http://www.ck12.org Chapter 13. States of Matter
FIGURE 13.3
(A) A barometer measures atmospheric
pressure as the height of a column of
mercury. (B) A more modern aneroid
barometer can be read by looking at the
position of a dial. Barometers are fre-
quently used by meteorologists to help
them predict upcoming weather patterns.FIGURE 13.4
A manometer is used to measure the pressure of an enclosed gas sample.
The difference in height (∆h) between the two arms of the U-tube indicates
the gas pressure.Units of Gas Pressure
As seen above, a barometer measures gas pressure by the height of the column of mercury. One unit of gas pressure
is the millimeter of mercury (mmHg). An equivalent unit to the mmHg is called the torr, in honor of the inventor
of the barometer, Evangelista Torricelli. Thepascal (Pa)is the standard unit of pressure. A pascal is a very small
amount of pressure, so a more useful unit for everyday gas pressures is the kilopascal (kPa). A kilopascal is equal
to 1000 pascals. Another commonly used unit of pressure is the atmosphere (atm). Standard atmospheric pressure
is called 1 atm of pressure and is equal to 760 mmHg and 101.3 kPa.
1 atm = 760 mmHg = 760 torr = 101.3 kPaIt is important to be able to convert between different units of pressure. To do so, we will use the equivalent standard
pressures shown above.
Sample Problem 13.1: Pressure Unit Conversions
The atmospheric pressure in a mountainous location is measured to be 613 mmHg. What is this pressure in atm and
in kPa?
Step 1: List the known quantities and plan the problem.