The world in which we live is incredibly beautiful and full of many different processes that determine the course of life. All these processes are studied by a familiar science - physics. It provides an opportunity to get at least some idea of the origin of the universe. In this article we will consider such a concept as molecular kinetic theory, its equations, types and formulas. However, before proceeding to a deeper study of these issues, it is necessary to clarify for itself the very meaning of physics and the fields it studies.
What is physics?
In fact, this is a very vast science and, perhaps, one of the most fundamental in the history of mankind. For example, if the same computer science is associated with almost every area of human activity, whether it is designing or creating cartoons, then physics is life itself, a description of its complex processes and currents. Let's try to make out its meaning, simplifying the understanding as much as possible.
Thus, physics is a science that studies the energy and matter, the relationships between them, the explanation of many processes taking place in our vast universe. The molecular-kinetic theory of the structure of matter is only a small drop in the sea of theories and branches of physics.
The energy that this science is studying in detail can be represented in a variety of forms. For example, in the form of light, motion, gravity, radiation, electricity and in many other forms. In this article we will touch upon the molecular kinetic theory of the structure of these forms.
The study of matter gives us an idea of the atomic structure of matter. By the way, it follows from the molecular-kinetic theory. The science of the structure of matter allows us to understand and find the meaning of our existence, the causes of the origin of life and the universe itself. Let’s try to study the molecular kinetic theory of matter.
First, some introduction is needed to fully understand the terminology and any conclusions.
Physics Sections
Answering the question of what molecular-kinetic theory is, one cannot help but talk about the branches of physics. Each of these is engaged in a detailed study and explanation of a specific area of human life. They are classified as follows:
- Mechanics, which is divided into two sections: kinematics and dynamics.
- Statics.
- Thermodynamics.
- Molecular section.
- Electrodynamics.
- Optics.
- Physics of quanta and atomic nucleus.
Let's talk specifically about molecular physics, because it is precisely at its core that the molecular kinetic theory is based.
What is thermodynamics?
In general, the molecular part and thermodynamics are closely related branches of physics that study exclusively the macroscopic component of the total number of physical systems. It is worth remembering that these sciences describe exactly the internal state of bodies and substances. For example, their state during heating, crystallization, vaporization and condensation, at the atomic level. In other words, molecular physics is the science of systems that consist of a huge number of particles: atoms and molecules.
It was these sciences that studied the basic principles of molecular kinetic theory.
Even in the seventh grade course, we got acquainted with the concepts of micro- and macrocosms, systems. It will not be superfluous to refresh these terms in memory.
The microworld, as we can see from its very name, consists of elementary particles. In other words, it is a world of small particles. Their sizes are measured in the range from 10 -18 m to 10 -4 m, and the time of their actual state can reach both infinity and disproportionately small intervals, for example, 10 -20 s.
The macrocosm considers bodies and systems of stable forms, consisting of many elementary particles. Such systems are commensurate with our human dimensions.
In addition, there is such a thing as a megaworld. It is made up of a huge planet, space galaxies and complexes.
Theory of the theory
Now that we have repeated a bit and recalled the basic terms of physics, we can proceed directly to the consideration of the main topic of this article.
Molecular-kinetic theory appeared and was formulated for the first time in the nineteenth century. Its essence lies in the fact that it describes in detail the structure of a substance (more often the structure of gases than solid and liquid bodies), based on three fundamental provisions that were compiled from the assumptions of prominent scientists such as Robert Hook, Isaac Newton, Daniel Bernoulli, Mikhail Lomonosov and many others.
The main provisions of the molecular-kinetic theory are as follows:
- Absolutely all substances (regardless of whether they are liquid, solid or gaseous) have a complex structure consisting of smaller particles: molecules and atoms. Atoms are sometimes called "elementary molecules."
- All these elementary particles are always in a state of continuous and chaotic movement. Each of us was faced with direct evidence of this provision, but most likely did not attach any particular importance to this. For example, we all saw against the background of sunlight that dust particles continuously move in a chaotic direction. This is due to the fact that atoms produce mutual shocks with each other, constantly transmitting kinetic energy to each other. This phenomenon was first studied in 1827, and it was named after the discoverer - "Brownian movement".
- All elementary particles are in the process of continuous interaction with each other with certain forces that have electrical rock.
It is worth noting that diffusion serves as another example describing the position at number two, which may also relate, for example, to the molecular kinetic theory of gases. We encounter it in everyday life, and in multiple tests and control tests, so it is important to have an idea about it.
To begin, consider the following examples:
The doctor accidentally spilled alcohol from the flask on the table. Or you dropped a bottle of perfume, and they spread on the floor.
Why, in these two cases, does the smell of alcohol and the smell of perfumes fill the entire room after some time, and not just the area where the contents of these substances spilled?
The answer is simple: diffusion.
Diffusion - what is it? How is it going?
