How much does 1 cubic meter of air weigh. How much does air weigh. Determining the weight of air under given conditions
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).Air density is a physical quantity that characterizes the specific mass of air under natural conditions or the mass of gas in the Earth's atmosphere per unit volume. The value of air density is a function of the height of the measurements, its humidity and temperature.
A value equal to 1.29 kg/m3 is taken as the air density standard, which is calculated as the ratio of its molar mass (29 g/mol) to the molar volume, which is the same for all gases (22.413996 dm3), corresponding to the density of dry air at 0° C (273.15 °K) and a pressure of 760 mmHg (101325 Pa) at sea level (that is, under normal conditions).
Not so long ago, information about air density was obtained indirectly through observations of auroras, the propagation of radio waves, and meteors. Since the advent of artificial Earth satellites, air density has been calculated thanks to data obtained from their deceleration.
Another method is to observe the spreading of artificial clouds of sodium vapor created by meteorological rockets. In Europe, the air density at the Earth's surface is 1.258 kg/m3, at an altitude of five km - 0.735, at an altitude of twenty km - 0.087, at an altitude of forty km - 0.004 kg/m3.
There are two types of air density: mass and weight (specific gravity).
The weight density determines the weight of 1 m3 of air and is calculated by the formula γ = G/V, where γ is the weight density, kgf/m3; G is the weight of air, measured in kgf; V is the volume of air, measured in m3. Determined that 1 m3 of air under standard conditions(barometric pressure 760 mmHg, t=15°C) weighs 1.225 kgf, based on this, the weight density (specific gravity) of 1 m3 of air is equal to γ = 1.225 kgf/m3.
It should be taken into account that the weight of air is a variable and varies depending on various conditions, such as geographical latitude and the force of inertia that occurs when the Earth rotates around its axis. At the poles, the weight of air is 5% more than at the equator.
The mass density of air is the mass of 1 m3 of air, denoted by the Greek letter ρ. As you know, body weight is a constant value. A unit of mass is considered to be the mass of a weight made of platinum iridide, which is located in the International Chamber of Weights and Measures in Paris.
Air mass density ρ is calculated using the following formula: ρ = m / v. Here m is the mass of air, measured in kg×s2/m; ρ is its mass density, measured in kgf×s2/m4.
The mass and weight density of air are dependent: ρ = γ / g, where g is the free fall acceleration coefficient equal to 9.8 m/s². Whence it follows that the mass density of air under standard conditions is 0.1250 kg×s2/m4.
As barometric pressure and temperature change, air density changes. Based on the Boyle-Mariotte law, the greater the pressure, the greater will be the density of the air. However, as the pressure decreases with height, the air density also decreases, which introduces its own adjustments, as a result of which the law of vertical pressure change becomes more complicated.
The equation that expresses this law of change in pressure with height in an atmosphere at rest is called basic equation of statics.
It says that with increasing altitude, the pressure changes downwards and when ascending to the same height, the decrease in pressure is the greater, the greater the force of gravity and air density.
An important role in this equation belongs to changes in air density. As a result, we can say that the higher you climb, the less pressure will drop when you rise to the same height. The density of air depends on temperature as follows: in warm air, the pressure decreases less intensively than in cold air, therefore, at the same height in a warm air mass, the pressure is higher than in cold air.
With changing values of temperature and pressure, the mass density of air is calculated by the formula: ρ = 0.0473xV / T. Here B is the barometric pressure, measured in mm of mercury, T is the air temperature, measured in Kelvin.
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Density is also determined by air humidity. The presence of water pores leads to a decrease in air density, which is explained by the low molar mass of water (18 g/mol) against the background of the molar mass of dry air (29 g/mol). Humid air can be considered as a mixture of ideal gases, in each of which the combination of densities allows one to obtain the required density value for their mixture.
