What is the normal atmospheric pressure?
101.325kPa.
Standard atmospheric pressure is the air pressure at sea level under standard atmospheric conditions. It was proposed by the physicist Torricelli in 1644. Its value is 101.325kPa. It is the unit of pressure and is recorded as atm. .
In chemistry, standard temperature and pressure (STP) was once defined as 0°C (273.15K) and 101.325kPa (1atm), but since 1982, IUPAC redefined "standard pressure" as 100 kPa . 1 standard atmospheric pressure = 760mm mercury = 76cm mercury = 1.01325×10^5Pa = 10.339m water column.
Extended information:
The regulations of standard atmospheric pressure values have undergone several changes with the development of science and technology. It was originally specified that the atmospheric pressure at sea level at a temperature of 0°C, a latitude of 45°, and a clear day is the standard atmospheric pressure, which is approximately equivalent to a height of 760 mm of mercury. Later, it was discovered that the atmospheric pressure value under this condition is not stable and changes due to the influence of wind, temperature and other conditions.
So the height of 760mm of mercury was specified as the standard atmospheric pressure value. But later it was discovered that the pressure value as high as 760 mm of mercury was also unstable. The density of mercury changed due to the influence of temperature; the g value also changed with latitude. In order to ensure that the standard atmospheric pressure is a fixed value, the resolution of the 10th International Conference on Weights and Measures in 1954 stated that the standard atmospheric pressure value is 101.325kPa.
The Earth is surrounded by thick air, which is called the atmosphere. Air can flow as freely as water, but it is also affected by gravity. Therefore, there is pressure inside the air in all directions. This pressure is called atmospheric pressure. In 1643, Italian scientist Torricelli filled an 80cm-long thin glass tube with mercury and placed it upside down in a water tank containing mercury. He found that the mercury in the glass tube dropped by about 4cm and then stopped falling.
No air enters this 4cm space, it is a vacuum. Torricelli concluded from this that the pressure of the atmosphere is equal to the length of the mercury column. According to the pressure formula, scientists have accurately calculated that the atmospheric pressure under standard conditions is 1.01×10^5 Pa (Pa). In order to confirm the existence of atmospheric pressure and vacuum, Glick conducted the famous Magdeburg Hemisphere Experiment in Magdeburg, Germany in 1654, which gave people a profound understanding of atmospheric pressure.
Baidu Encyclopedia-Standard Atmospheric Pressure