Ch. 3: Thermodynamics Flashcards
defn: zeroth law of thermodynamics
when one object is in thermal equilibrium with another object
and the second object is in thermal equilibrium with a third object
then the first and third object are also in thermal equilibrium
as such, when brought into thermal contact, no net heat will flow between these objects
the transitive property of thermal systems!!
what is a corollary of the zeroth law of thermodynamics?
heat flows between two objects not in thermal equilibrium
what is temperature molecularly and macroscopically?
MOLECULAR = temperature is proportional to the average kinetic energy of the particles that make up the substance
MACROSCOPIC = the difference in temperature between two objects that determines the direction of heat flow
which direction does heat move spontaneously?
from materials that have higher temperatures to materials that have lower temperatures (when possible)
defn: heat
the transfer of thermal energy from a hotter object with higher temperature (energy) to a colder object with lower temperature (energy)
defn: thermal equilibrium
if no net heat flows between two objects in thermal contact, we can say their temperatures are equal and they are in thermal equilibrium
what are the freezing and boiling points of water in Celsius and in Fahrenheit? In Kelvin?
FREEZING
Celsius 0, Fahrenheit 32, Kelvin 273
BOILING
Celsius 100, Fahrenheit 212, Kelvin 373
what is the SI unit for temperature?
Kelvin
defn: absolute zero
the reference point for Kelvins
the theoretical temperature at which there is no thermal energy
defn: third law of thermodynamics
the entropy of a perfectly organized crystal at absolute zero is zero
Kelvin and Celsius scales have different zero reference points, but what is the same?
the size of their units
a change of one degree Celsius equals a change of one unit Kelvin
implication: thermal expansion
a change in some physical property of one kind of matter can be correlated to certain temperature markers
once the scale has been set in reference to the decided-upon temperature markers, then the thermometer can be used to take the temperature of any other matter
defn + unit: coefficient of linear expansion
a constant that characterizes how a specific material’s length changes as the temperature changes
unit: K^-1 (or C^-1)
defn + relationship to linear expansion coefficient: coefficient of volumetric expansion
a constant that characterizes how a specific material’s volume changes as the temperature changes
three times the coefficient of linear expansion for the same material
defn: system
the portion of the universe that we are interested in observing or maniuplating
defn: surroundings
the rest of the universe (other than the system)
defn + ex: isolated systems
not capable of exchanging energy or matter with their surroundings
thus the total change in internal energy must be zero
ex: bomb calorimeter
defn + ex: closed systems
capable of exchanging energy, but not matter, with the surroundings
ex: gases in vessels with movable pistons
most of what will be on test day!
defn + ex: open systems
can exchange both matter and energy with the environment
the matter carries energy and more energy may be transferred in the form of heat or work
ex: boiling pot of water, human beings, uncontained combustion reactions
defn: state functions
thermodynamic properties that are a function of only the current equilibrium state of a system
they are independent of the path taken to get to a particular equilibrium state
what are the 8 state functions?
- pressure
- density
- temperature
- volume
- enthalpy
- internal energy
- Gibbs free energy
- entropy
defn: process functions (what are the two)
describe the path taken to get from one state to another
- work
- heat
defn: first law of thermodynamics
the change in the total internal energy of a system is equal to the amount of energy transferred in the form of heat to the system MINUS the amount of energy transferred from the system in the form of work
describe the sign convention and meaning for the three variables in the first law of thermodynamics
CHANGE IN INTERNAL ENERGY
Positive: increasing temperature
Negative: decreasing temperature
HEAT
Positive: heat flow into system
Negative: heat flows out of system
WORK
Positive: work is done by the system (expansion)
Negative: work is done on the system (compression)
defn: second law of thermodynamics
objects in thermal contact and not in thermal equilibrium will exchange heat energy such that the object with a higher temperature will give off heat energy to the object with a lower temperature until both objects have the same temperature at thermal equilibrium
defn: heat
the process by which a quantity of energy is transferred between two objects as a result of the difference in temperature
can heat ever spontaneously transfer energy from a cooler object to a warmer one?
if work is being done on the system
what are the three ways by which heat can transfer energy?
