Temperature and Heat - PowerPoint PPT Presentation

1 / 28

Temperature and Heat. Chapter 12. Expectations. After this chapter, students will : know what temperature is be familiar with common temperature scales calculate the changes in the linear dimensions of objects, and the volumes of substances, with temperature

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

Temperature and Heat

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Temperature and Heat

Chapter 12

Expectations

After this chapter, students will:

• know what temperature is

• be familiar with common temperature scales

• calculate the changes in the linear dimensions of objects, and the volumes of substances, with temperature

• understand heat as a form of energy

Expectations

After this chapter, students will:

• Use the concept of specific heat capacity to relate temperature changes to gains and losses of heat energy

• Calculate the energy transfers accompanying phase changes of materials

• Analyze situations in which different phases of matter exist in equilibrium

Temperature

Temperature is a rational numerical characterization of the hotness or coldness of an object or a substance.

If a hotter (higher temperature) object touches a colder (lower temperature) one, heat energy tends to flow from the hotter to the colder.

Temperature Scales

Temperature scales are typically based on the phase changes of a very common material: water.

The ice point is the temperature at which liquid water and ice are in equilibrium, at one atmosphere of pressure.

The steam point is the equilibrium for liquid water and steam, at one atmosphere.

Temperature Scales: Celsius

Ice point: 0 °C Steam point: 100°C

Anders Celsius

1701 – 1744

Swedish astronomer

Temperature Scales: Fahrenheit

Ice point: 32 °F Steam point: 212°F

Daniel Gabriel Fahrenheit

1686 – 1736

German physicist

Temperature Scales: Absolute

Ice point: 273.15 K Steam point: 373.15 K

William Thomson

(Lord Kelvin)

1824 – 1907

Scottish mathematician

and physicist

Temperature Scales: Rankine

Ice point: 491.67 °R Steam point: 671.67 °R

William Rankine

1820 – 1872

Scottish engineer

Temperature Conversions

Fahrenheit / Celsius

Celsius / Absolute

Temperature Style and Grammar

Temperature differences or changes are expressed in “Celsius degrees” (C°).

The temperature of an object or substance is expressed in “degrees Celsius” (°C).

The unit of absolute temperature is the “kelvin” (K). There is no such thing as a “degree Kelvin” (°K).

Temperature Expansion – Linear

Most materials expand when they get hotter. As they expand, all their linear dimensions (length, width, height, diameter, etc.) expand proportionally.

The amount of the expansion depends on:

• The amount of temperature change

• The original size of the dimension

• A material property: coefficient of linear expansion

Temperature Expansion – Linear

SI unit for coefficient of linear expansion: (C°)-1

Values of a for some materials are tabulated on

Temperature Expansion – Volume

SI unit for coefficient of volume expansion: (C°)-1

Values of b for some materials are tabulated on

Temperature and Heat

Heat is the energy that moves from an object or substance at higher temperature to an object or substance at lower temperature because of their temperature difference.

SI unit of heat: the joule (J).

Temperature and Heat

When heat flows from a hotter object into a colder one, the internal energy of the hotter object decreases, and the internal energy of the colder object increases.

The internal energy consists of several forms of molecular kinetic and potential energy. Temperature is not a measure of an object’s total internal energy.

Temperature and Heat

Does the same amount of heat energy, flowing into or out of a variety of objects, change every object’s temperature by the same amount?

No. The change in temperature depends on:

• the amount of heat lost or gained;

• the mass of the object; and

• the material that the object is made of.

Temperature and Heat

The material property is called the specific heat capacity:

SI units of specific heat capacity: J / (kg C°)

temperature change

heat required

specific heat capacity

mass

Heat: Other Units

Satan’s units* for heat:

calorie (cal): the amount of heat that increases the temperature of 1 gram of water by 1 C°

kilocalorie (kcal): increases 1 kg H2O by 1 C°

nutritional Calorie: = 1000 regular calories = 1 kcal

British Thermal Unit (BTU): increases the temperature of 1 pound of water by 1F°

(*Satan loves to spread misery and confusion.)

Heat and Phase Change

To change the phase of a material (melt ice, freeze water, boil water, condense steam) we must add heat, or remove heat.

At the phase-changing temperatures (melting point or boiling point), heat is added or removed without changing the temperature until the phase change is complete.

Heat and Phase Change

The amount of heat required to accomplish the phase change depends on the mass of material involved, what kind of material it is, and what phase change we are considering.

In general:

SI units of latent heat: J / kg

mass

heat

latent heat

Heat and Phase Change

Phase change names

Equilibrium Between Phases

most things contract when they freeze

Fusion curves: temperatures and pressures at which the solid and liquid phases are in equilibrium.

water expands when it freezes

Equilibrium Between Phases

Vaporization curves: temperatures and pressures for liquid – gas equilibrium.

water

Relative Humidity

Partial pressure: when a number of different molecular species are present in a mixture of gases, the total pressure of the mixture is the sum of the partial pressures due to each constituent.

If the partial pressure of water vapor in the atmosphere reaches the equilibrium pressure (from a vaporization curve), water leaves the atmosphere at the same rate it enters. (Fog or rain.)

Relative Humidity

Relative humidity tells how much water vapor is in the air, compared to how much can be in the air.

Relative Humidity

Given an existing partial pressure of water vapor in the air, if the air is cooled, it will reach a temperature for which the equilibrium vapor pressure of water decreases to be equal to the existing partial pressure of water vapor. At that temperature, the relative humidity is 100%, and water starts coming out of the atmosphere. This temperature is called the dew point.