What are temperature and heat?

Are they the same?

What causes heat?

How do we measure

temperature?What are we

actually measuring?

Temperature and Its MeasurementHow do we measure temperature?Thermometer: Device with a physical

property that changes with temperature and can be easily measured quantitatively.

If two objects are in contact with one another long enough, the two objects have the same temperature (thermal equilibrium).

Two or more objects in thermal equilibrium have the same temperature.

Zeroth law of thermodynamics.

Temperature Scales

The first widely used temperature scale was devised by Gabriel Fahrenheit.

Water freezing point: 32FWater boiling point: 212F

Another widely used scale was devised by Anders Celsius.

Water freezing point: 0C.Water boiling point: 100C

Temperature Scales

Conversion between two scales:

E1. An object has a temperature of 45C. What is its temperature in degree Fahrenheit?

E2. The temperature of a winter day is 14F. What is the temperature in degree Celsius?

TC 5

9TF 32

TF 9

5TC 32

Zero TemperatureThe zero point on the

Fahrenheit scale was based on the temperature of a mixture of salt and ice in a saturated salt solution.

The zero point on the Celsius scale is the freezing point of water.

Both scales go below zero.Is there an absolute

zero?

What is absolute zero?If the volume of a gas is kept

constant while the temperature is different, the pressure will be different.

The Third Temperature Scale

Absolute Temperature Scale (Kelvin Scale)

ExampleWater freezing point: 0C =273.2 K.Water boiling point: 100C = 373.2 K

TK TC 273.2

Heat and Specific Heat Capacity

Steel has a lower specific heat capacity than water.

Specific Heat Capacityspecific heat capacity (c): the quantity of heat needed to

change a unit mass (1 g) of the material by a unit amount in temperature (1 C). It is a property of the material, determined by experiment.The specific heat capacity of water is 1 cal/gC

Table 10.1 Specific capacity of some common substances

Substance Specific Heat Capacity (in Cal/g/C)Water 1.0Ice 0.49Steam 0.48Ethyl alcohol 0.58Glass 0.20Aluminum 0.215

When a material’s temperature is changed, we can calculate how much heat absorbed/released by the material:

Q = mcT where Q = quantity of heat

m = massc = specific heat capacityT = change in temperature

Example: E6 How much heat is required to raise the temperature of

70g of water from 20C to 80C

Heat and TemperatureHeat:

Heat is the energy that flows from one object to another when there is a difference in temperature between the objects. Heat is the average kinetic energy of atoms or molecules making up the system.

Temperature: Temperature is an indication of whether or not and in which direction, the heat will flow (Temperature is an indication of the average of kinetic energy of atoms or molecules).

Phase Change and Latent HeatWhen an object goes through a change of phase

or state, heat is added or removed without changing the temperature. Instead, the state of matter changes: solid to liquid, for example.

The amount of heat needed per unit mass to produce a phase change is called the latent heat (L)The latent heat of fusion of water is 80 cal/g (Lf =

80 cal/g is 80 cal/g): it takes 80 calorie of heat the melt 1 g of ice at 0C to become water at 0C.

The latent heat of vaporization of water is 540 cal/g (Lv = 540 cal/g): it takes 540 calories of heat to turn one gram of water at 100 C into steam at 100 C.

If the specific heat capacity of ice is 0.5 cal/gC°, how much heat would have to be added to 200 g of ice, initially at a temperature of -10°C, to

(a) raise the ice to the melting point?(b) complete melt the ice?

Example Box 10.1

Heat and Mechanic Energy

Benjamin Thompson (1753-1814) noticed that cannon barrels and drill bits became hot during drilling.

Joule performed a series of experiments showing that mechanical work could raise the temperature of a system.

1 cal = 4.19 J

First law of Thermodynamics.

Energy Conservation - In an isolated system, the total amount of energy, including heat, is conserved.

Applying the First Law of Thermodynamics

Example (Box 10.2) :A hot plate is used to transfer 400 cal of heat to a beaker containing ice and water. 500 J of work are also done on the contents of the beaker by stirring.

a) What is the increase in internal energy of the ice-water mixture?

b) How much ice melts in this process?

Counting Food CaloriesCalories in Physics and in food:

In Physics: 1 calories is the amount of energy needed to raise the temperature of 1 g of water 1 C.

In food: 1 Calories is the amount of energy needed to raise the temperature of 1 kg water 1 C

1 Cal =1,000 calNormal body maintenance uses up about 15 calories

per day for each pound of body weight. You must consume about 3500 calories to gain a

pound of weight.To burn off 500 calories you would have to run 5

miles, bike 15 miles, or swim for an hour.

The Flow of Heat

Three basic processes for heat flow:

Conduction

Convection

Radiation

A metal block at room temperature will feel colder than a wood block of the exact same temperature. Why?

The rate of heat flow depends on: a) the temperature difference between the objects.b) the thermal conductivity of the materials, a measure of how well the materials conduct heat.

Conduction: heat flow when in contact

Convection: heat is transferred by the motion of a fluid containing thermal energy.

Radiation, heat energy is transferred by electromagnetic waves. can take place across a vacuum.

What heat-flow processes are involved in the greenhouse effect?

Lab T4. Measurement of the specific heat

Example: Suppose that you have 100 g of water at the temperature of 20 C, and you have 50 g of a metal at the temperature of 100 C. If you put the metal into the water, and the final temperature is 30 C when the mix of water and aluminum reaches a thermal equilibrium, what is the specific capacity of the metal?