Gas Laws

# Gas Laws - CHAPTER 5 PROPERTIES OF GASES Physical...

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1 CHAPTER 5 PROPERTIES OF GASES Physical properties of gases: Expand to fill their container Are very compressible Have low density (i.e., mass per unit volume) Mix completely to form a homogenous mixture (solution) Important parameters of gases : Pressure ( P ), Volume ( V ), Temperature ( T ), and Amount (moles, n ) Substances with different physical properties as solids or liquids have very similar physical properties as gases . All gases exert pressure . What is Pressure ? A force pushing against surface. A F = = area force Pressure SI Units of Pressure First consider Force : F = ma m = mass (kg) a = acceleration (m/s 2 ) Force = kg m/s 2 Î newton (N Force = kg·m/s newton (N) SI unit of force is the newton (N) Pressure : 2 2 2 2 N/m s kg/m m m/s kg = = = = A F P PRESSURE UNITS SI unit of pressure is the pascal (Pa). The atmosphere exerts a pressure . 2 2 N/m 1 s kg/m 1 Pa 1 = = This pressure is a consequence of the gravitational pull of earth. Consider the weight of a column of air (1 square inch column ) extending up to the upper limit of the atmosphere (about 100 miles). F = m·a Weight ( W ) = m·g A column of air 1 inch square has a weight of 14.7 pounds (lbs). lbs/in 14.7 in 1 lbs 14.7 2 2 = = = A F P Hence: Figure 5.2

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2 If the area is increased, then the force exerted increases as well because the ratio is constant : What is the force exerted by a 1 square foot (constant) lbs/in 14.7 in 1 lbs 14.7 2 2 = = = A F P () lbs 2,120 ft 1 ft 1 in 12 lbs/in 14.7 2 2 2 = = = A P F column of air? Atmospheric pressure is a powerful force!!!!! 1 m 2 column of air has a weight of 10,000 kg (about 22,000 lbs or 11 tons) Effect of Pressure on a Container The pressure of the atmosphere can be measured by using a device called a barometer . Barometer : A tube, closed at one end , filled with liquid mercury (Hg ; inverted in a pool of with liquid mercury (Hg) ; inverted in a pool of mercury. The Hg level drops some ; it does not run completely out, it simply drops to a particular level. TYPICAL BAROMETER P = balance atm Hg balance between the two Figure 5.3 PRESSURE Normal atmospheric pressure supports a column of Hg 760 mm high (0 °C at sea level). 1 atm pressure = 760 mm Hg; exactly by definition 1 atm = 101 325 Pa (exactly 1 atm = 101,325 Pa (exactly) 101,325 Pa = 760 mm Hg Another common unit of pressure: torr 1 torr = 1 mm Hg (exactly) (exactly) 760 atm 1 Hg mm 1 torr 1 = =
3 Consider a water barometer The density ( d ) of the liquid in the barometer is important. Consider two liquids, mercury and water : Hg: = 13.6 g/mL H O: = 1 0 g/mL H 2 O: = 1.0 g/mL Since water is less dense than mercury, 1 atm pressure will support a higher column of water. How much higher?? nsity) height)(de (column P Column Heights Solving for h B gives: B B A A d h d h P = B A A B d d h h = g/mL mm)(13 6 (760 Hence, a water barometer would be over 10 m high or in the English system : mm 10,336 g/mL 1.0 g/mL) mm)(13.6 water = = h () ft 33.91 in. 12 ft 1 mm 25.4 in. 1 mm 10,336 = 1) Water barometer is 3 stories tall !!

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Gas Laws - CHAPTER 5 PROPERTIES OF GASES Physical...

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