Thermodynamics Flashcards
Thermodynamics
The study of heat and its effects
Temperature
A measure of the random kinetic energy of the molecules of a substance
How do Fahrenheit, Celsius, and Kelvi relate to one another?
Absolute zero: 0 K, -273 degrees Celsius, and -460 degrees Fahrenheit
Freezing Point of Water: 273 K, 0 deg Celsius, and 32 deg Fahrenheit
Boiling Point of Water: 373 K, 100 deg Celsius, and 212 deg Fahrenheit
T(Celsius) = T(Kelvin) - 273
T(Fahrenheit) = 9/5 T(Celsius) + 32
Thermal Expansion
ΔL = α L ΔT
Where α is a constant that describes how a specific material’s length changes as temperature changes
Volume Expansion
ΔV = β V ΔT, where β = 3α
Heat
The energy transferred between two objects as a result of a difference in temperature. Work has to occur in order for heat to transfer from a cooler body to a warmer body.
Conduction
Heat transfers through molecular collisions or direct contact. Metals are the best heat conductors due to their mobile electrons, while gases tend to be poor heat conductors.
Convection
Heat transfers through the physical motion of the heated material, taking place only in liquids and gases. Heated portions rise while cooler portions sink.
Radiation
Heat transfers through electromagnetic radiation.
Why do thermos bottles have a shiny surface on the inside?
The shiny surface reflects electromagnetic radiation back into the liquid, slowing down heat loss.
Units for heat
1 Calorie = 1000 calories = 3.97 Btu = 4184 J
Specific Heat
Q = mc ΔT = mc(T(final) - T(initial))
Q > 0, heat gain
Q < 0, heat loss
This equation should be used when no phase transition occurs.
Heat of Transformation
The amount of heat required for a phase change, where q = mL
How does temperature change during a phase transition?
Temperature does not change during a phase transition, remaining constant.
Heat of Fusion
The heat of transformation corresponding to a phase change involving liquids and solids
Heat of Vaporization
The heat of transformation corresponding to a phase change involving liquids and gases
Pressure
P = F/ A, where units = Pa = N/ m^2 = kg/ (m s^2)
1 atm = 1.013 X 10^5 Pa
Gas pressure on the container is due to the individual molecular forces the gas exerts on the wall of the container.
In problems of thermodynamics, describe the difference between work done BY a gas and work done ON a gas
Work done BY the system is positive, increasing the volume of the gas, while work done ON the system is negative, decreasing the volume of a gas.
Work
W = P ΔV
In graphs of P v. V, the total area under the graph is the work done.
What is the term for when the pressure remains constant?
Isobaric
First Law of Thermodynamics
ΔE = Q - W (remember that W done BY system is + and W done ON system is - and heat absorbed is + while heat lost is -)
What are some special cases of the First Law of Thermodynamics?
Adiabatic (Q = 0) ----- ΔU = -W Constant Volume (W = 0) ----- ΔU = Q Closed Cycle (ΔU = 0) ----- Q = W
When does internal energy increase (ΔU > 0)?
When Q > 0, heat absorbed, and W < 0, work done ON system
When does internal energy decrease (ΔU < 0)?
When Q < 0, heat lost, and W > 0, work done BY system
Second Law of Thermodynamics
The entropy of a system combined with the surrounding will either increase (for irreversible processes) or not change (for reversible processes)
Isothermal Processes
Processes where the temperature remains constant throughout.
Entropy = ΔS = Q/T for reversible, isothermal processes
