Atmosphere (unit) for the purposes of specifying the physical properties of substances, “"standard pressure"” should be precisely . A pressure of 1 atm can also be stated as: Scuba divers and others use the word "atmosphere" and "atm" in relation to pressures that are relative to mean atmospheric pressure at sea level (1.013 bar). For example, a partial pressure of oxygen is calibrated typically using air at sea level, so is expressed in units of atm. The old European unit technical atmosphere (at) is equal to 1 kilogram-force per square centimetre (kgf/cm), Pa. Atmosphere (unit) The standard atmosphere (symbol: atm) is a
Standard state concentration, to a specified condition (usually unit concentration or pressure) using an ideal extrapolating function, such as ideal solution or ideal gas behavior, or by empirical measurements. The standard state for a gas is the hypothetical state it would have as a pure substance obeying the ideal gas equation at standard pressure (10 Pa, or 1 bar). No real gas has perfectly ideal behavior, but this definition of the standard state allows corrections for non-ideality to be made consistently for all the different gases. The standard state for liquids and solids is simply the state of the pure substance subjected