Pressure and Temperature
Gases can be measured in terms of:
Measurement
Amount Volume Pressure Temperature |
Standard Unit
mole liter atmosphere Kelvin |
We have already discussed amount, measured in moles, and volume. So, here we will focus on pressure and temperature.
Pressure is the result of the gas particles colliding with the walls of the container it is in. Every time a particle hits the wall of the container, it exerts a force or push. Pressure is a measure of this force over the whole container. When the particles hit either with more force or more often (both due to faster molecule movement), the pressure will increase. Atmospheric pressure is the weight of the air above an object. When you are standing at sea level, there is a lot of air above you. All that air is essentially sitting on your shoulders, holding you down. That weight of gas at sea level is 14.7 pounds of pressure on every square inch of your body. You do not feel this weight because your body is used to it. It has been there every day of your life. Since 14.7 psi is a hard number to work with, scientists have developed an alternative unit as the standard. The atmosphere (atm) is equal to 14.7 psi. The unit was developed simply: At sea level, a person has exactly one Earth's atmosphere of air above them. Therefore, the air pressure at sea level is 1 atmosphere. As a person travels up from sea level, the amount of air above that person is less, or that person has less than one atmosphere above them. What would that atmospheric pressure be in Death Valley, which is 100 ft below sea level? Units of Pressure |
There are several other common units of pressure (just like there are several ways to measure distances). These units were all developed in different ways, but all of these are equal to one another at sea level
1 atmosphere = 760 mm Hg = 760 torr = 101,325 Pa = 101.325 kPa = 14.7 psi
Example of a pressure conversion: Suppose the pressure on a balloon in mid-air is 320 torr. What is the pressure in psi?
Temperature
Temperature is the measure of the movement of the molecules in a substance. As heat energy is added to a material, the molecules of the material move faster (radiant heat energy transformed into kinetic energy of the molecules). Temperature is a measure of how fast the molecules are moving. Just like pressure, there is more than one temperature scales in use. In science, either the Celsius (OC) or the Kelvin (K) temperature scale is used. The conversions for these scales and the Fahrenheit (OF) scale are below:
oC = 5/9(oF - 32)
oF = 9/5(oC) + 32
K = oC + 273
oC = K - 273
oF = 9/5(oC) + 32
K = oC + 273
oC = K - 273
Absolute Temperature
An absolute scale means that it has limits on one or both ends of the scale. The Kelvin temperature scale cannot go below 0 K because this temperature corresponds to the point where the motion of the particles (their kinetic energy) ceases. If there is no movement of the particles, there is no temperature. This point is called absolute zero. In other words, it is physically impossible to go below the following temperatures:
An absolute scale means that it has limits on one or both ends of the scale. The Kelvin temperature scale cannot go below 0 K because this temperature corresponds to the point where the motion of the particles (their kinetic energy) ceases. If there is no movement of the particles, there is no temperature. This point is called absolute zero. In other words, it is physically impossible to go below the following temperatures:
0 K = -273 oC = -459.4 oF