Exp10_Prelab - Experiment 10 Experimen.ng with Gas Laws...

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Unformatted text preview: Experiment 10: Experimen.ng with Gas Laws Learning Objec.ves: •  Ideal Gas Law •  PV = nRT •  Examine 2 Rela2onships within Gas Laws –  Boyle’s Law: Pressure and Volume –  Gay‐Lussac’s Law: Pressure and Temperature •  Experimentally Gas Constant (R) using both Laws •  Determine Absolute Zero using Gay‐Lussac’s Law Gases •  Gas molecule movement is rapid, random, and chao.c •  Gases occupy volume (think of a balloon) •  IDEAL GASES –  Molecules in an ideal gas do not exert forces on one another –  Ideal gases behave according to the Ideal Gas Law (PV =nRT) –  Air is NOT an ideal gas –  At standard temperature and pressure real gases (such as air) act similar to ideal gases The Ideal Gas Law: Rela.onships between Parameters •  Boyle’s Law:   P1V1= P2V2 •  Charles’ Law:   V1/T1 = V2/T2 •  Avogadro’s Law:   V1/n1 = V2/n2 Rela.onship between pressure and volume is indirect (as P increases, V must decrease) Rela.onship between volume and temperature is direct (as V increases, T must increase) Rela.onship between volume and moles is direct •  Gay‐Lussac’s Law:   P1/T1 = P2/T2 Rela.onship between pressure and temperature is direct The Ideal Gas Law •  These rela.onships (described by Boyle’s Law, Charles’ Law, Avogadro’s Law, and Gay‐Lussac’s Law) come together to form the Ideal Gas Law: PV = nRT •  •  •  •  P = pressure (atm) V = volume (L) n = quan.ty (mol) T = temperature (K) The Ideal Gas Constant (R) •  R is a constant, therefore it is the same regardless of the iden.ty of the gas (air or helium, etc) •  R can be solved for using the Ideal Gas Law: •  R has different values depending on the UNITS used in the ideal gas law (rearranged above): OR Direct Rela.onships •  Y is directly propor.onal to X •  Real Life Example –  X = price of gas –  Y = cost to fill car with gas –  When has is more expensive, it takes more money to fill your tank •  Graphs of Direct Rela.onships: –  Graph of y vs. x is linear –  y/x = a constant value (k) 14 Independent Variable (Y) –  This means when the independent variable (X) increases, the dependent variable (Y) also increases Graph of a Direct Rela;onship 12 y =k*x 10 8 6 4 2 0 0 2 4 6 8 10 12 Dependent Variable (X) 14 Inverse Rela.onships •  Y is inversely propor.onal to X •  Real Life Example –  X = # of people in a room –  Y = cost of hotel room per person –  The more people sharing a hotel room, the less each has to pay •  Graphs of Direct Rela.onships: –  Graph of y vs. 1/x is linear –  Y*x = a constant value (k) Graph of an Inverse Rela;onship Independent Variable (Y) –  Y is propor.onal to 1/X –  (Dependent variable is propor.onal to the inverse of the independent variable) 14 12 y =k/x 10 8 6 4 2 0 0 2 4 6 8 10 12 14 Inverse of Dependent Variable (1/X) Data Analysis of this Experiment: •  Determining the Gas Constant (R): PV=nRT Determine R from P, V data Determine R from P, T data Use a linear fit and the equa.on of a line to solve for R– do not use individual values! •  Remember: •  •  •  •  How Many Moles of Air? Molar Mass of Air Air Density is temperature dependent; ‐Use Value obtained from T (in Celcius) vs. density (in g/L) data, then convert to g/mL and use in the equa.on above Inves.ga.ng Boyle’s Law (P,V) •  Change V and measure P –  Pressure sensor connected to computer •  n, R, and T are held constant •  Monitor pressure as volume is changing •  Determine the Rela.onship (direct or inverse?) –  Graph P (y) vs. V (x) –  Graph P (y) vs. 1/V (x) –  Which Graph is linear? Determining R from Boyle’s Law (P,V) Data: Inves.ga.ng Gay‐Lussac’s Law (P,T) •  Change T and measure P –  Pressure sensor connected to computer •  n, R, and V are held constant •  Monitor pressure as temperature is changed •  Determine Rela.onship (direct vs. indirect) –  Graph P (y) vs. T (x) –  Graph P (y) vs. 1/T (x) –  Which is linear? Determining R from Gay‐Lussac’s Law (P,T) Data: Determining Absolute Zero •  Absolute Zero = the temperature of a gas when it is at a pressure of zero atm •  Zero Temperature Zero Pressure •  To obtain Absolute Zero value in your data: –  Plot T in Celsius (y) vs P in atm (x) –  Use a linear fit to find equa.on of line –  Extrapolate to find T at P = 0 atm (aka the value of the y‐intercept is the absolute zero value) •  Compare to literature –  Note: Absolue Zero is NOT zero degrees Celsius! Summary •  By the end of this lab you should accomplish the following: –  Determine if P,V and P,T rela.onships are direct or linear using graphical analysis (which graphs are linear?) –  Determine the gas constant (R) for P, V AND P, T data (compare) –  Determine the absolute zero for your gas ...
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This note was uploaded on 02/06/2010 for the course CHEM 102L taught by Professor N/a during the Spring '07 term at UNC.

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