This is a process in which particles that make up one particular substance (usually a gas) penetrate the intermolecular voids of another. In our examples above, the following happened: due to thermal, that is, continuous and disconnected movement, alcohol molecules and / or spirits fell into the gaps between the air molecules. Gradually, under the influence of collisions with atoms and molecules of air, they spread throughout the room. By the way, the intensity of diffusion, that is, its flow rate, depends on the density of the substances involved in the diffusion, as well as on the energy of motion of their atoms and molecules, called kinetic. The greater the kinetic energy, the higher the speed of these molecules, respectively, and the intensity.
The fastest diffusion process can be called diffusion in gases. This is due to the fact that the gas is not homogeneous in composition, which means that intermolecular voids in gases occupy a significant amount of space, respectively, and the process of getting atoms and molecules of foreign matter into them proceeds more simply and faster.
This process takes place a little slower in liquids. Dissolving sugar cubes in a cup with tea is just an example of the diffusion of a solid in a liquid.
But the longest in time is diffusion in bodies with a solid crystalline structure. This is precisely so, because the structure of solids is homogeneous and has a strong crystal lattice, in the cells of which the atoms of the solid matter oscillate. For example, if the surfaces of two metal bars are well cleaned and then made to contact each other, then after a fairly long time we will be able to detect pieces of one metal in the other, and vice versa.
Like any other fundamental section, the basic theory of physics is divided into separate parts: classification, types, formulas, equations, and so on. Thus, we studied the basics of molecular kinetic theory. This means that you can safely proceed to the consideration of individual theoretical blocks.
Molecular kinetic theory of gases
There is a need to understand the provisions of gas theory. As we said earlier, we will consider the macroscopic characteristics of gases, for example, pressure and temperature. This will be needed in the future in order to derive the equation of the molecular kinetic theory of gases. But mathematics - then, and now we will deal with the theory and, accordingly, physics.
Scientists have formulated five principles of the molecular theory of gases, which serve to comprehend the kinetic model of gases. They sound like this:
- All gases are composed of elementary particles that do not have any particular size, but have a certain mass. In other words, the volume of these particles is minimal compared to the length between them.
- Atoms and gas molecules have practically no potential energy, respectively, according to the law, all energy is equal to kinetic.
- We already got acquainted with this position earlier - the Brownian movement. That is, gas particles always perform in a continuous and chaotic motion.
- Absolutely all mutual collisions of gas particles, accompanied by a message of speed and energy, are completely elastic. This means that there are no energy losses or sharp jumps in their kinetic energy in a collision.
- Under normal conditions and a constant temperature, the averaged energy of motion of particles of almost all gases is the same.
The fifth position we can rewrite through this kind of equation of the molecular-kinetic theory of gases:
E = 1/2 * m * v ^ 2 = 3/2 * k * T,
where k is the Boltzmann constant; T is the temperature in Kelvin.
This equation allows us to understand the relationship between the velocity of elementary gas particles and their absolute temperature. Accordingly, the higher their absolute temperature, the greater their speed and kinetic energy.
Gas pressure
Such macroscopic constituent characteristics, such as gas pressure, can also be explained using kinetic theory. For this, we present an example.
Suppose that a molecule of a gas is in a box whose length is L. We will use the above-described provisions of the gas theory and take into account the fact that the molecular sphere moves only along the x-axis. Thus, we can observe the process of elastic collision with one of the walls of the vessel (box).
The momentum of the collision, as we know, is determined by the formula: p = m * v, but in this case this formula will take on the projection form: p = m * v (x).
Since we consider only the dimension of the abscissa axis, that is, the x axis, the total change in momentum will be expressed by the formula: m * v (x) - m * (- v (x)) = 2 * m * v (x).
Next, we consider the force exerted by our object with the help of Newton’s second law: F = m * a = P / t.
From these formulas we express the pressure from the gas side: P = F / a;
Now we substitute the expression of force in the obtained formula and get: P = m * v (x) ^ 2 / L ^ 3.
After that, our ready-made pressure formula can be written for the Nth number of gas molecules. In other words, it will take the following form:
P = N * m * v (x) ^ 2 / V, where v is the velocity and V is the volume.
Now we will try to highlight several basic provisions for gas pressure:
- It manifests itself due to collisions of molecules with the molecules of the walls of the object in which it is located.
- The magnitude of the pressure is directly proportional to the strength and speed of the molecules' impact on the walls of the vessel.
A few brief conclusions on the theory
Before we go further and consider the basic equation of molecular kinetic theory, we offer you some brief conclusions from the above points and theory:
- A measure of the average energy of motion of its atoms and molecules is absolute temperature.
- In the case when two different gases are at the same temperature, their molecules have equal average kinetic energy.
- The energy of gas particles is directly proportional to the root mean square velocity: E = 1/2 / m * v ^ 2.
- Although gas molecules have an average kinetic energy, respectively, and an average speed, individual particles move at different speeds: some fast, some slow.
- The higher the temperature, the higher the speed of the molecules.
- How many times we increase the temperature of the gas (for example, double), so many times the energy of movement of its particles increases (accordingly, doubles).
Basic equation and formulas
The basic equation of molecular kinetic theory allows us to establish the relationship between the values of the microworld and, accordingly, macroscopic, that is, measurable, quantities.
