Thermodynamics
Thermodynamics is a branch of physics that first introduced in the 19th century and is concerned with the study of energy, heat, work, and the transformation of one form of energy into another. The field has its roots in the industrial revolution when scientists and engineers sought to understand and improve the efficiency of steam engines. The development of thermodynamics is closely tied to the work of physicists such as Sadi Carnot, who laid the groundwork for the second law of thermodynamics with his investigations into the efficiency of heat engines.
The laws of thermodynamics were later formulated and refined by scientists like Rudolf Clausius, Lord Kelvin, and others. The applications of thermodynamics are vast and diverse. They include the design and analysis of heat engines, refrigeration systems, chemical processes, and the understanding of phase transitions in materials. Thermodynamics provides a fundamental framework for engineers and scientists to optimize energy systems, design efficient processes, and explore the behavior of matter and energy in various physical and chemical phenomena.
Temperature and Heat:
Temperature:
Temperature measures the average kinetic energy of particles in a substance and is expressed in Kelvin (K) or degrees Celsius (°C) or Fahrenheit (°F). It indicates the hotness or coldness of an object.
Heat:
Heat is the transfer of thermal energy between objects due to a temperature difference. It flows from higher to lower temperatures and can occur through conduction, convection, or radiation. Measured in joules (J), heat is distinct from temperature, representing energy transfer during a temperature change. It is crucial in thermodynamics for understanding energy transformations in physical processes.
Thermometer and its types:
A thermometer is a device used to measure temperature. It typically consists of a temperature-sensing element, such as a liquid, gas, or solid, whose physical properties change with temperature. The \thermometer is calibrated to provide a numerical temperature value corresponding to the observed physical change.
Clinical Thermometer:
It is specifically used for measuring body temperature in medical contexts, a clinical thermometer has a short stem and is calibrated for the human body temperature range. Commonly mercury-based or digital, it offers quick and accurate readings, with digital versions gaining popularity for safety and convenience in healthcare and home use.
Laboratory Thermometer:
It is designed for precision in scientific settings, a laboratory thermometer features a long, narrow glass tube with a calibrated stem, often containing mercury or alcohol. It provides accurate temperature readings over a wide range, suitable for experiments and laboratory applications.
Thermal Expansion:
Thermal expansion refers to the tendency of materials to change their shape, size, or volume in response to changes in temperature. When a substance is heated, its particles gain kinetic energy and vibrate more rapidly, causing the material to expand. Conversely, cooling reduces particle movement, leading to contraction. This phenomenon is pervasive in various materials, including solids, liquids, and gases.
It plays a crucial role in engineering, architecture, and everyday applications. Common examples include the expansion joints in bridges to accommodate temperature variations, the design of bimetallic strips in thermostats, and the accuracy considerations in measuring devices like mercury thermometers, which exploit the expansion of liquids. Thermal expansion is quantified by the coefficient of thermal expansion, which expresses how much a material expands or contracts for each degree change in temperature.
Transfer of Heat:
Heat transfer is the process by which thermal energy is exchanged between regions of different temperatures. There are three main modes of heat transfer:
Conduction:
Conduction is the transfer of heat through a material without any apparent movement of the material itself. In this process, adjacent particles transfer energy through collisions. Good conductors, like metals, allow efficient heat transfer, while insulators, such as rubber or wood, impede heat flow.
Convection:
Convection involves the transfer of heat through the movement of fluids (liquids or gases). When a fluid is heated, it becomes less dense and rises, creating currents that transport heat to other areas. In contrast, cooler fluid descends, completing the convection cycle. Convection is commonly observed in natural phenomena like ocean currents and atmospheric circulation.
Radiation:
Radiation is the transfer of heat through electromagnetic waves. Unlike conduction and convection, radiation does not require a medium to propagate. All objects with a temperature above absolute zero emit thermal radiation. The amount of radiation depends on the temperature and emissivity of the material. This mode of heat transfer is fundamental to processes like solar heating and the cooling of objects through thermal radiation.
