Thermodynamics Flashcards
Define heat.
Transfer of thermal energy from a hotter object to a colder object
What is 0˚ C in Kelvin?
273K
Conversion of F –> C
(9/5)C + 32
When solids or liquids experience a change in temperature, their length or volume changes. What are the corresponding formulas to determine this change?
For ∆L (applicable to solids only):
∆L = αL∆T
For ∆V (solids & liquids):
∆V = βV∆T
**α and β are constant values
State functions
Functions that describe the equilibrium state of a system, independent of the path taken by the system to arrive to its present state
Pressure, volume, temperature, entropy
Process/path functions
Functions that describe the path taken by a system to transition from 1 equilibrium state to another
Work, heat
Equation to calculate total internal energy of a system:
∆U = Q - W
If W is negative, work is being done (on/by) the system.
If W is positive, work is being done (on/by) the system.
-W = work is done on the system
+W = work is done by the system
3 methods of heat transfer:
Conduction, convection, radiation
Conduction
direct transfer of energy through physical contact/molecular collisions
Convection
transfer of heat by the physical motion of a liquid or gas over a material
*SOLIDS don’t participate in convection
Radiation
transfer of energy by electromagnetic waves ;can transfer energy through a vacuum
Ex: Sun warming the Earth
During a phase change, temperature is (changing/constant), even though heat is added or removed.
Constant
SI unit of heat
Joules (J)
Specific heat of water
1 cal/g˚C or 4.184 J/g*K or 420 J/˚C
0th Law of Thermodynamics
Objects that are in thermal contact & not in thermal equilibrium, will exchange heat traveling from the hotter object to the cooler object
1st Law of Thermodynamics
Energy can be transferred, but it isn’t created or destroyed.
2nd Law of Thermodynamics
Entropy of an isolated system always increases; heat will flow from a hotter object to a colder object
Calculating heat energy (q)
q = mC∆T
c is the specific heat capacity
Difference between specific heat capacity and heat capacity
Specific heat capacity - amt. of heat required to raise the temp of 1 g of substance by 1˚C
Heat capacity - amt. of heat required to raise temp of entire sample by 1˚C
Another version of calculating heat:
q = C∆T
no mass required
*If given a problem where one material loses heat & other gains heat, set q’s equal to each other
Change in entropy equation
∆S = Qrev/T
Qrev is the heat gained or lost in a reversible process
T is measured in Kelvin
True or false:
In order to concentrate or confine energy, it requires work.
Yes, because energy spontaneously disperses, so in order for it to be confined some amount of work should be used to confine it to one area.
Calorimeters are an example of what type of system: isolated, closed or open?
Isolated systems because neither energy nor matter is exchanged.
2 main equations to know for calorimeters
- Heat absorbed by calorimeter: Qcalorimeter = Ccalorimeter*∆T
- Qwater/sample = Cmass∆T
The temperature of a system is also a measure of what?
The average kinetic energy of the molecules in that system.
Calculating ∆Eth (change in thermal energy)
∆Eth = (3/2)nR∆T
n is # of moles
R is 8.314
∆T is in K
How does thermal energy change in an isothermal process?
Isothermal - stays the same
When a gas expands, what is true about work?
The work done by the gas is positive.
When a gas is compressed, what is true about work?
The work done by the gas is negative.
W on the gas = - Work by the gas
In a PV graph, if volume stays the same, what is true about work? What if the volume increases?
Work = 0; Work increases
When looking at a PV diagram, how do you calculate work?
Take the area under the curve. Remember the work you calculate is “the work done BY the gas”. To get work done on the gas, take the opposite sign of the same value.
Define the following processes:
Isobaric
Isochoric
Isothermal
Adiabatic
Isobaric - constant pressure
Isochoric - constant volume
Isothermal - constant temperature
Adiabatic - ideal gas is compressed very quickly, no heat exchange occurs between the system & the environment
How do you achieve the following processes?
Isobaric - insuring the piston can move up or down without friction
Isochoric - locking a piston in place
Isothermal - carrying out the process slowly in a cylinder that is in good thermal contact w/ surrounding
Adiabatic - carrying out the process rapidly in a well-insulated cylinder
In an isobaric process, how is the volume affected if the temperature of the process is increased?
Volume increases as temperature increases.
Compare a closed vs. isolated system.
Closed - heat can be exchanged w/ the surroundings, but mass can not be; bomb cell
Isolated - neither heat nor mass can be exchanged w/ the surroundings; calorimeter device
Comparing adiabatic vs. isothermal graph
What is the equation to calculate (energy released/absorbed) during a phase change when temperature is constant.
q = m*L
L is the latent heat of vaporization or latent heat of fusion (usually given in the question)
UNITs are kj/mol or cal/gram
