Why does compression, the temperature rise, why does the temperature increase when compressing gas?

The most direct explanation is that compressing an object means doing work on the object, and the internal energy of the object increases, which is manifested as an increase in temperature. The formula is w = pressure * change in volume. This is especially obvious for gases, where solid liquids are difficult to compress, so the work is small and the temperature change is not obvious.

I've had such a question, please check it out.

Okay, let's not talk about solids and liquids, let's just talk about gases.

The first thing to correct is that the kinetic energy of the molecules of the compressed gas increases, and the potential energy does not change much. Why? In fact, the potential energy between gas molecules is very weak, and there is almost no van der Waals force between them (if there is one, they will combine with each other to form a liquid).

In addition, gases are much less viscous than liquids, which also means that the forces between their molecules are very small.

These are all examples of "weak potential energy", but I think it's best to explain "kinetic energy increase" to convince you. Why does the kinetic energy increase when the gas molecules are compressed? The only way a gas molecule can feel itself compressed is by feeling the container wall approaching it.

When they hit the wall of the container moving inward, the speed at which they come back increases. These molecules that are bounced back quickly transfer their increased energy to the whole gas by means of intermolecular impacts, so that the system is externally realized as an increase in temperature.

If you say, at a certain moment, you wait until the wall of the container has no molecules approaching and immediately squeeze a little in, if there is no impact of the molecules during the squeezing process, then you have achieved the purpose of compressing the volume but not increasing the energy? But know that when no molecules hit the walls of the container, the walls of the container will "feel" that the gas has no pressure at that moment. Is it possible for a container containing gas to not feel the gas pressure at any moment?

Therefore, no matter how the gas is compressed, all the work done will be absorbed by the gas and converted into the kinetic energy of the gas.

If you have any questions, please feel free to follow up.

By: Recreating the Tang Dynasty - Lifting People Level 4 2-25 20:42

There have already been similar problems.

The volume of the compressed gas decreases and the intermolecular impact intensifies, resulting in an increase in average kinetic energy and an increase in temperature.

It can be analyzed from two perspectives:

1. Mechanical energy is converted into heat energy, and there is displacement in the direction of force.

2. The temperature of the gas depends on the movement rate of the gas molecules, when you are not compressed, the gas molecules hit the wall, the rate after ** is unchanged (ideal state), when you compress, the wall and the gas molecules move in the opposite direction, the rate after the collision is increased, and the temperature increases naturally when the rate increases.

Temperature is a macroscopic physical quantity that characterizes the intensity of the thermal motion of a large number of molecules. It is the collective manifestation of the thermal motion of a large number of molecules, like pressure, temperature is also a statistic, for individual molecules, it is meaningless to say how much temperature it has, and the average translational kinetic energy of molecules is proportional to the temperature of the gas, the outside world does work on the gas, in an ideal state, the internal energy of the gas increases, the internal energy of the gas is related to its molecular potential energy and molecular kinetic energy, as the previous comrade said, when doing work on the gas, the potential energy hardly changes, then the main thing is the increase in the kinetic energy of the molecule, In this way, the average translational kinetic energy of the molecules increases, and the temperature of the gas increases.

The work done on the object is converted into internal energy, and temperature is the manifestation of internal energy

Mechanical energy is converted into heat energy.

The higher the temperature, the greater the kinetic energy of the molecules

1. The higher the temperature, the greater the kinetic energy of the molecules, and the more intense the irregular movement of the molecules

2. The more intense the molecular movement, the higher the temperature of the object (which is generally not asked during the exam), which is problematic

The more intense the molecular motion, the more kinetic energy of the molecule increases, and the internal energy of the object increases, but the temperature does not necessarily increase For example, during the melting process of ice, endothermic causes the irregular movement of the molecules to be more intense, but the temperature of the ice remains unchanged

3. Compressing gas, that is, doing work on gas, so that the internal energy of the gas increases and the temperature rises

Formation of irregular movement of molecules:

The irregular motion of molecules is due to the gravitational and repulsive forces of the molecules against each other, and the magnitude and direction of the force experienced by the molecules are constantly changing with time.

