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 •
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• 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: •
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• 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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 Spring '07
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