Measuring Gases
Objectives:
• 1. Explain what gas pressure means and
describe how it is measured.
Key Terms:
• atmospheric pressure, barometer,
manometer, STP
Gas Variables - Amount
• Amount of Gas (n) - a mole is a standard amount of a
substance
– n = mass / molar mass (molar mass = atomic mass in
grams)
• In order to do this you need to calculate the molar mass of the substance.
– If the amount of gas in a closed system is increased then
the pressure is also increased.
• Increases the amount of collisions per unit time
Gas Variables - Volume
– Volume of Gas (V) - values are recorded in liters
(1000cc or 1000ml)
• if the amount (n) of gas is constant the pressure will
increase if the volume of the container is decreased
– Increases the number of collisions per unit time as the
molecules must travel a shorter distance
Gas Variables – Temperature
• Temperature (T) – Represents the kinetic energy of a gas
– all measurements will have to be converted to Kelvin
before calculations. (K = C + 273)
– the pressure in a closed container increases as the gas is
heated
• Number of collisions per unit time increases as the KE of each
molecule increases
Gas Variables – Pressure
• Pressure (P)- Pressure in a container is created by collisions of molecules
on the walls of the container.
–
it is created by manipulating the other 3 variables.
• (n) … directly related
• (V) … inversely related
• (T) … directly related
Standard Temp and Press
• STP
– This is a standard from which the properties of
gases are determined.
• Its values are:
– 273K (0oC)
– 1 atm (101.3 kPa or 760mmHg).