Concept Summary

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Self-Assessment Tests—qualitative and quantitative questions with extensive feedback.

Topic | Discussion | Learning Aids
Celsius temperature scale Fahrenheit temperature scale | 12.1 COMMON TEMPERATURE SCALES On the Celsius temperature scale, there are 100 equal divisions between the ice point (0 °C) and the steam point (100 °C). On the Fahrenheit temperature scale, there are 180 equal divisions between the ice point (32 °F) and the steam point (212 °F). |
Kelvin temperature scale | 12.2 THE KELVIN TEMPERATURE SCALE For scientific work, the Kelvin temperature scale is the scale of choice. One kelvin (K) is equal in size to one Celsius degree. However, the temperature T on the Kelvin scale differs from the temperature Tc on the Celsius scale by an additive constant of 273.15:

| (12.1)

Absolute zero | The lower limit of temperature is called absolute zero and is designated as 0 K on the Kelvin scale. |
Thermometric property | 12.3 THERMOMETERS The operation of any thermometer is based on the change in some physical property with temperature; this physical property is called a thermometric property. Examples of thermometric properties are the length of a column of mercury, electrical voltage, and electrical resistance. |
Linear thermal expansion | 12.4 LINEAR THERMAL EXPANSION Most substances expand when heated. For linear expansion, an object of length L0 experiences a change in length when the temperature changes by :

| (12.2)

where is the coefficient of linear expansion.
Thermal stress | For an object held rigidly in place, a thermal stress can occur when the object attempts to expand or contract. The stress can be large, even for small temperature changes. |
How a hole in a plate expands or contracts | When the temperature changes, a hole in a plate of solid material expands or contracts as if the hole were filled with the surrounding material. |
Volume thermal expansion | 12.5 VOLUME THERMAL EXPANSION For volume expansion, the change in the volume of an object of volume V0 is given by

| (12.3)

where is the coefficient of volume expansion.
How a cavity expands or contracts | When the temperature changes, a cavity in a piece of solid material expands or contracts as if the cavity were filled with the surrounding material. |

Use Self-Assessment Test 12.1 to evaluate your understanding of Sections 12.1–12.5.

Internal energy Heat | 12.6 HEAT AND INTERNAL ENERGY The internal energy of a substance is the sum of the kinetic, potential, and other kinds of energy that the molecules of the substance have. Heat is energy that flows from a higher-temperature object to a lower-temperature object because of the difference in temperatures. The SI unit for heat is the joule (J). |
Heat needed to change the temperature | 12.7 HEAT AND TEMPERATURE CHANGE: SPECIFIC HEAT CAPACITY The heat Q that must be supplied or removed to change the temperature of a substance of mass m by an amount is

| (12.4)

where c is a constant known as the specific heat capacity.
Energy conservation and heat | When materials are placed in thermal contact within a perfectly insulated container, the principle of energy conservation requires that heat lost by warmer materials equals heat gained by cooler materials. |
Mechanical equivalent of heat | Heat is sometimes measured with a unit called the kilocalorie (kcal). The conversion factor between kilocalories and joules is known as the mechanical equivalent of heat:

Heat needed to change the phase | 12.8 HEAT AND PHASE CHANGE: LATENT HEAT Heat must be supplied or removed to make a material change from one phase to another. The heat Q that must be supplied or removed to change the phase of a mass m of a substance is

| (12.5)

where L is the latent heat of the substance and has SI units of J/kg. The latent heats of fusion, IS 12.61 vaporization, and sublimation refer, respectively, to the solid/liquid, the liquid/vapor, and the solid/vapor phase changes.
Vapor pressure curve | 12.9 EQUILIBRIUM BETWEEN PHASES OF MATTER The equilibrium vapor pressure of a sub-Ex. 16 stance is the pressure of the vapor phase that is in equilibrium with the liquid phase. For a given substance, vapor pressure depends only on temperature. For a liquid, a plot of the equilibrium vapor pressure versus temperature is called the vapor pressure or vaporization curve. |
Fusion curve | The fusion curve gives the combinations of temperature and pressure for equilibrium between solid and liquid phases. |
Relative humidity | 12.10 HUMIDITY The relative humidity is defined as follows:

| (12.6)

Dew point | The dew point is the temperature below which the water vapor in the air condenses. On the vaporization curve of water, the dew point is the temperature that corresponds to the actual pressure of water vapor in the air. |

Use Self-Assessment Test 12.2 to evaluate your understanding of Sections 12.6–12.10.

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