Chapter 4: Thermodynamics Flashcards
The zeroth law of thermodynamics states:
objects are in thermal equilibrium (there is no net transfer of heat) when they are at the same temperature; if a=b and b=c, then a=c
Temperature is:
a physical property of matter related to the average kinetic energy of particles.
Differences in temperature determine:
the direction of heat flow (heat flows from hot to cold)
Heat (energy) spontaneously flows from:
hot temperatures to cold temperatures
If no net heat flows between two objects in thermal contact, we can say that:
their temperatures are equal and they are in thermal equilibrium
Absolute zero
the temperature at which all random atomic motion stops because there is zero thermal energy (0 degrees Kelvin is absolute zero)
Kelvin to Celsius Equation
Tc = Tk - 273
Celsius to Fahrenheit Equation
Tf = (9/5)Tc + 32
Thermal Expansion is:
The change in an object’s size with a change in temperature. In general, objects expand as the temperature increases.
The change in length of a solid object due to temperature can be found with what equation?
ΔL = αLΔT
(where ΔL is the change in length; L is the original length; ΔT is the change in temperature; and α is the coefficient of linear expansion of the object)
The change in volume of a liquid or solid object due to temperature can be found with what equation?
ΔV = **βVΔT**
(where ΔV is the change in volume; β is 3α; V is the original volume; and ΔT is the change in temperature)
First Law of Thermodynamics states:
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.
The internal energy of a system can be increased by:
adding heat, doing work on the system, or some combination of both processes.
The change in internal energy (ΔU) of a system is calculated from what equation?
ΔU = Q - W
(where ΔU is the change in internal energy of the system; Q is the energy transferred through heat to the system; and W is the work done by the system).
NOTE: work done on the system and heat flow out of the system are always negative; opposite is positive.
Work done by a system is always:
positive
Work done on a system is always:
negative
Heat flow into a system is always:
positive
Heat flow out of a system is always:
negative
A system is:
the object we are paying attention to
An environment is:
everything surrounding the system that is not a part of the system
Energy be can be neither:
created or destroyed. Thus, the energy of a closed system will always be constant.
Work is the process by which:
energy is transferred as the result of force being applied through some distance (W=Fdcosθ)
The only two process by which energy can be transferred from one object to another are:
work and heat
Heat is the process of:
energy transfer between two objects at different temperatures and one that will continue until the two objects come into thermal equilibrium (i.e. reach the same temperature)
In regards to heat, the second law of thermodynamics states:
objects in thermal contact and not in thermal equilibrium will exchange heat energy such that the object with the higher temperature will give off heat energy to the object with a lower temperature until both objects have the same temperature (i.e. reach thermal equilibrium)
The four different units of heat:
Joules (J); calories (cal); British Thermal Unit (Btu); Calorie (Cal)
The conversion factors between the units of heat:
1 Cal = 103cal = 3.97 Btu = 4,184 J
The three means by which heat can transfer energy:
conduction, convection, and radiation
Conduction is:
the direct transfer of energy from molecule to molecule through molecular collisions (there must be physical contact between two objects for conduction to occur)
A good conductor and a bad conductor:
Good = Metals; Bad = Gases. This is because metal is more dense, thus it will have more molecular collisions and more transfer of heat energy during these collisions.
Convection is:
the transfer of heat by the bulk physical motion of the heated material. Only liquids and gases can transfer heats through convection.
Radiation is:
the transfer of energy by electromagnetic waves.
True/False: Radiation can travel through a vacuum.
True
Specific Heat (c) is:
the amount of heat energy required to raise 1 kg of a substance by 1 degree Celsius or 1 Kelvin
The equation used to determine the heat gained or lost by a substance subjected to a change in temperature:
Q = mcΔT = mc(Tf- Ti)
(where m is the mass of the object and c is the specific heat)
Phase changes are related to changes in:
potential energy
Adding heat raises the temperature of a system because the particles in that system now have a greater:
average kinetic energy
During a phase change of an object, there is no:
temperature change.
The equation used to determine the heat gained or lost by a substance subjected to a change in phase:
Q = mL (where Q is the amount of heat gained or lost; m is the mass of the substance; and L is the heat of transformation of the substance)
The phase change from liquid to solid / solid to liquid is known as:
the heat of fusion
The phase change from liquid to gas/ gas to liquid is known as:
heat of vaporization
During any thermodynamic process, a system goes from some initial equilibrium state with an initial temperature, intial pressure, and initial volume to:
some other equilibrium state, which may be a different temperature, different pressure, and different volume.
The four units of pressure are:
atmosphere (atm); pascal (Pa); torr; mm Hg
The conversion factors between the units of pressure:
1 atm = 1.013 X 105 Pa = 760 torr = 760 mm Hg
When gas expands and pushes up against a piston, the force exerted by the gas is:
F=PA (the volume of the system increases)
When gas is compressed by a piston, the force exerted by the piston is:
F=PA (the volume of the system decreases)
When the volume of a system changes due to an applied pressure, we can say:
work has been done
When work is done by the system, the internal energy of the system:
decreases
When work is done on the system, the internal energy of the system:
increases
When gas expands, work is:
done by the gas and positive
When gas compresses, work is:
done on the gas and negative
You can calculate the work done on or by a system with pressure and volume by finding:
the area under the pressure (y-axis) - volume (x-axis) curve
If volume stays constant while pressure changes, the work done is:
zero
If pressure stays constant while volume changes, the work done is:
the area under the curve, which is rectangular
The equation used to determine the work done on or by a system that undergoes a change in volume at constant pressure:
W=PΔV
Isobaric is:
when a system undergoes a process in which pressure is constant
Isovolumetric (isochoric) is:
constant volume (W=0)
Adiabatic is:
no heat exchange (Q=0)
Closed cycle (isothermal) is:
constant internal energy (deltaU=0)
In an adiabatic system, the first law of thermal dynamics becomes:
ΔU=-W
(because Q=0)
In a isovolumetric system, the first law of thermal dynamics becomes:
ΔU=Q
(because W=0)
In an closed cycle system, the first law of thermal dynamics becomes:
Q=W
(because ΔU=0)
Special Cases of the First Law of Thermodynamics Table:
The second law of thermodynamics:
Energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so.
Entropy is:
the measure of the spontaneous dispersal of energy at a specific temperature: huow much energy is spread out or how widely spread out energy becomes in a process.
The equation used to determine the change in entropy of a system at a given temperature:
** ΔS = Q/T**
(where ΔS is the change in entropy; Q is the heat gained or lost; and T is the temperature in Kelvin)
When energy is distributed INTO a system at a given temperature, its entropy:
increases
When energy is distributed OUT a system at a given temperature, its entropy:
decreases
In order to concentrate / localize energy:
Work must be done
For a reversible process, the entropy can be calculated using the equation:
ΔS = Q/T = L (m/T)
(where L is the latent heat (the heat of fusion or vaporization), m is mass, and T is the constant temperature of the system and environment in Kelvin)
The specific heat of water is:
1000 cal/kg ºC
Every natural process is ultimately:
irreversible; however, under highly controlled conditions, certain equilibrium processes such as phase changes can be treated as reversible.
During a phase change, heat energy causes changes in the particle’s:
potential energy, not kinetic energy, so there is no change in temperature.
