partially, preserving much of the cellulose molecules they’re made up of
- as they became buried deeper & deeper, pressure was increased & their cellulose molecules broke down
- small molecules rich in hydrogen & oxygen escaped (mostly as water), leaving behind material increasingly rich in carbon
pros of using coal as fuel
- most plentiful fossil fuel
- can be used industrially & medically depending on how it’s burned
cons of using coal as fuel
- dangerous to obtain (coal mining = accidents & black lung disease)
- ash leftover from combustion = PM; major air pollutant (airborne mercury)
- combustion produces sulfur dioxide, coal’s primary pollutant
- coal mining destroys surrounding land
hydraulic fracturing (fracking)
a process for obtaining oil or natural gas whereby deep holes are drilled into geological formations, and high-pressured fluids (usually water mixed with fine sand) are pumped in to form cracks in the rocks through which the desired fluid may flow
natural gas
a mixture of gases, mainly methane, found in underground deposits
composition of typical natural gas
- mainly methane
- ethane
- nitrogen
- some propane
- some carbon dioxide
- tiny amounts of pentanes & butanes
how do we use natural gas?
- mainly as fuel (supplies ~23% of worldwide energy consumption)
- as raw material to create other necessary products
petroleum
a thick liquid mixture of (mostly) hydrocarbons with various impurities including sulfur, occurring in various geologic deposits
products of combusted natural gas
- mainly carbon dioxide & water
- when burned in insufficient air… carbon monoxide & soot
products of combusted petroleum
- carbon dioxide
- water vapor
fractions of typical petroleum
(in order from lowest to highest boiling points) - petroleum gas - gasoline - kerosene - heating oil - lubricating oils/greases - residues (see chart in 15.7 for more details)
octane rating
comparison of the anti-knock quality of a gasoline with that of pure isooctane, which has a rating of 100
catalytic reforming
a process that converts straight-chain alkanes to aromatic hydrocarbons
synthesis gas
a mixture of carbon monoxide and hydrogen gas used for organic synthesis
nuclear reactor
a power plant that produces electricity using nuclear fission reactions
breeder reactor
a nuclear reactor that converts nonfissionable isotopes to nuclear fuel; most commonly, uranium-238 is converted to plutonium-239 by neutron bombardment
advantages of nuclear energy
- plants do not add to the greenhouse effect
- plants do not add air pollutants to the atmosphere
- it lowers trade deficits
- way more sustainable than other forms of energy
disadvantages of nuclear energy
- elaborate/expensive safety precautions must be taken in & around plants
- fear of potential nuclear power plant meltdown
- requirement of storing & isolating highly radioactive fission products for centuries
- production of thermal pollution
explain how nuclear reactors work
fission of uranium heats the water in the reactor, which generates steam that drives the turbines, producing electricity. Control rods absorb neutrons to slow the fission reaction as needed.
photovoltaic cell (solar cell)
a cell that uses semiconductors to convert sunlight directly into electrical energy
biomass
dry plant material used as fuel
biomass
dry plant material used as fuel
geothermal energy
energy derived from the heat of Earth’s interior
fuel cell
an electrochemical cell that produces electricity directly from continuously supplied fuel and oxygen