Calorimetry:
Calorimetry means measurement of heat. When a body at higher temperature is brought in contact with another body at lower temperature, the heat lost by the hot body is equal to the heat \gained by the colder body, provided no heat is allowed to escape to the surroundings. A device in which heat measurement can be done is called a calorimeter.
It consists of a metallic vessel and stirrer of the same material, like copper or aluminum. The vessel is kept inside a wooden jacket, which contains heat insulating material, like glass wool etc. The outer jacket acts as a heat shield and reduces the heat loss from the inner vessel. There is an opening in the outer jacket through which a mercury thermometer can be inserted into the calorimeter
Ideal Gas Equation and Absolute Temperature:
Ideal Gas Equation:
The ideal gas equation, also known as the ideal gas law, is a fundamental equation in thermodynamics that describes the behavior of an ideal gas. It is an approximation that holds true under certain conditions, such as low pressure and high temperature. The ideal gas equation is expressed as:
P V = n R T
Where, P is the pressure of the gas, V is the volume it occupies, n is the number of moles of the gas, R is the ideal gas constant (a constant with specific units depending on the choice of units for pressure, volume, and temperature) and T is the absolute temperature of the gas measured in kelvins.
Absolute Temperature:
Absolute temperature refers to the temperature measured on the Kelvin scale, denoted by the unit “kelvin” (K). Unlike the Celsius and Fahrenheit scales, which have arbitrary zero points (based on the freezing and boiling points of water under certain conditions), the Kelvin scale starts at absolute zero. Absolute zero is the lowest possible temperature, where the particles of a substance have minimal thermal motion. It is defined as 0 Kelvin, and at this point, theoretically, no more heat can be removed from the substance.
Change of State and Triple Point:
Change of State:
Change of state refers to the transition of matter from one physical state to another, such as from a solid to a liquid (melting), liquid to gas (vaporization), or gas to liquid (condensation). These changes occur due to alterations in temperature and pressure. The three primary states of matter solid, liquid, and gas can interconvert through the absorption or release of heat energy.
Triple Point:
The triple point is a specific set of conditions at which all three phases of a substance—solid, liquid, and gas—coexist in thermodynamic equilibrium. At the triple point, the substance exists simultaneously as a solid, liquid, and gas, and any change in temperature, pressure, or composition would cause a phase transition. The triple point provides a precise reference point for defining the Kelvin temperature scale. For water, the triple point is defined to be exactly 273.16 kelvins (0.01°C) and 611.657 pascals (6.11657 m bar) of pressure.
Specific Heat Capacity:
Specific heat capacity, often referred to simply as specific heat, is a thermodynamic property that quantifies the amount of heat energy required to raise the temperature of a unit mass of a substance by one degree Celsius (or one kelvin). It is denoted by the symbol cc and is expressed in units of joules per kilogram per degree Celsius (J/(kg⋅°C)).
The formula for specific heat (c) is given by:
Q = m c ΔT
Where, Q is the heat energy absorbed or released, m is the mass of the substance, C is the specific heat capacity and ΔT is the change in temperature.
Thermal Equilibrium:
Thermal equilibrium is a state in which two or more objects or systems, in thermal contact with each other, have the same temperature, and there is no net flow of heat between them. In this state, the rates of heat transfer between the systems are equal and opposite, resulting in zero net heat flow.
This concept is fundamental in thermodynamics and is related to the zeroth law, stating that if two systems are each in thermal equilibrium with a third, they are in thermal equilibrium with each other. Thermal equilibrium is crucial in temperature measurements and the study of heat transfer processes, serving as the foundation for temperature scales and playing a central role in the understanding of energy behavior in systems.
Laws of Thermodynamics:
Zeroth Law of Thermodynamics:
The zeroth law establishes the concept of temperature and thermal equilibrium. It states that if two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other. This law forms the basis for temperature measurement and the construction of temperature scales.
First Law of Thermodynamics:
The first law states that energy cannot be created or destroyed in an isolated system; it can only change forms. This law is often expressed as the principle of conservation of energy. It introduces the concept of internal energy, heat transfer, and work done in a system. Mathematically, it can be stated as ΔU = Q − W, where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system.
