Chapter 11 Gases

Gases: What Are They Like? Composed of widely separated particles in constant, random motion Flow readily and occupy the entire volume of their container Vapor is the term used to denote the gaseous state of a substance existing more commonly as a liquid e.g., water is a vapor, oxygen is a gas EOS Many low molar mass molecular compounds are gases – methane (CH4), carbon monoxide (CO) Chapter 5: Gases

Kinetic-Molecular Theory Provides a model for gases at the microscopic level Molecules move in straight lines until they contact something else Temperature is the average kinetic energy of the Particles EOS Chapter 5: Gases

Kinetic Moleccular Theory A gas consists of a collection of small particles traveling in straight-line motion and obeying Newton's Laws. The molecules in a gas occupy no volume (that is, they are points). Collisions between molecules are perfectly elastic (that is, no energy is gained or lost during the collision). There are no attractive or repulsive forces between the molecules. The average kinetic energy of a molecule in all gases is the same

Molecular Diffusion Diffusion is the process by which one substance mixes with one or more other substances as a result of the translational motion of molecules EOS Chapter 5: Gases

Effusion Effusion is the process in which a gas escapes from its container through a tiny hole, or orifice EOS Chapter 5: Gases

Gas Pressure Pressure is the force per unit area – consider the unit pounds per square inch SI units express pressure in Newtons (N) per square meters (m2) -- or N m–2 a.k.a. – Pascals (Pa) EOS A barometer is an instrument used to measure atmospheric pressure Chapter 5: Gases

Barometers Used to measure atmospheric pressure The pressure exerted by a column of mercury exactly 760 mm high is defined as 1 atmosphere (atm) EOS Gases tend to settle under the effects of gravity – pressure  as altitude  Chapter 5: Gases

Examples of Pressure Units Given these values, one can generate conversion factors to switch between units: e.g., 760 mmHg = 1.01325 bar EOS Chapter 5: Gases

Molar Volumes and Standard Pressure and Temperature Standard Temperature and Pressure (STP) is defined as T = 0 oC and P = 101.3kPa EOS The molar volume of a gas is the volume occupied by one mole of the gas at STP= 22.4 L/mol Chapter 5: Gases

Molar Volumes and Standard Ambient Pressure and Temperature Standard AmbientTemperature and Pressure (SATP) is defined as T = 25 oC and P = 100kPa 24.8 EOS The molar volume of a gas is the volume occupied by one mole of the gas at SATP= 24.8 L/mol Chapter 5: Gases

Temperature-Volume Relationship: Charles’s Law The volume of a fixed amount of a gas at constant pressure is directly proportional to its Kelvin temperature i.e., if V , then T  or V/T = k EOS Chapter 5: Gases

Temperature-Volume Relationship: Charles’s Law Absolute zero is the temperature obtained by extrapolation to zero volume EOS Absolute zero on the Kelvin scale = –273.15 °C and ... 273.15 K = 0 °C Chapter 5: Gases

Pressure-Volume Relationship: Boyle’s Law For a given amount of a gas at constant temperature, the volume of the gas varies inversely with its pressure i.e., if V , then P  EOS Chapter 5: Gases

Pressure-Volume Relationship Boyle’s Law EOS or V = k*1/P P1V1=P 2V2 For a given amount of a gas at constant temperature, the product of the pressure and the volume is a constant PV = k Chapter 5: Gases

Pressure- temperatureRelationship Gay-Lussac’s Law EOS / For a given amount of a gas at constant volume, the pressure of a gas is proportional to its temperature Chapter 5: Gases

For initial and final conditions: The Combined Gas Law Given the various gas laws, all can be combined into a single form … V = k/P, V = kT, and V = kn V a (nT)/P For initial and final conditions: EOS Chapter 5: Gases