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CHEM 1109

CH109-04 Practice questions for Exam 2 Fall 2013 1. What is the root mean square speed of a hydrogen molecule at 22.00°C? 2. Calculate the frequency (in Hz) and wavelength (in nanometers) of the emitted photon when an electron drops from the n = 4 to the n = 2 level in a hydrogen atom. 1 3. A 25.00 L steel balloon contains 21.05 g of Ne, 5.038 g of He, and 10.65 g of Xe. a. Determine the mole fraction of each gas in the balloon. b. Determine the partial pressures of each gas and the total pressure in the balloon at a temperature of 157°C. 2 4. a. Calculate H for the overall equation 4NO (g) + O (g2  2N O 2s) given th2 i5formation below. 2N O2(5)  4NO(g) + 3O (g) 2 H = 447.4 kJ/mol 2NO(g) + O (g)  2NO (g) H = -114.2 kJ/mol 2 2 b. Is the overall reaction exothermic or endothermic? 3 5. A 3.000 g piece of aluminum foil at a temperature of 4.56°C is added to 78.93 mL of water at 59.95°C in a coffee cup calorimeter. Given the information below, determine the final temperature of the water. Specific heat of aluminum: 0.900 J/(g·°C) Specific heat of water: 4.184 J/(g·°C) Density of water: 1.000 g/mL 6. As shown below, H for the dissolution of ammonium chloride in water is 14.78 kJ/mol. When ammonium chloride is dissolved in water do you expect the water to get warmer or colder? Explain your answer. 4 7. Give the electron configuration and draw the orbital diagram for each atom or ion (do not use abbreviations with a noble gas “core”). Also determine if the species is diamagnetic or paramagnetic. An example is given for hydrogen below. 1 Example: Hydrogen (H) Electron configuration: _______1s ______________________ Orbital diagram: Diamagnetic or paramagnetic ? a. Silicon Electron configuration: ________________________________ Orbital diagram: Diamagnetic or paramagnetic ? b. Sulfide Electron configuration: ________________________________ Orbital diagram: Diamagnetic or paramagnetic ? 5 c. Manganese(Mn) Electron configuration: ________________________________ Orbital diagram: Diamagnetic or paramagnetic ? d. Manganese(III) (Mn ) Electron configuration: ________________________________ Orbital diagram: Diamagnetic or paramagnetic ? 8. Under particular conditions, it takes 2.00 moles of HCl gas 43.0 seconds to effuse through a porous membrane. Under identical conditions, how long would it take for 1.00 mole of NH 3as to effuse? 6 9. Determine the enthalpy of reaction for the hydrogenation of acetylene to form ethane, o C2H 2g) + 2H (2)  C H 2g)6 H rxn= ? From the following data: o 2C 2 2g) + 5O (2)  4CO (g) 2 2H O(l) 2 H rxn= -2600. kJ/mol 2C H (g) + 7O (g)  4CO (g) + 6H O(l) H o = -3120. kJ/mol 2 6 2 2 2 rxn o H 2g) + ½O (2)  H O(l2 H rxn= -286 kJ/mol 7 10. Ammonium sulfate reacts with calcium chloride to form a precipitate as shown below. a. Determine the products that are formed and give the balanced complete (molecular) chemical equation below. b. What is the balanced net ionic equation for the reaction of potassium hydroxide with phosphoric acid? o o c. Use the table of Heats of Formation ( H f) at the end of the exam to determine H for the balanced reaction you gave in part b above. d. Is the reaction exothermic or endothermic? 8 e. What is H if the reaction on the previous page is performed with 54.3 mL of a 1.37 M solution of (NH )4 2 a4d excess CaCl ? 2 9 You will be given the following Useful Information on the exam: Equations: ( F32) m K = °C + 273.15 °C = d  1.8 V molesofsolute M 1 1 M V 2 2 M = litersofsolution PV = nRT n 3RT χa= a Pa= χa· Ptotal urms= ntotal Μ  2 rateA  Μ B P a    V nb nRT rateB Μ A       E = E – E E = q + w q = C × T products reactants q = m × Cs× T qcalC ×cal w = -PV H o n H (products)-n H (reactants) rxn p f r f  = c E = h = hc  = h λ λ mν h  1   1 1  x × mv ≥ En= -2.18 x 10-18J 2  E = -2.18 x 10-18J 2 2  4  n  n f n i  Constants and definitions: Latm 1 mole = 6.022 x 10 entities 1
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