General Chemistry I Exam III Practice Question Points Possible Points Earned 1 2 3 4 5 6 20 15 25 15 15 10 Total Score a Using the list of reactions and their enthalpy values calculate the H of the following reaction Question 1 C s O2 g CO2 g SrO s CO2 g SrCO3 s 2SrO s 2Sr s O2 g 2SrCO3 s 2Sr s 2C s 3O2 g H 234 kJ mol H 1184 kJ mol H 2440 kJ mol b If 10 3 grams of carbon react with 37 8 grams of oxygen gas to form carbon dioxide how much heat will be released Question 2 a Using the table below calculate the Hrxn for the combustion of propane C3H8 g 5O2 g 3CO2 g 4H2O l Substance Hf kJ mol CO2 g H2O g H2O l C3H8 g CH4 g 393 5 241 8 285 8 103 9 74 85 b Suppose that a 20 0 gram sample of propane is burned and all of the heat released by this reaction is absorbed by a 10 0 kilogram piece of iron If the initial temperature of the iron is 23 0 C and the specific heat of iron is 0 444 J g C what would the final temperature of the metal be Question 3 A specific laser operates at a power of 300 mW and produces photons with a wavelength of 425 nm a Calculate the frequency of the laser b Calculate the energy in Joules of a single photon c How long in s must the laser run in order to increase the temperature of 50 0 grams of water by 12 C The specific heat of water is 4 184 J g C d How many moles of photons were produced by the laser during this time Question 4 Lauric acid is commonly used in the production of soaps and other cosmetics The specific heat of lauric acid is 1 80 J g C and its heat of fusion is 0 183 kJ g a How much heat must be added to a 25 0 gram sample of lauric acid initially at 21 0 C to completely melt it at 43 8 C b Given the following information calculate the heat of sublimation for lauric acid C12H24O2 s C12H24O2 l H 36 6 kJ mol C12H24O2 g C12H24O2 l H 88 8 kJ mol Question 5 a Calculate the energy in Joules of the photons emitted when an electron of a hydrogen atom transitions from n 2 to n 1 RH 2 18x10 18 J The photons described above are used to irradiate a sheet of potassium Given that 1 eV 1 602x10 19 J 2 3 eV and me 9 11x10 31 kg answer the following b What is the velocity of the electrons produced by this irradiation process c What is the de Broglie wavelength in pm of these electrons a List all of the possible quantum numbers for n 5 Question 6 b What is the total number of orbitals associated with n 6
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