Without 1 standard atmospheric pressure, must the temperature of boiling water be 100C?

No, in plateau areas, 80℃ will boil; If the air pressure is lower, it is estimated that the boiling temperature of water will be lower.

The boiling point of water changes with the change of atmospheric pressure: with the increase of atmospheric pressure, the boiling point also increases. This is because the atmospheric pressure on the water surface always prevents water molecules from evaporating, so when the air pressure rises, water must have a higher temperature to become steam.

On the contrary, if the air pressure decreases, the occupancy rate will also decrease. Because water molecules can't be prevented from escaping when the air pressure is low, water is easy to boil, although the temperature is not high at that time, which is why uncooked rice is cooked at high altitude by ordinary methods.

When the air pressure is lower than the standard atmospheric pressure, the boiling point of water will decrease. The reason why water boils is that after water molecules are heated, their irregular movements are enhanced, and finally they get rid of the constraints of the forces between water molecules and boil. When the atmospheric pressure decreases, water molecules are more likely to get rid of intermolecular forces and boil after being heated.

Extended data

A standard atmospheric pressure is specified as follows: the atmospheric pressure at sea level with a temperature of 0℃ and a latitude of 45 degrees is called 1 atmospheric pressure, and the value on the mercury barometer is 760 mm Hg (equivalent to10/3.25 hectopascals).

The change of atmospheric pressure is related to altitude. Atmospheric pressure is produced by gravity in the atmosphere. The higher the ground, the thinner the atmosphere, and the smaller the atmospheric pressure should be. However, because the air density related to the gravity received by the atmosphere varies unevenly with height, the atmospheric pressure decreases unevenly with height.

Change with height: atmospheric pressure decreases with the increase of height.

The change of atmospheric pressure is also related to the weather. At different times, the atmospheric pressure in the same place is not exactly the same. We know that the density of water vapor is less than that of air. When there is more water vapor in the air, the air density will become smaller and the atmospheric pressure will also decrease.

References:

Baidu encyclopedia-standard air pressure