Physics is the study of nature's fundamental laws and how they reflect themselves in diverse natural phenomena. It is the combined study of the macrostructural and microstructural aspects of the matter. From a microscopic viewpoint, the behavior of matter is studied by adding up the behaviors of individual molecules. On the contrary, from a macroscopic perspective, we deal with the matter in terms of some specified quantities like pressure, volume, temperature, mass, etc. The majority of a substance's macroscopic properties are determined by how the constituent particles are arranged and held together. Thermodynamics falls into the macroscopic domain of physics.
The branch of physics that deals with heat and energy concepts, including the conversion of heat to other forms of energy is called Thermodynamics. It describes the interaction of heat, work, temperature, and energy. It is concerned with bulk systems and the transfer of energy from one place to another, as well as from one form to another. In thermodynamics, four laws have been described: the zeroth law, the first law, the second law, the third law, and the fourth law. The last three laws, namely the first, second, and third laws, have been named in the order in which they were discovered. The zeroth law was established following the first three laws, and it is a more basic statement that serves as the foundation for the definition of temperature, hence the name. Below is a detail description to the first law of thermodynamics, also known as the "law of conservation of energy."
What is the first law of Thermodynamics?
The first and second laws of thermodynamics were developed around 1850 by Rudolf Clausius and William Thomson (Kelvin).
The first law of thermodynamics is a generalized statement of energy conservation. The law of conservation of energy states that the total energy of an isolated system remains constant, i.e., it can neither be created nor destroyed, but can be transferred from one system to another. It establishes heat as a form of energy and introduces the concept of internal energy. The law states that “total heat energy given to a system is converted into internal energy and work done on the system.” It can mathematically be stated as:
∆Q = ∆U + W
Where ∆Q is the total energy given to the system, ∆U is the change in internal energy and W is the work done.
The reason why the first law is called the law of conservation of energy is that it attempts to explain how to get more energy as a outcome in comparison to the energy supplied. This can be associated with the terms of heat and motion. Whenever heat is released or absorbed, it always takes energy with it. This could be the heat from an oven, a hot spring in Japan, or the heat from the Sun. This can also be noticed in machines - whenever you run a machine, whether that's a fan, a drill, or a spinning wheel, you are always doing so by converting energy from one form to another.
To calculate the change in internal energy, this equation can be rearranged as:
∆U = ∆Q - W
Sign Conventions:
Heat: Heat transfer into a system is positive, whereas heat transfer out of a system is negative. Heat transfer that increases the energy of a system is considered positive, while heat transfer that causes a decrease in the energy of a system is considered negative.
Work: Work performed by a system is positive, while work performed on a system is negative.
Internal Energy, Heat, and work: A brief outline
Internal Energy: Any massive system that you consider is made up of molecules. These molecules possess a certain amount of energy. This summation of the total energy of these molecules, i.e., the total kinetic and potential energy of this system, is referred to as its internal energy. It is a macroscopic variable of a system and is an example of a "state variable" in thermodynamics, i.e., its value depends only on the state of the system, irrespective of the path taken to achieve that state.
Heat: Heat is energy in motion. It does not represent the energy of the system, but rather the external energy that is applied that brings about the change in the internal energy of the system. When any amount of heat is applied to a system, a certain amount of it is lost in changing the internal energy of the system, and another is lost in the work done by the system.
Work: The amount of energy transferred from one system to another is referred to as Thermodynamic work. Work done can be expressed as force times displacement. Since force can be represented as pressure times area and area multiplied by displacements equals volume, we can derive a different expression for the equation of the first law:
∆Q = ∆U + P ∆V
Where P represents constant pressure and ∆V is the volume change.
The First Law of Thermodynamics Is Important
The first law of thermodynamics is based on the concept of energy conservation. This means that energy cannot be created or destroyed, but it can change forms with no loss of energy. The nature of the process affects both dQ and do when a system transitions from one state to another. dU, on the other hand, is constant across all operations. It confirms that the total energy of the universe remains constant, under all circumstances.
Limitations of First Law
The first law of thermodynamics is not universal because it has a few exceptions.
It does not say anything about the direction in which heat flows.
It also doesn't specify whether the process is spontaneous or not.