One of the simplest models that molecular theory can consider is the ideal gas model.
We can say that this is a kind of imaginary model studied by the molecular-kinetic theory of an ideal gas, in which:
- the simplest gas particles are considered as perfectly elastic balls, which exhibit interaction both with each other and with the molecules of the walls of any vessel in only one case - absolutely elastic collision;
- there are no attractive forces inside the gas, or they can be neglected;
- elements of the internal structure of the gas can be taken as material points, that is, their volume can also be neglected.
Considering such a model, physicist Rudolf Clausius of German origin wrote the gas pressure formula through the relationship of micro- and macroscopic parameters. It has the form:
p = 1/3 * m (0) * n * v ^ 2.
Later this formula will be called as the main equation of the molecular-kinetic theory of an ideal gas. It can be presented in several different forms. Our responsibility now is to show sections such as molecular physics, molecular kinetic theory, and hence their complete equations and types. Therefore, there is a point in considering other variations of the basic formula.
We know that the average energy characterizing the motion of gas molecules can be found using the formula: E = m (0) * v ^ 2/2.
In this case, we can replace the expression m (0) * v ^ 2 in the original pressure formula with the average kinetic energy. As a result of this, we will have the opportunity to compose the basic equation of the molecular-kinetic theory of gases in this form: p = 2/3 * n * E.
In addition, we know that the expression m (0) * n can be painted as the product of two quotients:
m / N * N / V = m / V = ρ.
After these manipulations, we can rewrite our formula for the equation of the molecular-kinetic theory of an ideal gas in the third, different form, form:
p = 1/3 * ρ * v ^ 2.
Well, perhaps this is all you need to know on this topic. It remains only to systematize the knowledge gained in the form of brief (and not so) conclusions.
All general conclusions and formulas on the subject of "Molecular-kinetic theory"
So let's get started.
Firstly:
Physics is a fundamental science, included in the course of natural science, which is engaged in the study of the properties of matter and energy, their structure, the laws of inorganic nature.
It consists of the following sections:
- mechanics (kinematics and dynamics);
- statics;
- thermodynamics;
- electrodynamics;
- molecular section;
- optics;
- physics of quanta and the atomic nucleus.
Secondly:
Simple particle physics and thermodynamics are closely related sections that study exclusively the macroscopic component of the total number of physical systems, that is, systems consisting of a huge number of elementary particles.
They are based on molecular kinetic theory.
Thirdly:
The essence of the question is as follows. Molecular-kinetic theory describes in detail the structure of a substance (more often the structure of gases than solid and liquid bodies), based on three fundamental positions that were compiled from the assumptions of prominent scientists. Among them: Robert Hook, Isaac Newton, Daniel Bernoulli, Mikhail Lomonosov and many others.
Fourth:
Three main points of molecular kinetic theory:
- All substances (whether they are liquid, solid or gaseous) have a complex structure consisting of smaller particles: molecules and atoms.
- All these simple particles are in a continuous chaotic motion. Example: Brownian motion and diffusion.
- All molecules under any conditions interact with each other with certain forces that have electrical rock.
Each of this thesis of molecular kinetic theory is a solid foundation in the study of the structure of matter.
Fifth:
Several main points of molecular theory for a gas model:
- All gases are composed of elementary particles that do not have any particular size, but have a certain mass. In other words, the volume of these particles is minimal in comparison with the distances between them.
- Atoms and gas molecules have practically no potential energy, respectively, their total energy is equal to kinetic.
- We already got acquainted with this position earlier - the Brownian movement. That is, gas particles are always in continuous and irregular motion.
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p = nkT is the pressure formula through concentration, Boltzmann constant and absolute temperature T. From it follows another fundamental formula, discovered by the Russian scientist Mendeleev and the French physicist-engineer Klaiperon:
pV = m / M * R * T, where R = k * N (a) is the universal constant for gases.
Now we show the constants for different iso-processes: isobaric, isochoric, isothermal and adiabatic.
p * V / T = const - is performed in the case when the mass and composition of the gas are unchanged.
p * V = const - if the temperature is also constant.
V / T = const - if the gas pressure is constant.
p / T = const - if the volume is constant.
Perhaps that’s all you need to know on this topic.
Today we plunged into such a scientific field as theoretical physics, its multiple sections and blocks. In more detail, we touched upon such a field of physics as fundamental molecular physics and thermodynamics, namely, molecular kinetic theory, which, it would seem, does not present any difficulties in the initial study, but actually has many pitfalls. It broadens our understanding of the ideal gas model, which we also studied in detail. In addition, it is worth noting that we got acquainted with the basic equations of molecular theory in their various variations, and also examined all the most necessary formulas for finding certain unknown quantities on this topic. This will be especially useful in preparing for writing any tests, examinations and tests, or to expand the general horizons and knowledge of physics.
We hope that this article was useful to you, and you extracted only the most necessary information from it, strengthening your knowledge in such pillars of thermodynamics as the basic principles of molecular kinetic theory.