For example, a glass of water is a whole, and the irregular movement of molecules in the water does not affect a relatively static state of the water. In other words, the water appears to be stationary in the cup, but the water molecules, which are invisible to the naked eye, are actually in motion. You have to look at the whole, not at the individual molecules.

This proposition is wrong, after the air is compressed, the temperature will rise, the reason is that the compressed air makes the volume of the air smaller, and the compressed air does the work and converts it into the internal energy of the air, so the temperature of the air will rise, which can be popularly understood that the temperature is too late to disperse, so the temperature rises.

The proposition stated below is true, if the outside temperature decreases, the air will compress and the volume will become smaller. The reason is that in the process of temperature drop, the internal and external pressure remains equal, so that the volume becomes smaller, and while the pressure remains the same, the volume is proportional to the temperature. pv=nrt.

Air: The air we breathe every day"Life gases"It is layered on the surface of the earth, transparent and colorless and odorless, it is mainly composed of nitrogen and oxygen, and has an important impact on human survival and production.

Air refers to the mixture of gases in the Earth's atmosphere. It is mainly composed of 78% nitrogen, 21% oxygen, noble gases (helium, neon, argon, krypton, xenon), carbon dioxide, and other substances (such as water vapor, impurities, etc.). The composition of air is not fixed, and as the altitude changes, the air pressure changes, and the proportion of air composition also changes.

But for a long time, it was believed that air was a single substance, until later the French scientist Lavoisier first came to the conclusion that air is composed of oxygen and nitrogen through experiments. At the end of the 19th century, scientists discovered through a large number of experiments that there were rare gases such as helium, argon, and xenon in the air.

In its natural state, the air is tasteless and odorless.

Oxygen in the air is essential for all aerobic organisms. All animals need to breathe oxygen. In addition, plants use carbon dioxide in the air for photosynthesis, which is the only carbon in almost all plants.

When the gas is compressed, the distance between the air molecules decreases, and then the collision between the molecules increases, which generates heat and raises the temperature.

Compressed gases (such as liquid nitrogen) expand in volume when depressurized, and generally speaking, work on the outside world will absorb heat from the outside world.

On the contrary, if you want to compress the gas, you need to do work on the gas, which will release heat to the outside world, such as the gas pipe.

Why compressed air makes the air warmer.

Answer: Compressed air is to do work on the gas, the internal energy of the gas increases, and the performance of the increase in internal energy is the rise of temperature.

Again: Why does compressed air become work?

Again: Just like a balloon, if you don't squeeze it hard, it won't automatically get smaller. When you squeeze it and make it smaller (i.e., compressed), you're doing work on it.

Again: Isn't the work done by an object moving in the direction of the force? How this is also work.

Again: Absolutely.

For another example, suppose the gas is in a cylindrical container, and there is a piston on it (which is the principle of the pump) to press down on the piston, and the gas in the container is compressed. This compression work is easy to calculate, and the direction of force and displacement is the direction of piston motion.

Answer: Pressing down on the piston is to do work on the gas, and pulling up the piston is to do negative work on the gas, or the gas to do work on the piston.

Ask again: So when compressing air, how does the internal energy increase, how does the temperature increase, and how does the work change the internal energy of the molecule, such as how does friction do the work?

Again: The balloon example is essentially the same as the piston, except that the direction and displacement of the force are difficult to determine and are not easy to quantify intuitively.

Again: This is the conservation of energy, when the object is in free fall, the gravitational force does work on the object, the gravitational potential energy is converted into kinetic energy, and the total energy remains unchanged. The same is true for the work done on the gas, the work done on the gas is equal to the increase in the internal energy of the gas, and the total energy remains unchanged.

