Thermodynamics Cheat Sheet

13-6-24

Thermodynamics Cheat Sheet

Thermodynamics Cheat Sheet Calorimetry Heat required to change temperature: Q = mcΔT Heat required to change phase: Q = mL Ideal Gas Law: Boyle's Law

PV = nRT (in Kelvin) Constant Temperature PV = constant P1 V1 =P2 V2 Charles/Gay Lussac Law Constant Pressure V/T = constant V1 /T1 =V2 /T2

0th Law: Two objects, each in thermal equilibrium with a third object, are in thermal equilibrium with each other. Math Example: If A = C and B = C, then A = B. 1st Law: The change in internal energy of a system equals the difference between the heat taken in by the system and the work done by the system. Formula: ΔU = Q - W (in Kelvin)

Isothermal no temp change

ΔU = W Q = 0 ΔT = 0 so ΔU = 0 Q = W

Isochoric no volume change

ΔV = 0 so W = 0 ΔU = Q

Adiabatic no heat flow

Isobaric

no pressure change ΔP = 0

W=PΔV

2nd Law: Clausius statement: Heat cannot, by itself, pass from a colder to a warmer body. Kelvin-Planck statement: It is impossible for any system to undergo a cyclic process whose sole result is the absorption of heat from a single reservoir at a single temperature and the performance of an equivalent amount of work. Actual Thermal Efficiency

Ratio of work to heat input

Ideal Thermal Best possible case Efficiency Entropy

How much energy/heat is unavailable for conversion into work

www.yorktech.com/science/craig/PhysicsII/Thermo.htm

Eff = W/QH Ideal Eff = 1TC /TH ΔS = Q/T

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13-6-24

Thermodynamics Cheat Sheet

"Poker game" analogy of the three laws of thermodynamics 0th Law: You can't get out of the game (everything in the universe is in the system, so all objects are in thermal equilibrium or are moving towards it unless we do something about it) 1st Law: You can't win (You can't get something for nothing. If you want work out, you must put heat/energy in and vice versa) 2nd Law: You always lose (Efficiency < 1, Entropy > 0) WebLinks http://hyperphysics.phy-astr.gsu.edu/hbase/heacon.html#heacon Exercise Consider a system that is taken along the paths shown on the P-V diagram. Assume Ua = 30,000 J a) Find the work done by the system in going from a to b. b) Find the work done by the system in going from b to c. c) If 20 kJ of heat enters the system along the path from a to b, what is the internal energy at point b? d) If the internal energy at point c is 95 kJ, how much heat enters or leaves the system along the path from b to c? e) Run it backwards: If 21 kJ of heat enters the system in going from a to d, what is internal energy at point d? f) Run it backwards: Find the heat that enters the system along the path from d to c. g) If the system is taken along the closed loop a→b→c→d→a, how much work is done? h) Find the area of the rectangular path. i) What is the net heat that enters the system?

www.yorktech.com/science/craig/PhysicsII/Thermo.htm

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