Gas Laws Advanced Problem Solving

Visit: Log in and select Chem 1A. When prompted, type the word of the day: tougher Ensure when asked if you will share your location you select “allow”. Visit: Sign in MasteringChemistry account name When prompted, type session ID: Please turn off all downloads. You can usually pause them by clicking on them and clicking pause. Facebook and youtube are officially banned during class time (this is not me micromanaging, it’s a legit internet issue as told to me by OIT). Remember back 5 rows of even side are no seating zones Visit: Word of the day: tougher LearningCatalytics: session ID:

SURVEY QUESTIONS How to know what specific formulas to use for specific gas law problems Use PV=nRT if only one set of conditions are given, in which case nothing cancels. Use ratio form, if two sets of conditions are given. Cancel anything that is constant. Will we has problems that use limiting reagents and ideal gas laws? Will the final contain ideal gas law problesm? Absolutely and yes. The final will contain everything. A myriad of questions about conversions between moles and grams, mol ratios, and using chemical reactions for mol ratios. Please come see me/ Paul/ Tutors in office hours. Do we need to know {insert whatever conversion you are wondering about here}? No, they are on the front page of the exam equation sheet that you already have. Visit: Word of the day: tougher LearningCatalytics: session ID:

DALTON’S LAW Dinitrogen oxide gas was generated from the thermal decomposition of ammonium nitrate and collected over water. The wet gas occupied 126 mL at 21 C when the atmospheric pressure was 755 Torr. What volume would the same amount of dry Dinitrogen oxide have occupied if collected at 755 Torr and 21 C. The vapor pressure of water is Torr at 21 C. Hint 1: If the total pressure is 755 Torr, what is the pressure of N 2 O? Hint 2: How do you determine the volume of a gas at a new pressure? Visit: Word of the day: tougher LearningCatalytics: session ID:

REACTIONS: SINGLE GAS PRODUCT Suppose that mL of propane gas C 3 H 8 at 1.00 atm and 298K is mixed with 1.00 L of oxygen gas at the same pressure and temperature and burned to form carbon dioxide gas and liquid water. Determine the final volume of the reaction mixture at 2.00 atm and 298 K if the reaction goes to completion. (note: volume of liquid water is negligible). Hint1: Write out the equation and balance it. Balance Carbons and Hydrogens first then oxygens. 1C 3 H 8 :5O 2 mol ∝ V mol ratio= volume ratio (At constant temp/pressure) Visit: Word of the day: tougher LearningCatalytics: session ID:

You may fill in and solve OR Pressure doubles, so volume……. Halves Volume=300.mL REACTIONS: Suppose that mL of propane gas C 3 H 8 at 1.00 atm and 298K is mixed with 1.00 L of oxygen gas at the same pressure and temperature and burned to form carbon dioxide gas and liquid water. Determine the final volume of the reaction mixture at 2.00 atm and 298 K if the reaction goes to completion. (note: volume of liquid water is negligible). Hint 2: Check for any limiting reagents, which may leave some gaseous reactant unreacted. 1C 3 H 8 : 5O 2 mol ∝ V mol ratio= volume ratio (At constant temp/pressure) 200.0mL of propane requires 1.00L of O 2 We have exactly that, no excess reagent, reaction goes to C 3 H 8 =O 2 =0atm You could solve for moles of CO 2 here, but that would be a lot of calculations and a lot of time/possibilities for mistakes. Instead look for how much volume would be made at the SAME temp and pressure, and then alter it for the new temperature and pressure. Short way: more thinking, more logic jumps, less math Visit: Word of the day: tougher LearningCatalytics: session ID:

REACTIONS: SINGLE GAS PRODUCT Suppose that mL of propane gas C 3 H 8 at 1.00 atm and 298K is mixed with 1.00 L of oxygen gas at the same pressure and temperature and burned to form carbon dioxide gas and liquid water. Determine the final volume of the reaction mixture at 2.00 atm and 298 K if the reaction goes to completion. (note: volume of liquid water is negligible). Long way: less thinking, less logic jumps, more math Same mol created. Both are used up! 0.245mol CO2 created! Visit: Word of the day: tougher LearningCatalytics: session ID:

