Unit 3
Temperature and Heat
• What is temperature?
• What is heat?
• Specific Heat
• Latent Heat and phase changes
Heat and Temperature Unit 03, Slide 1
Temperature
Tells us the average translational kinetic energy of the particles
Related to Internal Energy of system
Heat and Temperature Unit 03, Slide 2
Temperature Scales
Fahrenheit
Water Freezes 32oF
Water Boils 212oF
Celcius
Water Freezes 0oC
Water Boils 100oC
oF = 9/5oC + 32o
oC = 5/9(oF – 32o)
At standard pressure and
temperature (STP)
Heat and Temperature Unit 03, Slide 3
Heat and Temperature Unit 03, Slide 4
Example 3.1: Temperature Conversion
“Double it, add 30o”
“Subtract 30o, divide by 2”
What is 40oF in Celsius?
oC = 5/9(oF – 32o)
= 5/9(40o -32o)
= 4.4oC
Heat and Temperature Unit 03, Slide 5
Temperature Scales II
Does a gas have zero kinetic energy at zero degrees Celsius?
Temperature (oC)
Pre
ssure
- 273.15oC 0oC
-273.15oC = 0K(“zero kelvin”)
-459.67oF= 0oR (“zero degrees Rankine”)
Heat-Work-Temperature
Heat and Temperature Unit 03, Slide 6
Work Heat
• Heat (Q) - how thermodynamic energy is transferred into or out of a system
• Work (W) - how mechanical energy is transferred into or out of a system
Object can not “contain heat”. (Something can’t “contain work”)
Heat and Temperature Unit 03, Slide 7
Heat
Gravity can add transfer energy to ball via work (Dh 0)
transfer energy to box via heat (DT 0)280K 300K280K
Heat and Temperature Unit 03, Slide 8
Units
Calorie = amount of energy to raise one gram of water from 14.5oC to 15.5oC
British Thermal Unit (BTU) = amount of energy to raise one pound of water from 63oF to 64oF
1 Calorie = 3.97 X 10-3 BTU = 4.186 Joule
Heat and Temperature Unit 03, Slide 9
Temperature and Heat
Heat (Q) Temperature(T) increases
But how much?
Q=C*DT heat capacity
Q=c*m*DT specific heat capacity
Q=cm*n*DT molar heat capacity
Heat and Temperature Unit 03, Slide 10
Specific Heat
c (kJ/kg K) cm (kJ/mole K)
Heat and Temperature Unit 03, Slide 11
Example 3.1: Specific Heat
Using a Bunsen burner in chemistry lab 25kJoule of heat is added to 0.32 kg of a liquid. The liquid’s temperature goes from a room temperature of 20oC to around 60oC.
What is the heat capacity of the amount of the liquid?
What is the specific heat capacity of liquid?
Heat and Temperature Unit 03, Slide 12
Example 3.2: Specific Heat
How much heat is needs to be added to raise 2kg of aluminum from 10o to 20oC?
How much heat is needs to be added to raise 2kg of water from 10o to 20oC?
Heat and Temperature Unit 03, Slide 13
Example 3.3: Heat Transfer
A 2.5kg block of aluminum at 20oC is dropped into a bath of 2.5kg of water at 10oC.
The water and block are both placed inside a “super insulator” that will not allow any heat transfer in or out of the system.
What is the final temperature of the block/water system after they come to thermal equilibrium?
(QNET=0)
Tem
per
atu
re (
T)
Heat and Temperature Unit 03, Slide 14
Latent Heat
Heat In (Q)
1dT
dQ c
Qv
LV = Latent Heat of Vaporization = amount of heat required to change the phase of 1kg from liquid to gas
Qv = m*Lv
Heat and Temperature Unit 03, Slide 15
Latent Heats
Tem
per
atu
re (
T)
Heat and Temperature Unit 03, Slide 16
Why steam is so dangerous
Heat In (Q)
101oC
99oC
Heat and Temperature Unit 03, Slide 17
The Pepsi starts out at room temperature (20oC) and the ice starts at -10oC. What is the final temperature after the system has come to thermal equilibrium?
A one liter bottle of Pepsi is placed in our “super cooler” along with six cubes of ice. The ice cubes are around 3cm on a side and so have a mass of 27gram each.
Example 3.4: Heat Transfer II
Heat and Temperature Unit 03, Slide 18
What is the final temperature after the system has come to thermal equilibrium?
What if all the initial conditions had been the same except you had put in 14 cubes of ice instead of 6?
Example 3.5: Heat Transfer with more ice
Heat and Temperature Unit 03, Slide 19
How much of the ice will melt?
What if all the initial conditions had been the same except you had put in 14 cubes of ice instead of 6?
Example 3.6: Heat Transfer with more ice