Thermal Equilibrium
Thermal equilibrium is the state in which two objects are at the same temperature and no heat flows between them. This is one of the fundamental concepts in thermodynamics and is a prerequisite for many other concepts in the field.
Zeroth Law of Thermodynamics
The Zeroth Law of Thermodynamics states that if two objects are in thermal equilibrium with a third object, then they are also in thermal equilibrium with each other. This law helps establish the concept of temperature and is an important foundation for the study of thermodynamics.
Thermometric Properties
Thermometric properties are physical properties that change with temperature and can be used to measure temperature. Examples of thermometric properties include the expansion of liquids, the resistance of metals, and the voltage produced by certain materials.
Expression for Temperature Based on Two Fixed Points
The expression for temperature based on two fixed points is a method of measuring temperature that relies on the melting and boiling points of a substance. By using two fixed points, a temperature scale can be established that can be used to accurately measure temperature.
Celsius Scale
The Celsius scale is a temperature scale that is based on the melting and boiling points of water. On the Celsius scale, the freezing point of water is 0 degrees and the boiling point of water is 100 degrees.
Absolute Scale (Thermodynamic Scale)
The absolute scale, also known as the thermodynamic scale, is a temperature scale that is based on the concept of absolute zero. On the absolute scale, the temperature is measured in kelvin (K) units, with 0 K representing absolute zero.
Absolute Zero
Absolute zero is the temperature at which all matter has zero thermal energy. This is the lowest possible temperature that can be reached and is the basis for the absolute scale of temperature measurement.
Triple Point of Water
The triple point of water is the temperature and pressure at which water can exist in all three states: solid, liquid, and gas. This is a fundamental concept in thermodynamics and is used as a reference point for temperature measurement.
Expression for Absolute Temperature Based on Triple Point of Water
The expression for absolute temperature based on the triple point of water is a method of measuring temperature that uses the properties of water at its triple point to establish a temperature scale. This method is used to define the kelvin unit of temperature measurement.
Relationship Between Celsius and Absolute Temperatures
The relationship between Celsius and absolute temperatures is based on the fact that the difference between the freezing and boiling points of water is the same on both scales. The conversion between Celsius and absolute temperatures is given by the equation: T(K) = T(°C) + 273.15.
Thermometers
Thermometers are devices used to measure temperature. There are many different types of thermometers, including liquid-in-glass thermometers, thermistors, and thermocouples.
Mercury Thermometer
A mercury thermometer is a type of liquid-in-glass thermometer that uses mercury as the thermometric fluid. As the temperature increases, the mercury expands and rises up the glass tube. Mercury thermometers have largely been replaced by digital thermometers due to safety concerns associated with the toxicity of mercury.
Thermistor
A thermistor is a type of temperature sensor that uses the change in resistance of a material to measure temperature. Thermistors are commonly made from ceramic or polymer materials and are used in applications where high sensitivity is required, such as in electronic circuits.
Thermocouple
A thermocouple is a type of temperature sensor that uses the voltage produced by the junction of two dissimilar metals to measure temperature. Thermocouples are commonly used in industrial applications due to their durability and wide temperature range. They are often made from combinations of metals such as copper, iron, and nickel.
Kinetic Theory of Gases
Elementary Assumptions of the Kinetic Theory
The kinetic theory of gases is a model that explains the behavior of gases at a molecular level. The theory is based on several elementary assumptions:
- Gases consist of a large number of molecules that are in constant random motion.
- The size of the molecules is negligible compared to the average distance between them.
- The molecules collide with each other and with the walls of the container in which the gas is contained.
- The collisions are elastic, meaning that there is no loss of kinetic energy.
- The average kinetic energy of the molecules is proportional to the temperature of the gas.
Expression for Mean Translational Kinetic Energy of Air Molecules
The mean translational kinetic energy of air molecules can be calculated using the following formula:
K = (3/2) kT
Where:
- K is the mean translational kinetic energy of the molecules
- k is Boltzmann's constant (1.38 x 10-23 J/K)
- T is the temperature in Kelvin
This formula shows that the mean translational kinetic energy of the molecules is directly proportional to the temperature of the gas.
Heat Exchange
Heat Capacity
Heat capacity is the amount of heat required to raise the temperature of an object by one degree Celsius. It is given by the formula:
Heat Capacity = Heat Energy / Temperature Change
The SI unit for heat capacity is joules per degree Celsius (J/°C). It is also commonly measured in calories per degree Celsius (cal/°C).
Specific Heat Capacity of Solids and Liquids
The specific heat capacity of a substance is the amount of heat required to raise the temperature of one unit of mass of the substance by one degree Celsius. The specific heat capacity of solids and liquids can be determined by using the following formula:
Specific Heat Capacity = Heat Energy / (Mass x Temperature Change)
The SI unit for specific heat capacity is joules per kilogram per degree Celsius (J/kg/°C) for solids and liquids.
Molar Heat Capacities of Gases
The molar heat capacity of a gas is the amount of heat required to raise the temperature of one mole of the gas by one degree Celsius. The molar heat capacity of a gas at constant volume (Cv) and at constant pressure (Cp) can be determined experimentally.
Determination of Specific Heat Capacities of Solids by the Method of Mixtures
The method of mixtures can be used to determine the specific heat capacity of a solid. This involves mixing a known mass of the solid at a known temperature with a known mass of water at a different temperature, and then measuring the final temperature of the mixture. The specific heat capacity of the solid can then be calculated using the following formula:
Specific Heat Capacity of Solid = (Mass of Water x Specific Heat Capacity of Water x Temperature Change) / (Mass of Solid x Temperature Change)
Newton's Law of Cooling
Newton's law of cooling states that the rate of heat loss of a body is directly proportional to the temperature difference between the body and its surroundings. This can be expressed as:
Rate of Heat Loss = k x Temperature Difference
Where k is the cooling constant, which depends on the properties of the body and the surrounding medium.
Determination of Specific Heat Capacities of a Liquid by the Method of Cooling
The method of cooling can be used to determine the specific heat capacity of a liquid. This involves heating a known mass of the liquid to a known temperature and then allowing it to cool in a calorimeter, which is a device that is designed to minimize heat exchange with the surroundings. The specific heat capacity of the liquid can then be calculated using the following formula: