1.1 Temperature and Thermal Equilibrium
3 min read•june 24, 2024
and are key concepts in thermodynamics. They help us understand how heat moves between objects and why things reach the same when left in contact for a while.
These ideas explain everyday experiences, like why your hot coffee cools down or how a fever works. They also form the basis for more complex thermal systems and energy transfer processes in physics and engineering.
Temperature and Thermal Equilibrium
Temperature in everyday life and science
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- Measures the average of particles in a system
- Higher temperature means higher average kinetic energy (hot coffee)
- Lower temperature means lower average kinetic energy (iced tea)
- Everyday examples demonstrate temperature differences
- A person with a fever has higher body temperature than a healthy person
- A hot stove burner has higher temperature than a room-temperature countertop
- Scientific concepts define temperature scales and limits
- is the lowest possible temperature with minimal particle kinetic energy
- is an with 0 K at
- and scales are relative based on specific reference points (freezing and boiling points of water)
Process of thermal equilibrium
- Occurs when two or more systems in reach the same temperature
- No net between systems in
- Heat always flows from higher-temperature to lower-temperature objects
- Continues until both objects reach the same temperature and achieve thermal equilibrium
- Rate of heat transfer depends on several factors
- Temperature difference between the objects
- Surface area of contact
- Material properties like
- Examples demonstrate thermal equilibrium in action
- A hot metal spoon in cold water eventually reaches water temperature
- A room-temperature object in a refrigerator cools down to match interior temperature
- occurs as objects reach thermal equilibrium, affecting their size and shape
Zeroth law for temperature predictions
- States that if two systems are in thermal equilibrium with a third system, they are also in thermal equilibrium with each other
- If A and C are in thermal equilibrium, and B and C are in thermal equilibrium, then A and B are in thermal equilibrium
- Allows for the concept of temperature and the use of thermometers
- A thermometer reaches thermal equilibrium with the system it measures
- Predicts temperature changes in interacting systems
- Heat flows from higher-temperature to lower-temperature objects in thermal contact
- Final system temperature will be between the initial temperatures of the two objects
- Specific final temperature depends on heat capacities and masses of the objects
- Applies the zeroth law to real-world situations
- A room-temperature thermometer in a hot liquid initially reads lower than the liquid but eventually reaches thermal equilibrium and displays liquid temperature
- Mixing hot and cold water results in a final mixture temperature between the initial temperatures, depending on their relative volumes and temperatures
Heat and Energy in Thermal Systems
- represents the total kinetic energy of particles in a system
- capacity determines how much thermal energy a material can store per unit mass and temperature change
- is the energy absorbed or released during phase changes without temperature change
- occurs when a system is in thermal, mechanical, and chemical equilibrium simultaneously
Key Terms to Review (32)
Absolute temperature scale: An absolute temperature scale is a thermodynamic temperature scale that uses absolute zero as its null point. The two most common absolute temperature scales are Kelvin and Rankine.
Absolute zero: Absolute zero is the lowest possible temperature where all molecular motion ceases. It is 0 Kelvin, or -273.15 degrees Celsius.
Absolute Zero: Absolute zero is the lowest possible temperature, at which the motion of atoms and molecules comes to a complete stop. It is the point at which a system reaches its minimum energy state, and is the coldest possible temperature that can be achieved in the physical universe.
Celsius: Celsius is a temperature scale that measures the degree of hotness or coldness of an object or environment. It is based on the freezing and boiling points of water, with 0°C representing the freezing point and 100°C representing the boiling point of water at standard atmospheric pressure.
Constant-volume gas thermometer: A constant-volume gas thermometer measures temperature by observing the pressure of a gas held at constant volume. The relationship between pressure and temperature is governed by the ideal gas law.
Degree Celsius: The degree Celsius (°C) is a unit of temperature on the Celsius scale, where 0°C is the freezing point of water and 100°C is its boiling point at standard atmospheric pressure. It is used widely in most scientific contexts for measuring temperature.
Degree Fahrenheit: Degree Fahrenheit is a unit of temperature measurement in the imperial system, primarily used in the United States. It is based on a scale where the freezing point of water is 32 degrees and the boiling point is 212 degrees under standard atmospheric conditions.
Fahrenheit: Fahrenheit is a temperature scale that measures temperature in degrees Fahrenheit (°F). It is commonly used in the United States and a few other countries, and is based on the freezing and boiling points of water under standard atmospheric pressure.
Heat Capacity: Heat capacity is a physical property that describes the amount of heat required to raise the temperature of a substance by a certain amount. It represents the material's ability to store thermal energy and is an important concept in understanding heat transfer, thermodynamics, and the behavior of materials under different temperature conditions.
