Unit 3 Temperature and Heat - College of DuPage 3 Temperature and Heat • What is temperature? ... (STP) Heat and Temperature Unit 03, ... A one liter bottle of Pepsi is

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