Answer: Of course, this is the ideal state, but in fact there is also the issue of efficiency, and the transformation of work and energy is not 100%.

Again: What about friction?

Again: Friction is the reason why efficiency is not 100%. Originally, all the work done on the gas should be converted into the internal energy of the gas, but as a result, part of the work done is used to overcome the frictional force.

Again: Of course, friction also generates heat, but it is fundamentally different from compressed gas heat, and the principle is completely different.

Again: So would rubbing your hands be work? Why?

Answer: Of course, the rubbing of both hands also has to overcome the friction to do the work. After all, hands are not absolutely smooth. If there is a displacement of the force and the direction of the force, there is work done (to be precise, mechanical work).

The process of compressing air is the process of doing work on air. Kinetic energy is converted into internal energy, resulting in an increase in the internal energy of the air and an increase in temperature.

The ideal gas of a certain mass follows PV T = constant quantity.

where p is the pressure; v is the volume; t is the temperature.

From the perspective of energy conservation: all the work done by external forces on the gas is used to increase the internal energy of the gas. So compressed air will increase the temperature.

The absolute pressure after compression is divided into the absolute pressure before compression, and then multiplied by the 2nd power, opened to the 7th power, and then multiplied by the temperature before compression, which is the temperature after compression, which is only suitable for dry air environment.

The physical change of the air compression phase: the molecular gap becomes smaller, so the collision is more intense, which is equivalent to the internal work of the air and the internal energy increases.

As for your question, if you compare the relative temperature after compression alone, it will decrease slightly, because in the process of air gap release, the external pressure is greater than the internal pressure, but the overall temperature is rising.

If you are talking about the working principle of the compressor of the air conditioner, it is not the same thing as this, the refrigeration system of the air conditioner has a refrigerant in it, and the high-pressure liquid produced by the refrigerant evaporates and absorbs heat at a low temperature, and at the same time the hot air generated by the compressor is discharged outdoor, and the cold air is blown into the room to achieve the cooling effect.

When compressed, it will be exothermic, because heat is the frequency of molecular vibration, compression reduces the distance, and the speed does not change, so the frequency increases and the temperature increases. Decompression is the opposite.

1.The pressure of the flowing gas is less at the position where the flow velocity is larger, and the pressure is greater at the location where the flow velocity is smaller.

2.There is an ideal gas formula pv=nrt where p is the gas pressure, v is the gas volume, n is the number of gases, r is a constant, and t is the gas temperature.

3.According to the specific analysis of the specific problem, the flow velocity of the air becomes larger and the pressure becomes significantly smaller after passing through the node, v(l)=w(g) (g l), v and n remain unchanged when w is constant, and p decreases t must decrease, where p decreases and t decreases.

This seems to be a bit wrong, compressed air is converted into mechanical energy into internal energy, the volume of air becomes smaller, the pressure increases, and it will be exothermic. After the external force is removed, the compressed gas will return to its original volume and become colder, because the internal energy is smaller than before compression.

Because when the air is compressed, it will release heat.

Heat is absorbed when the pressure returns to normal atmospheric pressure.

So it gets hot when compressed.

The air coming out of the flush compression pump becomes colder.

When compressing gas, the outside world releases energy to the gas inside, and the distance between the molecules becomes smaller, so the collision of molecules is intense, resulting in heat generation and an increase in temperature. (It must be compressed quickly, almost insulated, otherwise the container will transfer heat like the outside, so the temperature will not rise to drip.) )

There is gravitational force and repulsion between molecules, when the gas is not compressed, the molecules are in equilibrium with each other, and their potential energy is the smallest, but after compression, the repulsion force begins to increase, so the potential energy of all molecules in the gas also increases. It's just a very small increase, so you don't have to think about it. So the internal energy becomes greater.

They all have to obey the law of conservation of energy. To add to the example, when the pressure is high to a certain extent (greater than the critical point of repulsion), the state of the object will change, and the gas will be compressed into a liquid.