# Ch02-gas - 4.1 An Overview of the Physical States of Matter...

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4-1 Distinguishing gases from liquids and solids.An Overview of the Physical States of Matter Gas volume changes significantly with pressure. Solid and liquid volumes are not greatly affected by pressure. Gas volume changes significantly with temperature. Gases expand when heated and shrink when cooled. The volume change is 50 to 100 times greater for gases than for liquids and solids. Gases flow very freely. Gases have relatively low densities. Gases form a solution in any proportions. Gases are freely miscible with each other. 4.1
4-2 Figure 4.1 The three states of matter.
4-3 Gas Pressure and its Measurement Pressure = force area Atmospheric pressure arises from the force exerted by atmospheric gases on the earths surface. Atmospheric pressure decreases with altitude. 4.2
4-4 Figure 4.2 Effect of atmospheric pressure on a familiar object.
4-5 Figure 4.3 A mercury barometer.
4-6 Figure 4.4 The Hg levels are equal because both arms of the U tube are evacuated. Closed-end manometer A gas in the flask pushes the Hg level down in the left arm. The difference in levels, Δh, equals the gas pressure, Pgas.Two types of Manometers
4-7 Figure 4.4 Open-end manometer When Pgasis less than Patm, subtract Δhfrom Patm. Pgas< Patm Pgas= Patm- ΔhWhen Pgasis greater than Patm, add Δhto Patm. Pgas> Patm Pgas= Patm+ Δh
4-8 Table 4.1Common Units of Pressure
4-9 Sample Problem 4.1 Converting Units of Pressure PROBLEM: A geochemist heats a limestone (CaCO3) sample and collects the CO2released in an evacuated flask attached to a closed-end manometer. After the system comes to room temperature, Δh= 291.4 mm Hg. Calculate the COpressure in units of bars and kilopascals. PLAN: Construct conversion factors to find the other units of pressure.2
4-10 The Gas LawsThe gas laws describe the physical behavior of gases in terms of 4 variables: pressure (P)temperature (T) volume (V) amount (number of moles, n) An ideal gasis a gas that exhibits linear relationships among these variables. No ideal gas actually exists, but most simple gases behave nearly ideally at ordinary temperatures and pressures.4.3
4-11 Figure 4.5 Boyles law, the relationship between the volume and pressure of a gas.
4-12 Boyles Law At constant temperature, the volume occupied by a fixed amount of gas is inverselyproportional to the external pressure. V 1 P or PV= constant At fixed Tand n, Pdecreases as Vincreases Pincreases as Vdecreases
4-13 Figure 4.6(A,B) Charless law, the relationship between the volume and temperature of a gas.
4-14 Figure 4.6 C Charless law, the relationship between the volume and temperature of a gas.
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