Gases An Exploration in Ideal Gas Behavior Loosely adapted from: Philip Dutton University of Windsor, Canada and Martin Silberberg

Some Important Industrial Gases Name (Formula) Origin and use Methane (CH 4 ) Natural deposits; domestic fuel Ammonia (NH 3 ) From N 2 + H 2 ; fertilizers, explosives Chlorine (Cl 2 ) Electrolysis of seawater; bleaching and disinfecting Oxygen (O 2 ) Liquified air; steelmaking Ethylene (C 2 H 4 ) High-temperature decomposition of natural gas; plastics

Helium He 4.0 NeonNe 20.2 ArgonAr 39.9 HydrogenH NitrogenN Nitrogen monoxide NO 30.0 OxygenO Hydrogen chloride HCl 36.5 OzoneO AmmoniaNH MethaneCH Substances That Are Gases under Normal Conditions Substance Formula MM(g/mol)

The Three States of Matter

Important Characteristics of Gases 1) Gases are highly compressible An external force compresses the gas sample and decreases its volume; removing the external force allows the gas volume to increase. 2) Gases are thermally expandable When a gas sample is heated, its volume increases; when it is cooled its volume decreases. 3) Gases have low viscosity Gases flow more easily than liquids or solids.

Important Characteristics of Gases 4) Most Gases have low densities Gas densities are on the order of grams per liter whereas liquids and solids are grams per cubic cm, 1000 times greater. 5) Gases are infinitely miscible Gases mix in any proportion. An example of such is air, a mixture of many gases.

Properties of Gases: Gas Pressure Gas Pressure Liquid Pressure P (Pa) = Area (m 2 ) Force (N) P = g ·h ·d

Pressure of the Atmosphere Called “atmospheric pressure,” or the force exerted upon us by the atmosphere above us. A measure of the weight of the atmosphere pressing down upon us. Measured using a barometer - A device that can “weigh” the atmosphere above us. Pressure = Force Area

A Mercury Barometer

Effect of Atmospheric Pressure on Objects at the Earth’s Surface

Construct a Barometer Using Water d water = 1.00 g/cm 3 d Hg = 13.6 g/cm 3 Height of water column = H w …of Hg column = H Hg H W = 10.3 m = 33.8 ft

The Mystery of the Suction Pump Because of the density of water, a “suction” pump can only pull water from a maximum depth of ~10 m (~34 feet) regardless of the quality of the vacuum or how fast the handle is pumped. For wells deeper than 34 feet, the water must be pushed up from below.

Manometers

Common Units of Pressure Unit Atmospheric Pressure Scientific Field pascal (Pa); x 10 5 Pa SI unit; physics, kilopascal(kPa) kPa chemistry atmosphere (atm) 1 atm* Chemistry millimeters of mercury 760 mmHg* Chemistry, medicine, ( mm Hg ) biology torr 760 torr* Chemistry pounds per square inch 14.7 lb/in 2 Engineering ( psi or lb/in 2 ) bar bar Meteorology, biology chemistry, physics

Converting Units of Pressure Problem: A chemist collects a sample of carbon dioxide from the decomposition of limestone (CaCO 3 ) in a closed end manometer, the height of the mercury is mm Hg. Calculate the CO 2 pressure in torr, atmospheres, and kilopascals. Solution: P CO2 (torr) = mm Hg x = torr 1 torr 1 mm Hg converting from mmHg to torr: converting from torr to atm: P CO2 ( atm) = torr x = atm 1 atm 760 torr converting from atm to kPa: P CO2 (kPa) = atm x = kPa kPa 1 atm

Characterization of a Gas Sample To fully characterize any gas sample, 4 variables must be accounted for: Pressure (P) Volume (V) Quantity of gas in moles (n) Kelvin Temperature (T)

Experiment this week Determine the relationship between: P and V P and T

Vernier Pressure Sensor Note: Pressure must not exceed 220 kPa. Start with syringe at 10 mL and compress no further than 5 mL. Draw plunger back to get larger volumes. Set up LoggerPro to collect data on command: Experiment | Data Collection Change Mode: Events with Entry A Note on Pressure Versus Temperature: What must be constant? Use a small Erlenmeyer flask and the plastic tubing to attach the sensor. Clamp the flask below the surface of water in a big beaker. Use ice for subambient temperatures. Heat to no hotter than about 80°C Lots of little parts. Please don’t lose them. Use a 60 mL syringe rather than the 20 mL supplied in the box. Attach syringe to Leur-lock with a gentle push… …then a gentle twist. It doesn’t have to be really tight. Really, it doesn’t.

Other Notes The thermometers don’t know how to swim! –Please don’t teach them This investigation, Author 2: Introduction and Conclusion 3: Discussion 1: Data/Results and Experimental This investigation, Author B: Introduction, Conclusion, Data/Results A: Discussion and Experimental