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03.05.2017 14:04
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How much does air weigh.
Despite the fact that we cannot see some things that exist in nature, this does not mean at all that they do not exist. It is the same with air - it is invisible, but we breathe it, we feel it, so it is there.
Everything that exists has its own weight. Does the air have it? And if so, how much does air weigh? Let's find out.
When we weigh something (for example, an apple, holding it by a twig), we do it in the air. Therefore, we do not take into account the air itself, since the weight of air in air is zero.
For example, if we take an empty glass bottle and weigh it, we will consider the result obtained as the weight of the flask, without thinking that it is filled with air. However, if we tightly close the bottle and pump out all the air from it, we will get a completely different result. That's it.
Air consists of a combination of several gases: oxygen, nitrogen and others. Gases are very light substances, but they still have weight, although not much.
In order to make sure that the air has weight, ask an adult to help you carry out the following simple experiment: Take a stick about 60 cm long and tie a rope in the middle of it.
Next, attach 2 inflated balloons of the same size to both ends of our stick. And now we will hang our structure by a rope tied to its middle. As a result, we will see that it hangs horizontally.
If we now take a needle and pierce one of the inflated balloons with it, air will come out of it, and the end of the stick to which it was tied will rise up. And if we pierce the second ball, then the ends of the stick will be equal and it will again hang horizontally.
What does it mean? And the fact that the air in the inflated balloon is denser (that is, heavier) than the one that is around it. Therefore, when the ball was blown away, it became lighter.
The weight of the air depends on various factors. For example, air above a horizontal plane is Atmosphere pressure.
Air, as well as all objects that surround us, is subject to gravity. It is this that gives the air its weight, which is equal to 1 kilogram per square centimeter. In this case, the air density is about 1.2 kg / m3, that is, a cube with a side of 1 m, filled with air, weighs 1.2 kg.
An air column rising vertically above the Earth stretches for several hundred kilometers. This means that straight standing man, on his head and shoulders (the area of \u200b\u200bwhich is approximately 250 square centimeters, a column of air weighing about 250 kg presses!
If such a huge weight were not opposed by the same pressure inside our body, we would simply not be able to withstand it and it would crush us. There is another interesting experience that will help you understand everything that we said above:
We take a sheet of paper and stretch it with both hands. Then we will ask someone (for example, a younger sister) to press on it with a finger from one side. What happened? Of course, there was a hole in the paper.
And now we will do the same again, only now it will be necessary to press on the same place with two index fingers, but with different parties. Voila! The paper is intact! Do you want to know why?
Just pressure us sheet of paper on both sides was the same. The same thing happens with the pressure of the air column and the counter pressure inside our body: they are equal.
Thus, we found out that: air has weight and presses it on our body from all sides. However, it cannot crush us, since the counter pressure of our body is equal to the external one, that is, atmospheric pressure.
Our last experiment showed this clearly: if you press on a sheet of paper from one side, it will tear. But if you do it on both sides, this will not happen.
WHAT IS THE DENSITY OF AIR AT 150 DEGREES C (temperature in Celsius), what it is in different units of kg/m3, g/cm3, g/ml, lb/m3. reference TABLE 1.
What is the density of air at 150 degrees Celsius in kg/m3, g/cm3, g/ml, lb/m3 . Do not forget that such a physical quantity, a characteristic of air, as its density in kg / m3 (the mass of a unit volume of atmospheric gas, where 1 m3, 1 cubic meter, 1 cubic meter, 1 cubic centimeter, 1 cm3, 1 milliliter, 1 ml or 1 lb) depends on several parameters. Among the parameters describing the conditions for determining the air density (specific gravity of air gas), I consider the following to be the most important and must be taken into account:
- Temperature air gas.
- Pressure at which the density of the air gas was measured.
- Humidity air gas or the percentage of water in it.
If you are interested in the second case air density at T = 150 degrees C, then excuse me, but I have no desire to copy tabular data, a huge special reference book for air density at various pressures. I cannot yet decide on such a colossal amount of work, and I do not see the need for it. See reference book. Narrow profile information or rare special data, density values, should be sought in primary sources. So smarter.
It is more realistic, and probably more practical from our point of view, to indicate what is the density of air at 150 degrees Celsius, for a situation where the pressure is given by a constant and is atmospheric pressure(under normal conditions - the most popular question). By the way, do you remember what normal atmospheric pressure is? What does it equal? Let me remind you that normal atmospheric pressure is considered to be equal to 760 mm of mercury, or 101325 Pa (101 kPa), in principle, these are normal conditions adjusted for temperature. Meaning, what is the density of air in kg/m3 at a given temperature air gas you will see, find, learn in table 1.
