Pressure Concepts and Gas Laws

Pressure Concepts

• Pressure is defined as the force exerted per unit area, predominantly from gas molecules striking surfaces.
• Atmospheric pressure at sea level is commonly measured in atmospheres (atm) and millimeters of mercury (mmHg).
• A barometer is utilized to measure atmospheric pressure, while a manometer assesses the pressure of gas samples.

Pressure Units

• Millimeter of Mercury (mmHg) indicates air pressure sufficient to elevate mercury by 1 mm in a barometer.
• Pascal (Pa) is the International System (SI) unit for measuring pressure.
• 1 atm of pressure is the average air pressure at sea level and is equal to 101.325 kPa.

Gas Laws

• Boyle's Law states that gas volume is inversely related to pressure (P inversely proportional to V).
• Charles's Law establishes a direct relationship between gas volume and temperature (V directly proportional to T).
• Avogadro's Law asserts that volume is directly proportional to the number of moles of gas (V directly proportional to n).

Ideal Gas Behavior

• The ideal gas law combines Boyle's, Charles's, and Avogadro's laws, represented as PV = nRT, where R is the ideal gas constant (0.0821 L·atm/K·mol).
• An ideal gas perfectly follows the ideal gas law under all conditions.

Molar Volume and Standard Conditions

• Molar volume refers to the space occupied by one mole of a substance, often used under standard conditions.
• Standard Temperature and Pressure (STP) is defined at 0° C (273 K) and 1 atm.

Gas Mixtures and Partial Pressures

• The partial pressure (Pⁿ) is the pressure exerted by an individual gas in a mixture.
• Dalton's law of partial pressures states that the total pressure in a gas mixture equals the sum of the partial pressures of its constituents.
• The mole fraction (Xa) represents the ratio of moles of a component to the total moles in a mixture.

Physiological Effects of Pressure Changes

• Hypoxia arises from low oxygen levels, leading to dizziness and in severe cases, unconsciousness.
• Oxygen toxicity results from high blood oxygen levels, causing muscle twitching and convulsions.
• Nitrogen narcosis occurs with increased nitrogen partial pressure, producing effects similar to alcohol intoxication.

Vapor and Kinetic Theory

• Vapor pressure is the partial pressure of a vapor in equilibrium with its liquid phase.
• Kinetic molecular theory models gases as particles in constant motion that collide elastically.
• Mean free path quantifies the average distance traveled by a gas molecule between collisions.

Gas Movement

• Diffusion describes the gas spreading process within another gas's space.
• Effusion refers to gas escaping from a container through a small opening into a vacuum.

Nonideal Gas Behavior

• The van der Waals equation modifies the ideal gas law to incorporate intermolecular forces and the volume occupied by gas particles.