1 Introduction Physics 313 Professor Lee Carkner Lecture 1

2 What is Thermodynamics? Hot and cold and how they get that way Classical Thermodynamics –Temperature, heat and work can be transformed into one another Statistical Physics –The behavior of particles is governed by the laws of probability

Laws of Thermodynamics Zeroth Law –Temperature always means the same thing 1st Law –Energy is conserved 2nd Law –Randomness always increases 3rd Law –Randomness decreases with decreasing temperature

4 Thermal Equilibrium Two objects at different temperatures placed together will exchange heat until they are at the same temperature Zeroth Law: –If A and B are each in thermal equilibrium with T then they also are in thermal equilibrium with each other

Temperature For temperature it is best to use the Kelvin scale: T K = T C T F = (9/5)T C + 32 Temperature is a measure of the random motions of the molecules of a substance: v rms = (3RT/M) ½ K ave = (3/2)kT  E int = nC V  T

6 Heat Heat is energy transferred between two substances as a result of a temperature difference The amount of heat needed to change temperature is: Q = cm(T f - T i ) The amount of heat needed to change phase is: Q = Lm

Work Work is the energy change associated with expansion or contraction W = integral [p dV] Work only occurs with a change of volume –If the volume increases, work is done by the system and the work is positive –If the volume decreases work is done on the system and the work is negative

8 Internal Energy Internal energy is a measure of the energy of the molecules of a substance and depends only on temperature:  E int = nC V  T C V = (3/2)R R = 8.31 J/mol K

9 First Law of Thermodynamics The first law always holds in any situation:  E int = Q - W Energy is conserved –You cannot get more out of a system than you put into it

10 Heat Transfer Conduction H = Q/t = A(T H -T C ) /  (L/k) Radiation P r =  AT 4 –Net power is power received minus power emitted Convection –Hot fluid rises in a gravitational field moving heat with it

11 Ideal Gas Most gasses can be approximated as ideal gases M = mN A N A = 6.02 X (Avogadro’s number) Ideal Gas Law: pV = nRT n (number of moles) and R (gas constant) do not change for any given amount of gas

12 First Law and Ideal Gas Any ideal gas must obey: pV = nRT  E int = Q - W  E int = n C V  T Q = n C  T W = integral [p dV]

13 Entropy High entropy means high randomness Entropy always increases  S = S f -S i = integral [dQ/T] For isothermal processes:  S = Q/T First Law: output cannot exceed input Second Law: output cannot equal input

14 Adiabatic Definition –No heat pV , TV  are constant Heat, Work and Internal Energy Q = 0 W = -  E int = -n C V  T

15 Isochoric Definition –Constant volume Heat, Work and Internal Energy Q =  E int = n C V  T W = 0

16 Isothermal Definition –Constant temperature Heat, Work and Internal Energy Q = W = nRT ln (V f /V i )  E int = 0

17 Isobaric Definition –Constant pressure Heat, Work and Internal Energy Q = n C p  T W = p  V  E int = n C V  T