Chapter 7: Thermal Properties of Matter Physics Chapter 7: Thermal Properties of Matter
Objectives Explain the concept of temperature in terms of thermal equilibrium and kinetic energy of atoms and molecules. Describe the Celsius, Fahrenheit, and Kelvin temperature scales, and convert temperatures from one scale to another . Calculate the linear thermal expansion of a solid
Temperature The study of the thermal properties of matter is called thermodynamics, which is governed by the laws of thermodynamics. One of the key concepts in thermodynamics is temperature, and you will learn how it is measured.
Temperature (cont.) In physics, temperature can be defined in two ways: In terms of thermal equilibrium. In terms of the kinetic energy of atoms and molecules.
Thermal Equilibrium When two hot and cold bodies come into contact, heat flows from the hotter to the colder body. When this heat flow stops, the bodies are said to have attained thermal equilibrium. The zeroth law of thermodynamics states that if two bodies, A and B, are each in thermal equilibrium with a third body, C, A, and B are in thermal equilibrium with each other.
Temperature and the Kinetic Theory of Gases Temperature can be interpreted as the kinetic energy possessed by the atoms and molecules of an object. When the temperature of a gas increases, the atoms or molecules that constitute the gas, whiz around at a higher speed. The kinetic energy that these atoms and molecules possess is what we measure as the temperature of the gas.
Measurement of Temperature We will discuss the main temperature scales used to measure and specify temperature. This is done by using some reproducible phenomenon, such as the boiling and melting points of water, for the centigrade scale. The three main temperature scales used for measuring temperature are: Celsius Fahrenheit Kelvin
Measurement of Temperature (cont.) On the Celsius scale, the freezing point of water is a temperature of 0°C, and the boiling point of water is a temperature of 100°C. On the Fahrenheit scale, the freezing point of water is 32°F, and the boiling point of water is 212°F. The reference point on the Kelvin scale is specified as the triple point of water, that is, liquid, ice, and vapour.
Celsius, Fahrenheit, and Kelvin Temperature Scales The reference points in Celsius, Fahrenheit, and Kelvin Temperature scales are shown below:
Thermal Expansion
Linear Expansion The coefficients of linear expansion for some common materials are listed in the following table:
Volume Expansion When the temperature of a solid or a liquid increases, the solid or liquid increases in volume. The increase in volume is given by the equation: For a solid, the coefficient of volume expansion is related to the coefficient of linear expansion by the formula:
Summary In physics, temperature can be defined in two ways: In terms of thermal equilibrium. In terms of the kinetic energy of atoms and molecules. The zeroth law of thermodynamics states that if two bodies, A and B, are each in thermal equilibrium with a third body, C, A, and B are in thermal equilibrium with each other. Temperature can be interpreted as the kinetic energy possessed by atoms and molecules of an object.
Summary (cont.) The three main temperature scales used for measuring temperature are: Celsius Fahrenheit Kelvin Most materials change their dimensions when their temperature changes. When the temperature of a solid or a liquid increases, the solid or liquid increases in volume. A calorie is defined as the amount of heat required to raise the temperature of 1 g of water by 1°C
Summary (cont.) The quantity of heat that an object or material absorbs (or loses) when heated is reflected in the heat capacity or the specific heat of an object. Heat is transferred by the following processes: Conduction Convection Radiation An ideal gas equation describes the relation between the pressure, temperature, and volume of an ideal gas.