1 2 3 4 5 6 7 10 Name Section GENERAL CHEMISTRY I EXAM 4 FALL 2015 Question Points Possible Points Earned 15 15 15 20 15 20 20 Total 1 The following reaction is the reduction of zinc in the presence of a strong acid Zn s 2H aq Zn2 aq H2 g a Calculate the work done in J if 35 grams of zinc react with excess acid at STP b If the system releases 102 J of heat while the gas is forming what is the change in internal energy U c The same reaction is performed in the vacuum of space Would the work done be greater than less than or equal to the work done when at STP 2 When burning hydrocarbons efficiency is determined in part by comparing the heat released per mole of carbon dioxide formed assuming one mole of fuel Based on this definition determine which fuel is more efficient between propane and butane Propane C3H8 5O2 3CO2 4H2O Butane 2C4H10 13O2 8CO2 10H2O Substance Hf kJ mol Propane Butane Carbon Dioxide Water 103 85 147 6 393 5 285 8 3 A 325 mW laser produces photons with a wavelength of 557 nm a Calculate the energy of a single photon produced by the laser in J b Calculate the number of moles of these photons required to heat 200 mL of water from 10 1 C to 13 2 C The specific heat of water is 4 184 J g C c Given that 1 W 1 J s calculate the time in seconds it takes for the laser to complete the heating process d Given that visible light has wavelengths between 400 and 700 nm and red light has the lowest energy of all colors approximate the color of light emitted by the laser Hint ROYGBIV 4 A hydrogen atom is energized with electricity so that its electron is excited to n 5 a Calculate the wavelength in nm of the photons emitted when the electron drops to the n 2 state b Suppose that the hydrogen atom is ionized and the electron leaves its orbitals at a velocity of 3 65x106 m s What is the de Broglie wavelength in nm of the electron The mass of an electron is 9 11x10 31kg c Which is a greater change in energy an electron transitioning from n 3 to n 2 or n 5 to n 4 5 Lead is a heavy metal element with atomic number 82 a Write the full electron configuration for a lead atom in the ground state b Lead has a common oxidation state of 2 Write the abbreviated electron configuration for the Pb2 ion c What is the set of quantum numbers n l ml ms that describe the 31st electron in a lead atom s orbital diagram Assume a ground state electron configuration d Lead can be considered a multi electron atom Which orbital has the greatest energy 4f 5d or 6s 6 Quantum numbers are essentially numerical representations of electrons within the orbitals of an atom and are the foundation of modern quantum mechanics a How many orbitals are associated with n 5 b How many electrons are associated with n 5 and ml 0 c How many orbitals are associated with n 5 l 2 and ml 0 d List all of the possible values of l ml and ms when n 4 e Explain why 4 0 1 1 2 is an impossible set of quantum numbers 7 Explain the following a The atomic radius of Na Cs b The atomic radius of Ca Br c The ionic radius of K Cl 8 Explain the following a The first ionization energy of Be Ba b The first ionization energy of I Sr c The first ionization energy of N O d An atom s second ionization energy is always greater than its first 9 Explain the following a The electron affinity value for N F b The electron affinity value for Zn 0 10 Explain the following a The electronegativity of O N
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