Problem Set 4 Use Hess's law to determine the change in enthalpy for the reaction 2C (s) + H2 C2H2 given the following reactions. a) C(s) + O2(g) CO2 b) H2(g) + O2(g) H2O(l) c) 2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(l) 2C(s) + 2O2(g) 2CO2 H2(g) + O2(g) H2O(l) 2CO2 + H2O C2H2 + 3/2 O2 = -393.5 KJ = -285.8 KJ = -2598.8 KJ = -787 KJ = -285.8 KJ = 1299 KJ = 226KJ Write the net ionic equation for the following reaction: BaCl2(aq) + Na2SO4(aq) BaSO4(s) + 2NaCl(aq) Ba2+ + SO42- BaSO4 Calculate the Enthalpy of reaction for the reaction of igniting propane (C 3H8) in air to produce carbon dioxide and water. O-H 460 KJ, C-O 351KJ, O-O 498 KJ C-C = 347 KJ, C-H = 414 KJ, H-H = 436 KJ (Hint: Make sure you write a balanced reaction) Bonds Broke Bonds Formed C-C (2 x 347) = 694 KJ O-H (8 x 460) = 3680 KJ C-H (8 x 41) = 3312 KJ C-O (6 x 2106) = 2106 KJ O-O Bonds Broke Bonds Formed = 710 KJ A pool that 7 ft wide, 10 ft. long, and 3 ft. deep is filled with water and is initially 10 oC. Obviously, this is much to cold to go for a swim, so the owner of pool decides to turn the heat of the pool up to 25oC. The fuel used as the heating source is propane (how fortuitous). Calculate how many grams of propane are needed to heat the pool up to the desired temperature. (Specific Heat of water = 4.184 J/g K). (Hint: use the heat of reaction you calculated in the previous problem) (7 ft x 10 ft x 3 ft)(12 in/1ft)3(2.54 cm/1in)3 = 5946537 grams Q = (5946537g)(4.184J/gK)(13.5K) Q = 335884240 J 335884240 J/ 710000 J = 473 moles of C3H8 = 20,815 grams Calculate the frequency (Hz) and wavelength (nm) of the emitted photon when an electron drops from the n=4 to the n=2 level in a hydrogen atom. (Use the formulas provided to you in your lecture notes.) Frequency = 6.17e14Hz Wavelength = 486 nm Same as on Problem Set 4.1 An electron in the hydrogen atom makes a transition from a higher energy state of principal quantum numbers ni to the n = 2 state. If the <a href="/keyword/photon-emitted/" >photon emitted</a> has a wavelength of 434 nm, what is the value of ni? E = ch/ [(3.0e8 m/s)x(6.634e-34 Js)]/434e-9m = 4.58 e -19 J E = RH(1/ni2 -1/nf2) 4.58e-19 J = -2.18e-18 J(1/x2 -0.25) -0.21009 = 1/x2 0.25 0.3991 = 1/x2 x=5 ni= 5 Quantum numbers deal with the angular momentum of electrons. Suppose an electron in an atom has a principal angular momentum quantum number of n = 3. List the possible values of l and ml that it can have. L = 2 , ml = 2....0....-2, l= 1, ml = 1...0...-1, l=0, ml = 0