Such a kind of interpretation allows density values to be determined with an error level of less than 0.2% in the temperature range from −10 °C to 50 °C. The density of air allows you to get the value of its moisture content, which is calculated by dividing the density of water vapor (in grams), which is contained in the air, by the density of dry air in kilograms.
The basic equation of statics does not allow solving constantly emerging practical problems in real conditions of a changing atmosphere. Therefore, it is solved under various simplified assumptions that correspond to the actual real conditions, by putting forward a number of particular assumptions.
The basic equation of statics makes it possible to obtain the value of the vertical pressure gradient, which expresses the change in pressure during ascent or descent per unit height, i.e., the change in pressure per unit vertical distance.
Instead of the vertical gradient, the reciprocal of it is often used - the baric step in meters per millibar (sometimes there is still an outdated version of the term "pressure gradient" - the barometric gradient).
The low air density determines a slight resistance to movement. Many terrestrial animals, in the course of evolution, used the ecological benefits of this property of the air environment, due to which they acquired the ability to fly. 75% of all land animal species are capable of active flight. For the most part, these are insects and birds, but there are mammals and reptiles.
Video on the topic "Determination of air density"
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%).
The content of constituents practically does not depend on where in the world the 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, it turns into white flakes, similar in appearance to 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. |
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 atmospheric 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 on a standing person, 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 thing again, only now it will be necessary to press on the same place with two index fingers, but from different sides. 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.
The main physical properties of air are considered: air density, its dynamic and kinematic viscosity, specific heat capacity, thermal conductivity, thermal diffusivity, Prandtl number and entropy. The properties of air are given in tables depending on the temperature at normal atmospheric pressure.
Air density versus temperature
A detailed table of dry air density values at various temperatures and normal atmospheric pressure is presented. What is the density of air? The density of air can be analytically determined by dividing its mass by the volume it occupies. under given conditions (pressure, temperature and humidity). It is also possible to calculate its density using the ideal gas equation of state formula. To do this, you need to know the absolute pressure and temperature of the air, as well as its gas constant and molar volume. This equation allows you to calculate the density of air in a dry state.
On practice, to find out what is the density of air at different temperatures, it is convenient to use ready-made tables. For example, the given table of atmospheric air density values depending on its temperature. The air density in the table is expressed in kilograms per cubic meter and is given in the temperature range from minus 50 to 1200 degrees Celsius at normal atmospheric pressure (101325 Pa).
| t, °С | ρ, kg / m 3 | t, °С | ρ, kg / m 3 | t, °С | ρ, kg / m 3 | t, °С | ρ, kg / m 3 |
|---|---|---|---|---|---|---|---|
| -50 | 1,584 | 20 | 1,205 | 150 | 0,835 | 600 | 0,404 |
| -45 | 1,549 | 30 | 1,165 | 160 | 0,815 | 650 | 0,383 |
| -40 | 1,515 | 40 | 1,128 | 170 | 0,797 | 700 | 0,362 |
| -35 | 1,484 | 50 | 1,093 | 180 | 0,779 | 750 | 0,346 |
| -30 | 1,453 | 60 | 1,06 | 190 | 0,763 | 800 | 0,329 |
| -25 | 1,424 | 70 | 1,029 | 200 | 0,746 | 850 | 0,315 |
| -20 | 1,395 | 80 | 1 | 250 | 0,674 | 900 | 0,301 |
| -15 | 1,369 | 90 | 0,972 | 300 | 0,615 | 950 | 0,289 |
| -10 | 1,342 | 100 | 0,946 | 350 | 0,566 | 1000 | 0,277 |
| -5 | 1,318 | 110 | 0,922 | 400 | 0,524 | 1050 | 0,267 |
| 0 | 1,293 | 120 | 0,898 | 450 | 0,49 | 1100 | 0,257 |
| 10 | 1,247 | 130 | 0,876 | 500 | 0,456 | 1150 | 0,248 |
| 15 | 1,226 | 140 | 0,854 | 550 | 0,43 | 1200 | 0,239 |
At 25°C, air has a density of 1.185 kg/m 3 . When heated, the density of air decreases - the air expands (its specific volume increases). With an increase in temperature, for example, up to 1200°C, a very low air density is achieved, equal to 0.239 kg/m 3 , which is 5 times less than its value at room temperature. In general, the decrease in heating allows a process such as natural convection to take place and is used, for example, in aeronautics.
