Information - Units of Gas Pressure There are several units used to measure gas
ID: 480569 • Letter: I
Question
Information - Units of Gas Pressure
There are several units used to measure gas pressure, the most commonly used unit in the United States is pounds per square inch (psi). This is a measure of the force in pounds exerted by a gas on one square inch of the surface of its container. The SI unit for gas pressure is the pascal (Pa) which is defined as the force in newtons per square meter. In most chemistry textbooks and in medical use the unit torr is preferred. The unit torr is the height of a column of mercury in mm (1 torr = 1 mm Hg) that can be supported by the applied pressure. Standard atmospheric pressure is given in several units in Table 1.
Table 1. Standard Pressure at Sea Level in Various Units
1 atm
760 mm Hg
760 torr
1013.25 mbar
1.01325 x 105 Pa
14.696 psi
29.92 in Hg
Model - Conversion of Between Pressure Units
Since so many different units of gas pressure are used, it is necessary to be able to make the simple conversions from one unit to another. The examples below show the process of converting from one unit to another.
What is the pressure in mm Hg if the reported atmospheric pressure is measured to be 29.45 in Hg?
What is the pressure in atm if the reported atmospheric pressure is measured to be 769 mm Hg?
Information - Significant Figures in These Calculations
In the calculations above, there are correctly four significant figures in the answers because the only measured value is the pressure reported to four significant figures, the conversion factors are based on exact definitions. A number in an exact definition is not considered in determining the significant figures in the answer.
What is the atmospheric pressure in torr if the measured atmospheric pressure is reported as 307.8 mm Hg?
1 atm
760 mm Hg
760 torr
1013.25 mbar
1.01325 x 105 Pa
14.696 psi
29.92 in Hg
Explanation / Answer
a) 29.92 in Hg pressure = 760 mmHg
29.45 in Hg pressure = 760×29.45/29.92 = 748.06 mmHg
ans- 748.06 mmHg
b) 760 mmHg pressure = 1atm
769mm Hg Pressure = 769/760 = 1.011atm
Ans- 1.011atm
2) 760 mmHg pressure = 760 torr
307.8 mmHg pressure = 307.8 torr
Ans- 307.8 torr