Notes

Outline

Gases

Characteristics of Gases Color Chlorine-greenish yellow Hydrogen, Oxygen,Nitrogen-Colorless Nitrogen Oxides-reddish brown Iodine-purple Odor Chlorine, Bromine-irritating stinging HCl-biting odor Oxygen, Hydrogen, Nitrogen-odorless Toxicity Oxygen, Nitrogen, Hydrogen-non-toxic Carbon Monoxide, Carbon Dioxide-Toxic

Four Variables of Gases Pressure Temperature Volume Amount of Gas

Pressure and Pressure Units Pressure-Force per unit area = F / A Pressure units mmHg cmHg Atmospheres Pascals KiloPascals 760 mm Hg = 76 cm Hg = 1 atm = 103.1kPa

Pressure Instruments Manometer Closed ended Pgas = h2-h1 Open ended Pgas = Pbar + (h2-h1) Barometer

T-92  Manometers(Open and Closed)

T-91 Barometer

Ideal Gas Laws Boyles Law (Volume-Pressure) Charles Law (Volume-Temperature) Avagadro’s Law (Volume-mole) Gay-Lusaac’s Law (Pressure-Temperature) Combined Gas Law Ideal Gas Law

Boyle’s Law Inverse Relationship between Volume and Pressure V~1 / P V =k / P V1 P1 = V2 P2 Graphical Representation Boyles Law Problems

Kelvin Scale Developed by Lord Kelvin K = C + 273.15 Used in all equations where Temperature is one of the variables Temperature Conversion Problems

Charles Law Volume-Temperature Relationship V~  T V = kT V1 / T1 = V2 / T2 Graphical Representation Charles Law Problems

Avagadro’s Law Volume-mole relationship V~n V = kn V1 / n1 = V2 / n2 Graphical Representation Avagadro Law Problems

Ideal Gas Law Volume-Pressure-Temperature-mole Relationship PV = nRT R = .0821 Liter-Atm / mol-K P= Pressure in atm V = Volume in Liters T = Temperature in Kelvin N = mols of gas V = k / P    V = kT   V = kn      PV=knT Use in single set of variables Ideal Gas Law Problems

Derivations of Boyles Law, Charles Law, and Avagadro’s Law using Ideal Gas Law R = PV / nT P1V1 / n1T1 = P2V2 / n2T2 Boyles Law n1 = n2 and T1 = T2 P1V1 = P2V2 Charles Law n1 = n2   and P1 = P2 V1 / T1 = V2 / T2 Avagadro’s Law P1 = P2   and  T1 = T2 V1 / n1 = V2 / n2

Gay Lusaac Law Pressure- Temperature Relationship n1 = n2  and  V1 = V2 P1 / T1 = P2 / T2 Gay Lusac Law Problem

Combined Gas Law Volume-Temperature-Pressure Relationship n1 = n2 P1 V1 / T1 = P2 V2 / T2 Combined Gas Law Problem

Density of Gases PV = nRT N = wt of gas / MM PV = (wt of gas / MM )RT Wt of gas / V = D = P(MM) / RT Density Problem

Molar Mass (Molecular Weight) of Gases D = P MM / R T MM = D R T / P Molar Mass Problem

Gaseous Stoichiometry Mol-volume or volume-mol Mols given--à mols of requested--à volume requested Mass-volume or volume-mass Mass given--à mols given---àmols requested--àvolume requested Volume-Volume Use law of combining volumes Example

Dalton’s Law of Partial Pressures Partial Pressure-Pressure of a gas in a mixture as if occupied the container alone Assumes that in a mixture large distances between molecules reduce influence of other gases to zero Ptotal = P1  +  P2  +  P3 …..+ Pn

Determining Partial Pressures Using Ideal Gas Law P1V1 = n1RT1 P1 = n1RT1 / V1 Problem

Mole Fraction and Partial Pressure Mole Fraction-mols of one component / Total mols of all components in the mixture P1 = X1Ptotal Problem

Collecting a Gas Over Water-Application of Dalton’s Law P1 = Pbar – PH2O Problem

Kinetic Molecular Theory 1.All gases are composed of molecules in random motion 2. The volume of the actual gas molecules are considered negligible (approaching zero) 3. Attractive and repulsive forces between gas molecules are considered negligible (approaching zero) 4. The average Kinetic Energy of all molecules in a gas sample varies with temperature 5. All collisions between molecules are considered perfectly elastic (complete conservation of momentum)

Boyles Law Predicted By KMT Volume increase will increase the surface area for collisions thereby reducing the number of collisions per sq cm(Pressure)

Charles Law Predicted by KMT Increasing the temperature will increase the average  thereby causing the molecules to travel faster and the number of collisions per sq cm to increase

Graham’s Law of Diffusion (Effusion) R~(MM)1/2 R1 / R2 = (MM)2 1/2 / (MM)1 ½ t2 / t1 = (MM)2 ½ / (MM)1 ½ Problem

Factors Causing Ideal Gas Deviation Molecular Volume Intermolecular Forces

Temperature and Pressure Effects On Ideal Gas Behavior Low temperature causes greater deviation from Ideal Gas Behavior Lower temperature decreases average Kinetic Energy thereby increasing Intermolecular forces effect on molecules Higher Pressure causes greater deviation Decreases distance between molecules thereby increasing Intermolecular Forces

T-95  Deviation of Gases With Pressure

T-96   Deviation From Ideality With Temperature

Van Der Waals(Real Gas) Equation Compensates for actual deviation [P + a(n / V) 2] (V- bn) = nRT a and b = Van Der Waals Constants “a”  compensates for intermolecular forces “b” compensates for molecular volume n = number of mols