Gases: Pressure, Manometers, and Barometers

Focus: Interrelationship of pressure, volume, and temperature.
Application: Stoichiometry for gas-phase reactions.
Theory: Kinetic-molecular theory links microscopic gas behavior to macroscopic properties.

Definition: Force per unit area, P = F/A.
Principle: Smaller area for a given force results in higher pressure.
SI Unit: Pascal (Pa).
- 1 \text{ Pa} = 1 \text{ N/m}^2.
- Pascal is a very small unit (1 \text{ Pa} \approx 1/100,000 of sea-level atmospheric pressure).
Common Non-SI Units: Atmospheres (atm), kilopascals (kPa), bar, millimeters of mercury (mm Hg), torr, and pounds per square inch (psi).
**Conversion Factors (approximate values for quick recall):
- 1 \text{ atm} = 101,325 \text{ Pa} (101.325 kPa)
- 1 \text{ atm} = 1.01325 \text{ bar}
- 1 \text{ atm} = 760 \text{ mm Hg}
- 1 \text{ atm} = 760 \text{ torr}
- 1 \text{ atm} = 14.7 \text{ psi}
- 1 \text{ torr} = 1 \text{ mm Hg}

Purpose: Measures the pressure of a gas in a closed container.
Construction: U-tube (open to atmosphere) partially filled with mercury, connected to a gas container.
Mechanism: Mercury level difference (\Delta h) indicates the pressure difference between the gas and the atmosphere.
Observation: The side with higher pressure pushes the mercury level lower.

Purpose: Measures atmospheric pressure.
Construction: Long glass tube, closed at one end, filled with mercury, inverted into a mercury reservoir.
Mechanism: Atmospheric pressure on the reservoir supports the mercury column in the tube; countered by gravity.
Standard: At sea level, atmospheric pressure supports a mercury column of approximately 760 \text{ mm}$$.
Variation: Mercury height rises with increasing atmospheric pressure and falls with decreasing atmospheric pressure, reflecting weather changes.