If we compare the density of air with respect to, then air is lighter by three orders of magnitude - at a temperature of 4 ° C, the density of water is 1000 kg / m 3, and the density of air is 1.27 kg / m 3. It is also necessary to note the value of air density under normal conditions. Normal conditions for gases are those under which their temperature is 0 ° C, and the pressure is equal to normal atmospheric pressure. Thus, according to the table, air density under normal conditions (at NU) is 1.293 kg / m 3.
Dynamic and kinematic viscosity of air at different temperatures
When performing thermal calculations, it is necessary to know the value of air viscosity (viscosity coefficient) at different temperatures. This value is required to calculate the Reynolds, Grashof, Rayleigh numbers, the values of which determine the flow regime of this gas. The table shows the values of the coefficients of dynamic μ and kinematic ν air viscosity in the temperature range from -50 to 1200°C at atmospheric pressure.
The viscosity of air increases significantly with increasing temperature. For example, the kinematic viscosity of air is 15.06 10 -6 m 2 / s at a temperature of 20 ° C, and with an increase in temperature to 1200 ° C, the viscosity of the air becomes equal to 233.7 10 -6 m 2 / s, that is, it increases 15.5 times! The dynamic viscosity of air at a temperature of 20°C is 18.1·10 -6 Pa·s.
When air is heated, the values of both kinematic and dynamic viscosity increase. These two quantities are interconnected through the value of air density, the value of which decreases when this gas is heated. An increase in the kinematic and dynamic viscosity of air (as well as other gases) during heating is associated with a more intense vibration of air molecules around their equilibrium state (according to the MKT).
| t, °С | μ 10 6 , Pa s | ν 10 6, m 2 / s | t, °С | μ 10 6 , Pa s | ν 10 6, m 2 / s | t, °С | μ 10 6 , Pa s | ν 10 6, m 2 / s |
|---|---|---|---|---|---|---|---|---|
| -50 | 14,6 | 9,23 | 70 | 20,6 | 20,02 | 350 | 31,4 | 55,46 |
| -45 | 14,9 | 9,64 | 80 | 21,1 | 21,09 | 400 | 33 | 63,09 |
| -40 | 15,2 | 10,04 | 90 | 21,5 | 22,1 | 450 | 34,6 | 69,28 |
| -35 | 15,5 | 10,42 | 100 | 21,9 | 23,13 | 500 | 36,2 | 79,38 |
| -30 | 15,7 | 10,8 | 110 | 22,4 | 24,3 | 550 | 37,7 | 88,14 |
| -25 | 16 | 11,21 | 120 | 22,8 | 25,45 | 600 | 39,1 | 96,89 |
| -20 | 16,2 | 11,61 | 130 | 23,3 | 26,63 | 650 | 40,5 | 106,15 |
| -15 | 16,5 | 12,02 | 140 | 23,7 | 27,8 | 700 | 41,8 | 115,4 |
| -10 | 16,7 | 12,43 | 150 | 24,1 | 28,95 | 750 | 43,1 | 125,1 |
| -5 | 17 | 12,86 | 160 | 24,5 | 30,09 | 800 | 44,3 | 134,8 |
| 0 | 17,2 | 13,28 | 170 | 24,9 | 31,29 | 850 | 45,5 | 145 |
| 10 | 17,6 | 14,16 | 180 | 25,3 | 32,49 | 900 | 46,7 | 155,1 |
| 15 | 17,9 | 14,61 | 190 | 25,7 | 33,67 | 950 | 47,9 | 166,1 |
| 20 | 18,1 | 15,06 | 200 | 26 | 34,85 | 1000 | 49 | 177,1 |
| 30 | 18,6 | 16 | 225 | 26,7 | 37,73 | 1050 | 50,1 | 188,2 |
| 40 | 19,1 | 16,96 | 250 | 27,4 | 40,61 | 1100 | 51,2 | 199,3 |
| 50 | 19,6 | 17,95 | 300 | 29,7 | 48,33 | 1150 | 52,4 | 216,5 |
| 60 | 20,1 | 18,97 | 325 | 30,6 | 51,9 | 1200 | 53,5 | 233,7 |
Note: Be careful! The viscosity of air is given to the power of 10 6 .
