Chapter 18: Temperature & Heat
What is thermodynamics about?
What is a thermometer, and how does it work?
a device which experiences a change in some physical property due to
changes in temperature
Three laws (actually four) of thermodynamics.
The zeroth law says: If A = C and B = C then A = B
Constant-volume gas thermometer: (pending the volume is constant), the absolute
temperature is proportional to the absolute pressure.
The triple point of water is 273.16 K, and the kelvin (degree) is defined to be
1/273.16 of the temperature of the triple point.
The Celsius, Fahrenheit and Kelvin Scales:
T = TC + 273.15
TF = 9/5 TC + 32
DT = DTc = 5/9 DTF
Thermal expansion of solids and liquids:
Coefficient of linear expansion: a
Coefficient of volume expansion: b = 3a
DL = a Lo DT
DV = 3a V DT
DA = 2a A DT
Can a be negative? Calcite/ water
How does a thermostat work? the bimetallic strip
a is greater in gases than in liquids; greater in liquids than in solids
What is: Internal energy, Thermal energy and Thermal energy
transfer (heat)?
What does: Q = 0 mean? What does: Q < 0 mean?
What are the common units of heat?
Q = C DT = m c DT
What are the units of c or C?
Q=mL
What are the units of L?
Work: W = dW = p dV
The ‘amount’ of work is the area under the p-V diagram curve.
What does: W = 0 mean? What does: W < 0 mean?
FLTD:
DEint = Eint,f - Eint,i = Q - W
Adiabatic process:
Q = 0, DEint = -W
Adiabatic Free Expansion in ideal gas: no work, DEin = 0; so, T
does not change.
Constant volume (Isovolumetric) process:
W = 0, DEint = Q
Cyclical process:
• No change in system properties including internal energy!
• DEint = 0
• Q =W
Conduction:
Pcond = Q/t = (-) k A DT/L
k: thermal conductivity. Large k means good conductors