Heat transfer: Heat transfer is the process of thermal energy moving from a region of higher temperature to a region of lower temperature. It occurs through conduction, convection, and radiation.
Isothermal expansion: Isothermal expansion is a thermodynamic process in which a gas expands at a constant temperature. During this process, the internal energy of the gas remains unchanged while work is done by the gas.
Kelvin: Kelvin is the base unit of temperature in the International System of Units (SI), named after the physicist William Thomson, Lord Kelvin. It is a fundamental unit that is used to measure the absolute temperature of a system, providing a scale that is independent of the properties of any particular substance.
Kelvin scale: The Kelvin scale is an absolute temperature scale starting at absolute zero, the point where all molecular motion ceases. It is used in scientific measurements and calculations due to its direct relationship with thermal energy.
Kinetic Energy: Kinetic energy is the energy of motion possessed by an object due to its movement. It is the energy that an object has by virtue of being in motion and is directly proportional to the mass of the object and the square of its velocity.
Latent Heat: Latent heat refers to the energy released or absorbed by a substance during a phase change, such as the transition from a solid to a liquid or from a liquid to a gas, without a change in temperature. It is the energy required to change the state of a substance without altering its temperature.
Latent heat coefficient: The latent heat coefficient is the amount of heat energy required to change the phase of a unit mass of a substance without changing its temperature. It is typically measured in units of J/kg.
Molar heat capacity at constant volume: Molar heat capacity at constant volume ($C_V$) is the amount of heat required to raise the temperature of one mole of a substance by 1 degree Celsius at constant volume. It is a key parameter in understanding the thermodynamic properties of gases.
Specific heat: Specific heat is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius. It is a material-specific property and is measured in units of $\text{J/g} \cdot ^\circ \text{C}$.
Specific Heat: Specific heat, also known as specific heat capacity, is a measure of the amount of energy required to raise the temperature of a substance by one degree. It is a fundamental property that describes how much heat a material can absorb or release per unit mass and per unit temperature change.
Temperature: Temperature is a measure of the average kinetic energy of the particles in a substance. It determines the direction of heat transfer between objects.
Temperature: Temperature is a measure of the average kinetic energy of the particles (atoms or molecules) in a substance. It quantifies the degree of hotness or coldness of an object and is a fundamental concept in thermodynamics that is closely related to the transfer of heat energy.
Thermal conductivity: Thermal conductivity is a material's ability to conduct heat. It quantifies the rate at which heat energy passes through a material given a temperature gradient.
Thermal Conductivity: Thermal conductivity is a material property that describes the ability of a substance to transfer heat. It is a measure of how quickly heat can flow through a material, and it is a crucial factor in understanding heat transfer processes.
Thermal Contact: Thermal contact refers to the physical interaction between two objects or systems that allows the transfer of thermal energy, or heat, from one to the other. This concept is fundamental in understanding temperature and thermal equilibrium, as it governs how heat flows between objects and how they reach a state of equilibrium.
Thermal Energy: Thermal energy is the total kinetic energy of the random motion of the particles (atoms and molecules) within a substance. It is a form of internal energy that is directly related to the temperature of a material and the heat transfer processes that occur within it.
Thermal equilibrium: Thermal equilibrium is the state in which two or more objects in thermal contact no longer exchange heat, resulting in a uniform temperature throughout the system. This occurs when the temperatures of the objects are equal.
Thermal Equilibrium: Thermal equilibrium is a state in which two or more objects or systems have reached the same temperature and no longer exchange heat energy. This concept is fundamental to understanding temperature, thermometers, heat transfer, and the behavior of thermodynamic systems.
Thermal Expansion: Thermal expansion is the phenomenon where the size or volume of an object increases as its temperature rises. This occurs because the atoms or molecules within the object vibrate more and occupy a larger space as they gain kinetic energy from the increased temperature.
Thermodynamic Equilibrium: Thermodynamic equilibrium is a state in which the macroscopic properties of a system, such as temperature, pressure, and chemical composition, do not change over time. It is a fundamental concept in thermodynamics that underpins the study of energy transformations, work, heat, and the behavior of systems.
Thermometer: A thermometer is a device used to measure and indicate the temperature of a substance or environment. It is a fundamental tool in the study of temperature and thermal equilibrium, heat transfer, and mechanisms of heat transfer.
Zeroth law of thermodynamics: The zeroth law of thermodynamics states that if two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. This law forms the basis for the concept of temperature.
Zeroth Law of Thermodynamics: The zeroth law of thermodynamics states that if two systems are in thermal equilibrium with a third system, then they are also in thermal equilibrium with each other. This law establishes the concept of temperature and provides the basis for temperature measurement.