REACTIONS: The reaction of solid dimethylhydrazine, (CH 3 ) 2 N 2 H 2, and liquefied dinitrogen tetraoxide, has been investigated as a rocket fuel; the reaction produces gaseous carbon dioxide, nitrogen and water vapor, which are ejected as exhaust gases. In a controlled experiment solid dimethylhydrazine reacted with excess nitrogen tetroxide with a final pressure of 2.50 atm, with a temperature of 400.0K. Find the pressure of each gas. Type the total pressure into learning catalytics. Hint: Write out and balance the equation. Hint2: what do you think must be true of the ratio of the gases pressures? Remember n ∝ P They must equal the mole ratios coefficients: 4 H 2 O: 2 CO 2 : 3N 2 Hint3: What is the total pressure? What are the mol ratios of products? H 2 O=(4/9)*(2.50 atm)=1.11atm CO 2 =(2/9)*(2.50 atm)=0.556 atm N 2 =(3/9)*(2.50atm)=0.834 atm H2OH2O CO 2 N2N2 Visit: Word of the day: tougher LearningCatalytics: session ID:

A 1.00 L sample of chlorine gas at 1.00 atm and 298 K reacts completely with 1.00 L of nitrogen gas and 2.00 L of oxygen gas at the same temperature and pressure. There is a single gaseous product, which fills a 2.00L flask at 1.00 atm and 298 K. Use this information to determine the following characteristics of the product. A) its empirical formula, B) its molecular formula, C) the most favorable Lewis structure based on formal charge arguments (the central atom is an N atom); d) the molecular shape. Hint 1: (a)“reacts completely” in this question means no limiting reagent, everything reacts all the way to zero. Hint 2: (a) Remember V ∝ n at constant pressure. Also don’t forget the reactants are diatomic gases. Hint 3: (b) You know P, V, T of the final reaction flask, what is n?, what mass of reactants were put in? Where did all those reactants go. What is the units of molecular mass? Ratio of gas moles=ratio of gas volume: 1Cl 2 :1N 2 :2O 2 Then Turn into g using molar mass To find total grams: do the following for each reactant: Plan: find total grams, find total moles. Do grams/moles. To find final total moles: use ideal gas law for final reaction flask. A) B) Visit: Word of the day: tougher LearningCatalytics: session ID:

A 1.00 L sample of chlorine gas at 1.00 atm and 298 K reacts completely with 1.00 L of nitrogen gas and 2.00 L of oxygen gas at the same temperature and pressure. There is a single gaseous product, which fills a 2.00L flask at 1.00 atm and 298 K. Use this information to determine the following characteristics of the product. A) its emperical formula, B) its molecular formula, C) the most favorable Lewis structure based on formal charge arguments (the central atom is an N atom); d) the molecular shape. Find total g Put in by doing each reactant separately: 1.15g+2.90g+2.62g=6.67g total Visit: Word of the day: tougher LearningCatalytics: session ID:

MORE REACTIONS: (I’m not sure we’ll make it to this one, if we don’t the answer will be posted online) A 1.00 L sample of chlorine gas at 1.00 atm and 298 K reacts completely with 1.00 L of nitrogen gas and 2.00 L of oxygen gas at the same temperature and pressure. There is a single gaseous product, which fills a 2.00L flask at 1.00 atm and 298 K. Use this information to determine the following characteristics of the product. A) its emperical formula, B) its molecular formula, C) the most favorable Lewis structure based on formal charge arguments (the central atom is an N atom); d) the molecular shape. Ratio of gas moles=ratio of gas volume: 1Cl 2 :1N 2 :2O 2 Total Mass (from other slide) =6.67g total Total Moles reactant: Compare to mass of NClO 2 = = 81g/mol= same, so NClO 2 is also the molecular formula Visit: Word of the day: tougher LearningCatalytics: session ID:

A 1.00 L sample of chlorine gas at 1.00 atm and 298 K reacts completely with 1.00 L of nitrogen gas and 2.00 L of oxygen gas at the same temperature and pressure. There is a single gaseous product, which fills a 2.00L flask at 1.00 atm and 298 K. Use this information to determine the following characteristics of the product. A) its emperical formula, B) its molecular formula, C) the most favorable Lewis structure based on formal charge arguments (the central atom is an N atom); d) the molecular shape. Why can’t we add another double bond to minimize formal charge further? Steric number 3: trigonal planar. Visit: Word of the day: tougher LearningCatalytics: session ID: