Chemistry 1050 – Section 5.2: Pressure

What is pressure?
The result of the constant collisions between the atoms or molecules in a gas and the surfaces around them.
What are high pressure weather systems usually associated with?
Clear weather.
What are low pressure weather systems usually associated with?
Unstable weather.
What is the relationship between the number of gas particles and the pressure?
The fewer the gas particles, the lower the pressure.
What is a barometer?
A barometer is an evacuated glass tube, the tip of which is submerged in a pool of mercury.
When the atmospheric pressure rises, what happens to the height of the mercury column in a barometer?
The height of the mercury column rises.
When the atmospheric pressure falls, what happens to the height of the mercury column in a barometer?
The height of the column falls.
What is a millimetre of mercury often called?
A torr.
What is standard pressure?
Exactly 100, 000Pa or 1bar.
What is a manometer?
A manometer is a U-shaped tube containing a dense liquid, usually mercury.
If the atmospheric pressure is equal to the gas pressure, what happens to the mercury levels in a manometer?
The mercury levels on both sides of the tube are the same.
If the gas pressure is greater than the atmospheric pressure, what happens to the mercury levels in a manometer?
The mercury level on the open-side of the tube is higher than the gas-side.
If the gas pressure is less than the atmospheric pressure, what happens to the mercury levels in a manometer?
The mercury level on the gas-side will be higher than the open-side.
In a manometer, what does the difference in height of the mercury levels represent?
The difference in height is equal to the difference between the gas’s pressure and the atmospheric pressure.