Second Law of Thermodynamics:
The second law introduces the concept of entropy, a measure of the disorder or randomness in a system. It states that in any energy transfer or transformation, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state. This law leads to the idea of the direction of natural processes, emphasizing that systems tend to move toward states of higher entropy. The second law also introduces the concept of heat engines and their efficiency, stating that no heat engine can be 100% efficient in converting heat into work.
Thermodynamic Process:
A thermodynamic process refers to the transformation of a system from one state to another, involving changes in thermodynamic variables such as temperature, pressure, volume, and internal energy. These processes are fundamental concepts in thermodynamics and are often represented on thermodynamic diagrams, such as pressure-volume (PV) or temperature-entropy (TS) diagrams. Several types of thermodynamic processes are commonly encountered:
Quasi-Static Process
A quasi-static process is an infinitely slow process such that the system remains in thermal and mechanical equilibrium with the surroundings throughout. In a quasi-static process, the pressure and temperature of the environment can differ from those of the system only infinitesimally
Isothermal Process:
An isothermal process occurs at constant temperature. For such a process, the internal energy change is related only to work done and heat absorbed or released.
Adiabatic Process:
An adiabatic process involves no heat exchange with the surroundings. The change in internal energy is solely due to work done on or by the system.
Isobaric Process:
An isobaric process occurs at constant pressure. The work done in this process is given by the product of pressure and the change in volume.
Isochoric (Isometric) Process:
An isochoric process takes place at constant volume. Since there is no change in volume, the work done is zero, and the heat added or removed is equal to the change in internal energy.
Cyclic Process:
A cyclic process is one in which the system returns to its initial state after a series of changes. The net work done and heat exchanged over the entire cycle is typically of interest.
Newton’s Law of Cooling
Newton’s Law of Cooling is a mathematical expression describing the rate at which the temperature of an object changes as it interacts with its surroundings. It was formulated by Sir Isaac Newton and is particularly applicable to the cooling of objects in a medium, such as air or water. The law states that the rate of change of the temperature of an object is directly proportional to the difference between its own temperature and the ambient temperature. Mathematically, it can be expressed as:
(dT / dt) = -k ⋅ ( T − Ta)
Where, (dT / dt) is the rate of change of temperature with respect to time, T is the temperature of the object, Ta is the ambient temperature (temperature of the surroundings), k is a positive constant and The negative sign indicates that the temperature decreases as T approaches Ta.
The solution to this first-order ordinary differential equation is given by:
T(t) = Ta + ( T0 – Ta ) ⋅ e-kt
Where, T(t) is the temperature at time t and T0 is the initial temperature of the object
Reversible and Irreversible Processes:
Reversible and irreversible processes are concepts in thermodynamics that describe the nature of changes a system undergoes. These terms are used to characterize the directionality and efficiency of energy transfers and transformations.
Reversible Process:
In a reversible process, a system undergoes changes in such a way that it can be returned to its initial state by an infinitesimally small change in some external condition, without leaving any effect on the surroundings. Reversible processes are idealizations and serve as a useful theoretical concept. In reality, achieving perfect reversibility is often not possible due to factors like friction, heat dissipation, and other forms of irreversibility.
Irreversible Process:
An irreversible process is one in which the system undergoes changes that cannot be undone, and there is an inevitable loss of energy to the surroundings. Irreversible processes are characterized by the production of entropy, and they are associated with real-world phenomena such as friction, heat conduction, and irreversibilities in mechanical and thermal processes. Common examples include the expansion of a gas into a vacuum and the mixing of two substances.
Conclusion:
In conclusion, Thermodynamics, a pivotal branch of physics, explores energy transfer and transformations. The zeroth law introduces temperature and thermal equilibrium. The first law emphasizes energy conservation, and the second law introduces entropy, giving directionality to processes. Thermodynamic processes, reversible or irreversible, are key for understanding matter behavior. The third law addresses systems near absolute zero. Applied extensively, thermodynamics guides the design of energy systems, studies chemical reactions, and shapes technological advancements.