Physics 151: Lecture 38 Today’s Agenda. Today’s Topics (Chapter 20) Internal Energy and Heat Heat Capacity First Law of Thermodynamics Special Processes. Lecture 37: ACT 2 Thermal expansion.
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(a) ball won’t fit(b) fits more easily(c) same as before
(b) fits more easilyLecture 37: ACT 2Solution
After (higher T)
PV = N kBTIdeal gas / Review
R is called the universal gas constant
PV = nRT
In SI units, R =8.315 J / mol·K
kBiscalled the Boltzmann’s constant
kB = R/NA = 1.38 X 10-23 J/K
B = rTo V g
mgLecture 37: Problem 3
(Air density at 10.0°C is 1.25 kg/m3.)
T = 472 K !
1 cal = 4.186 J
Q = CDT
m =4.19 g
Therefore, the work done on the gas is dW = -P dV
W = -Pf (Vf – Vi)
W = -Pi (Vf – Vi)
Which statement below regarding the First Law of Thermodynamics is most correct ?
a. A system can do work externally only if its internal energy decreases.
b. The internal energy of a system that interacts with its environment must change.
c. No matter what other interactions take place, the internal energy must change if a system undergoes a heat transfer.
d. The only changes that can occur in the internal energy of a system are those produced by non-mechanical forces.
e. The internal energy of a system cannot change if the heat transferred to the system is equal to the work done by the system.
for an ideal gas :
PV = nRT and
In an adiabatic free expansion :
a. no heat is transferred between a system and its surroundings.
b. the pressure remains constant.
c. the temperature remains constant.
d. the volume remains constant.
e. the process is reversible.