Chapter 11: Heat Chapter 12: Thermodynamics

Chapter 11: Heat Chapter 12: Thermodynamics Review Chapter 11 Heat heat a form of energy in transit SI unit is the joule (J) common nonstandard units are the kilocalorie (kcal) and the British thermal unit (BTU) mechanical equivalent of heat relates joules to kilocalories 1 kcal = 1000 calories = 1 Calorie = 4,186 J

Memorize this or write it on your blue sheet. heat energy work all have the same units; they are different forms of the same thing thermal conductivity the heat-conducting ability of a material H = Q = KA T t d On Gold Sheet where H is the thermal conductivity of the material

A is the cross-sectional area T is the temperature of the hot side of the conductor minus the temperature of the cold side of the conductor d is the thickness of the conductor ** On the gold sheet L is used to represent thickness. Chapter 12 Thermodynamics The ideal gas law is a thermodynamic equation of state. pV = nRT or pV = NkBT

On Gold Sheet where p is pressure in pascals (Pa) V is volume in cubic meters (m3) n is the number of moles R is the universal gas constant, 8.31 J/(molK) T is the temperature in kelvin N is the number of molecules kB is Boltzmanns constant, 1.38 x 10-23 J/K Know the vocabulary of thermodynamics. Know the 1st Law and sign conventions. The First Law of Thermodynamics is a statement of energy

conservation for thermodynamic systems. U = Q + W On Gold Sheet Q : heat U : change in internal energy W: work Sign Conventions The system is the gas, fluid, etc. you are analyzing. +Q means heat added to the system -Q means heat removed from the system

+W means work done on the system (compression) -W means work done by the system (expansion) isothermal constant temperature U = 0 ; Q = -W As U goes, so goes T. isobaric constant pressure W = - pV On Gold Sheet isometric constant volume W = 0; Q = U adiabatic no heat is exchanged Q = 0; U = W The area under the curve on a P-V graph is equal to work.

Internal energy is linked to temperature. Recall from Chapter 10, for ideal monatomic gases: U = 3/2 nRT or U = 3/2 NkBT The Second Law of Thermodynamics specifies the direction in which a process can naturally or spontaneously take place. Heat does not flow spontaneously from a colder to a warmer body. In a thermal cycle, heat energy cannot be completely transformed into mechanical work. The total entropy of the universe increases in every natural process. The Third Law of Thermodynamics It is not possible to lower

temperature to absolute zero, since it would violate the Second Law: no heat engine can be 100% efficient. heat engines convert heat to work For one cycle, the system returns to the same temperature and heat is converted to work done by the system. QH U = 0; Q = -W W QC thermal efficiency work out divided by work in e=

W Q On Gold Sheet thermal pump the reverse of a heat engine example: a refrigerator Coefficient of performance is a measure of efficiency for a thermal pump QH W QC

Carnot cycle the ideal heat engine give the upper limit of efficiency eC = TH TC TH On Gold Sheet entropy a measure of the disorder of a system The entropy of an isolated system increases for every natural process as well as all irreversible processes, such as free expansion. The entropy of an isolated system stays the same for all reversible processes and reversible cycles. Entropy of an isolated system never decreases. Entropy can only

decrease in a non-isolated system by doing work or expending energy. **Remember to use Kelvin for all thermodynamic formulas.

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