Specific heat capacity of air at temperatures from -50 to 1200°С
A table of the specific heat capacity of air at various temperatures is presented. The heat capacity in the table is given at constant pressure (isobaric heat capacity of air) in the temperature range from minus 50 to 1200°C for dry air. What is the specific heat capacity of air? The value of specific heat capacity determines the amount of heat that must be supplied to one kilogram of air at constant pressure to increase its temperature by 1 degree. For example, at 20°C, to heat 1 kg of this gas by 1°C in an isobaric process, 1005 J of heat is required.
The specific heat capacity of air increases as its temperature rises. However, the dependence of the mass heat capacity of air on temperature is not linear. In the range from -50 to 120°C, its value practically does not change - under these conditions, the average heat capacity of air is 1010 J/(kg deg). According to the table, it can be seen that the temperature begins to have a significant effect from a value of 130°C. However, air temperature affects its specific heat capacity much weaker than its viscosity. So, when heated from 0 to 1200°C, the heat capacity of air increases only 1.2 times - from 1005 to 1210 J/(kg deg).
It should be noted that the heat capacity of moist air is higher than that of dry air. If we compare air, it is obvious that water has a higher value and the water content in the air leads to an increase in specific heat.
| t, °С | C p , J/(kg deg) | t, °С | C p , J/(kg deg) | t, °С | C p , J/(kg deg) | t, °С | C p , J/(kg deg) |
|---|---|---|---|---|---|---|---|
| -50 | 1013 | 20 | 1005 | 150 | 1015 | 600 | 1114 |
| -45 | 1013 | 30 | 1005 | 160 | 1017 | 650 | 1125 |
| -40 | 1013 | 40 | 1005 | 170 | 1020 | 700 | 1135 |
| -35 | 1013 | 50 | 1005 | 180 | 1022 | 750 | 1146 |
| -30 | 1013 | 60 | 1005 | 190 | 1024 | 800 | 1156 |
| -25 | 1011 | 70 | 1009 | 200 | 1026 | 850 | 1164 |
| -20 | 1009 | 80 | 1009 | 250 | 1037 | 900 | 1172 |
| -15 | 1009 | 90 | 1009 | 300 | 1047 | 950 | 1179 |
| -10 | 1009 | 100 | 1009 | 350 | 1058 | 1000 | 1185 |
| -5 | 1007 | 110 | 1009 | 400 | 1068 | 1050 | 1191 |
| 0 | 1005 | 120 | 1009 | 450 | 1081 | 1100 | 1197 |
| 10 | 1005 | 130 | 1011 | 500 | 1093 | 1150 | 1204 |
| 15 | 1005 | 140 | 1013 | 550 | 1104 | 1200 | 1210 |
Thermal conductivity, thermal diffusivity, Prandtl number of air
The table shows such physical properties of atmospheric air as thermal conductivity, thermal diffusivity and its Prandtl number depending on temperature. The thermophysical properties of air are given in the range from -50 to 1200°C for dry air. According to the table, it can be seen that the indicated properties of air depend significantly on temperature and the temperature dependence of the considered properties of this gas is different.