Additionally, it does not provide evidence for any changes to state that may occur during this change such as pressure drops when gas molecules collide with each other at high velocities.
It does not reveal the final temperature of two bodies in direct contact.
It does not provide any information about the system's entropy.
Thermodynamic systems
There are three types of thermodynamic systems that have been mentioned. These are:
Open System: An open thermodynamic system is one in which energy and matter are constantly exchanged with the outside world. In an open system, mass varies. Here are some examples of open systems: Using a piston-cylinder arrangement with no valves, a lid is placed on the saucepan.
Closed System: In a closed system, only energy can be exchanged with the environment. The mass remains constant in such systems. An open saucepan serves as an example of an open system.
Isolated System: An isolated system does not exchange energy or matter with its surroundings. A thermos flask is an example. The concept of an isolated system, on the other hand, is entirely fictitious.
Thermodynamic processes
The movement of heat energy within or between systems is referred to as thermodynamic processes. There are several paths that a thermodynamic system can take from its initial state to its final state. These paths are related to thermodynamic processes.
The following four thermodynamic processes can be described:
Isothermal process: An isothermal process produces no temperature change, implying that the temperature remains constant.
Isobaric process: Isobaric thermodynamic processes are those in which the pressure of the system remains constant.
Isochoric process: An isochoric process is one in which the volume of the system remains constant. The isochoric process is illustrated by the heating of a gas in a closed cylinder.
Adiabatic process: An adiabatic process is one in which the heat content of the system remains constant. Heat can neither enters nor exits the system during this process.
Quasi-static process: A quasi-static process is infinitely slow and maintains thermal and mechanical equilibrium with its surroundings throughout. The pressure and temperature of the environment can only be infinitesimally different from those of the system in a quasi-static process.
First Law for open systems
In contrast to a closed system, mass flows into and out of an open system. Mass conservation should be considered in this case.
A system is closed if it can’t exchange energy, matter, or heat with its surroundings. A sealed box, for example, is a closed system.
The first law of thermodynamics explains why open systems naturally tend to run hotter than closed ones. When an open system absorbs heat, it can either release it as waste heat or it can transfer it to its surroundings. If the system doesn’t release the heat, then it is naturally going to get hotter.
Applications of the first law
A few typical examples of the first law of thermodynamics are:
Heat Engine: The heat engine is the most common practical application of the First Law. Heat engines convert thermal energy to mechanical energy and vice versa. A heat engine is a device in which a system goes through a cyclic process that converts heat into work. Open systems comprise the vast majority of heat engines. The basic concept of a heat engine is based on the relationships between heat, volume, and pressure of a working fluid. This fluid is normally a gas, but in some cases, it may transition from gas to liquid and back to gas during a cycle.
Refrigerator, Air conditioner, and heat pump: A refrigerator works in the opposite direction of a heat engine. Refrigerators and heat pumps are mechanical energy converters that convert mechanical energy to thermal energy. Closed systems account for the vast majority of these. The working fluid is sent outside by a mechanical pump, where it is compressed and heated. A reverse-cycle air conditioner is simply referred to as a heat pump.
Some natural examples of the first law of thermodynamics are Photosynthesis and Metabolism. In photosynthesis, Solar energy is absorbed by the leaves of a green plant as it reaches the earth. In the process known as photosynthesis, individual cells in the leaves use solar energy to convert carbon dioxide and water into carbohydrates. Solar energy is transformed into chemical energy, which is stored in carbohydrate molecules.
The incandescent light bulb is a well-known example of the law of conservation of energy. When a thin wire within the bulb is heated until it glows, light is created. In the wire, electrical energy is turned into both heat and light energy.
Summary
Thermodynamics is the study of heat and energy. It's used to explain why some systems naturally tend to run hotter or colder than others. It also explains why some systems naturally tend to stay the same while others naturally tend to change over time. The laws of thermodynamics are the fundamental principles that govern the physics of heat and thermal energy. The laws are based on the concept that energy is neither created nor destroyed, but can be transferred between different forms.
The First Law of Thermodynamics explains why open systems naturally tend to run hotter than closed ones. Closed systems naturally tend to run colder than open ones. It states that energy can be neither created nor destroyed - only changed from one form to another. This means that the universe's total amount of energy remains constant. The only way that energy can change is if it is converted from one form to another.