However, it must be said that the values indicated in the table air density values at 150 degrees in kg/m3, g/cm3, g/ml, will not be true for any atmospheric, but only for dry gas. As soon as we change the initial conditions and change the humidity of the air gas, it will immediately have different physical properties. And its density (weight of 1 cubic meter of air in kilograms) at given temperature in degrees C (Celsius) (kg/m3) will also differ from the dry gas density.
Reference table 1. What is the DENSITY OF AIR AT 150 DEGREES CELSIUS (C). HOW MUCH WEIGHS 1 CUBE OF ATMOSPHERIC GAS(weight of 1 m3 in kilograms, weight of 1 cubic meter in kg, weight of 1 cubic meter of gas in g). Density and specific volume of moist air are variables that depend on temperature and air. These values need to be known when selecting fans for, when solving problems related to the movement of a drying agent through air ducts, when determining the power of fan electric motors.This is the mass (weight) of 1 cubic meter of a mixture of air and water vapor at a certain temperature and relative humidity. Specific volume is the volume of air and water vapor per 1 kg of dry air.
Moisture and heat content
The mass in grams per unit mass (1 kg) of dry air in their total volume is called air moisture content. It is obtained by dividing the density of water vapor contained in the air, expressed in grams, by the density of dry air in kilograms.To determine the heat consumption for moisture, you need to know the value heat content of moist air. This value is understood as contained in the mixture of air and water vapor. It is numerically equal to the sum:
DEFINITION
atmospheric air is a mixture of many gases. Air has a complex composition. Its main components can be divided into three groups: constant, variable and random. The former include oxygen (the oxygen content in the air is about 21% by volume), nitrogen (about 86%) and the so-called inert gases (about 1%).
Content constituent parts virtually independent of where the globe a sample of dry air was taken. The second group includes carbon dioxide (0.02 - 0.04%) and water vapor (up to 3%). The content of random components depends on local conditions: near metallurgical plants, noticeable amounts of sulfur dioxide are often mixed into the air, in places where organic residues decay, ammonia, etc. In addition to various gases, air always contains more or less dust.
Air density is a value equal to the mass of gas in the Earth's atmosphere divided by a unit volume. It depends on pressure, temperature and humidity. There is a standard air density value - 1.225 kg / m 3, corresponding to the density of dry air at a temperature of 15 o C and a pressure of 101330 Pa.
Knowing from experience the mass of a liter of air under normal conditions (1.293 g), one can calculate the molecular weight that air would have if it were an individual gas. Since a gram-molecule of any gas occupies under normal conditions a volume of 22.4 liters, the average molecular weight of air is
22.4 × 1.293 = 29.
This number - 29 - should be remembered: knowing it, it is easy to calculate the density of any gas in relation to air.
Density of liquid air
With sufficient cooling, the air becomes liquid. Liquid air can be stored for quite a long time in vessels with double walls, from the space between which air is pumped out to reduce heat transfer. Similar vessels are used, for example, in thermoses.
Freely evaporating under normal conditions, liquid air has a temperature of about (-190 o C). Its composition is unstable, since nitrogen evaporates easier than oxygen. As nitrogen is removed, the color of liquid air changes from bluish to pale blue (the color of liquid oxygen).
In liquid air, ethyl alcohol, diethyl ether and many gases easily turn into a solid state. If, for example, carbon dioxide is passed through liquid air, then it turns into white flakes, similar in appearance to the snow. Mercury immersed in liquid air becomes solid and malleable.
Many substances cooled by liquid air change their properties dramatically. Thus, chink and tin become so brittle that they easily turn into powder, a lead bell makes a clear ringing sound, and a frozen rubber ball shatters if dropped on the floor.
Examples of problem solving
EXAMPLE 1
EXAMPLE 2
| Exercise | Determine how many times heavier than air hydrogen sulfide H 2 S. |
| Solution | The ratio of the mass of a given gas to the mass of another gas taken in the same volume, at the same temperature and the same pressure, is called the relative density of the first gas over the second. This value shows how many times the first gas is heavier or lighter than the second gas. The relative molecular weight of air is taken equal to 29 (taking into account the content of nitrogen, oxygen and other gases in the air). It should be noted that the concept of "relative molecular weight of air" is used conditionally, since air is a mixture of gases. D air (H 2 S) = M r (H 2 S) / M r (air); D air (H 2 S) = 34/29 = 1.17. M r (H 2 S) = 2 × A r (H) + A r (S) = 2 × 1 + 32 = 2 + 32 = 34. |
| Answer | Hydrogen sulfide H 2 S is 1.17 times heavier than air. |