- conduction
- convection
- radiation
defn: conduction
the direct transfer of energy from molecule to molecule through molecular collisions
what is something implied by the definition of conduction about the objects?
they must be in direct physical context
define conduction at the atomic level
the particles of the hotter matter transfer some of their kinetic energy to the particles of the cooler matter through collisions between the particles of the two materials
why are metals the best heat conductors?
metallic bonds contain a density of atoms embedded in a sea of electrons which facilitate rapid energy transfer
why are gases the poorest heat conductors?
there is so much space between individual molecules that energy-transferring collisions occur relatively infrequently
what is an example of heat transfer through conduction?
the heat that is conducted to your fingers when you touch a hot stove
defn: convection
the transfer of heat by the physical motion of a fluid over a material
why can only liquids and gases transfer heat by convection?
because it involves flow
why are convection ovens more rapid cooks than radiation only ovens?
because heat is transferred to the food by both convection and radiation rather than jUST radiation
convection can be used to wick heat energy away from a hot object, what is one example?
a running cold-water bath may be used to rapidly cool a reaction
defn: radiation
the transfer of energy by electromagnetic waves
how do radiation ovens work?
electrical coils or gas flames are used to heat the insulated box that forms the oven body
the hot metal box then radiates the energy through the open space of the oven, where it is absorbed by whatever food is placed inside
what is the method of heat transfer that the sun uses to warm the Earth?
radiation
what is the one type of heat transfer that can transfer energy through a vacuum?
radiation
defn: specific heat (c) of a substance
the amount of heat energy required to raise one gram of a substance of one degree Celsius or one unit kelvin
explain the concept behind specific heat
when heat energy is added to or removed from a system, the temperature of that system will change in proportion to the amount of heat transfer, unless the system is undergoing a phase change during which the temperature is constant
does the specific heat of a substance change?
yes! according to its phase
are phase changes associated with temperature changes?
no! phase changes occur at a constant temperature
the temperature will not begin to change until all of the substance has been converted from one phase into the other
are phase changes related to change in kinetic or potential energy?
potential!
what does increased freedom of movement allow for for water molecules?
a greater number of microstates
what are the common terms used for the six phase changes?
- solid to liquid: FUSION (melting)
- liquid to solid: FREEZING (solidification)
- liquid to gas: boiling, evaporation, or vaporization
- gas to liquid: condensation
- solid to gas: sublimation
- gas to solid: deposition
at what point do freezing and melting occur at? what is the corresponding heat of transformation?
melting point
heat of fusion
at what point do vaporization and condensation occur at? what is the corresponding heat of transformation?
the boiling point
heat of vaporization
what are the three thermodynamic processes that are considered as special cases of the first law? briefly explain them each.
ISOTHERMAL = constant temperature, therefore no change in internal energy
ADIABATIC = no heat exchange
ISOVOLUMETRIC = no change in volume, therefore no work is accomplished = aka ISOCHORIC
defn: isobaric processes
occur at a constant pressure
what is one implication about energy of the second law of thermodynamics
energy is constantly dispersed
defn: second law of thermodynamics (energy)
energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so
defn: entropy
the measure of the spontaneous dispersal of energy at a specific temperature: how MUCH energy is spread out or how WIDELY spread out energy becomes in a process
how does entropy increase or decrease when energy is distributed into or out of a system?
energy is distributed INTO a system at a given temp: entropy INCREASES
energy is distributed OUT of a system at a given temp: entropy DECREASES
does the concentration of energy happen spontaneously in a closed system?
no! work usually has to be done to concentrate energy
why is the second law of thermodynamics referred to as time’s arrow?
there is a unidirectional limitation on the movement of energy by which we recognize before and after or new and old
energy in a closed system will spontaneously spread out and entropy will increase if it is not hindered from doing so
what is the key to a reversible reaction?
that is goes so slowly that the system is always in equilibrium and no energy is lost or dissipated
(no real processes are ever reversible, it can only be approximated)
defn: reversible process
processes that can spontaneously reverse course
are irreversible/reversible the same thing in chemistry and in physics?
no! think about it
freezing and melting of water are chemically reversible, but physics wise are irreversible (ice will not melt if it stays in the cold environment)
