MSU CHEM 141 EXAM 2025

According to Valence Bond Theory, what types of orbitals does carbon use for bonding in diamond? - -The sp3 hybridized that form upon mixing s and p orbitals Why does graphite conduct electricity while diamond does not? - -Some of the valence electrons in graphite, but not in diamond, are delocalized in pi molecular orbitals that extend across the entire network, so electrons can move freely in these orbitals Which is likely to have the highest melting point? MgF2, MgBr2, or NaBr - -MgF2 What is the hybridization of the sulfur in SO3? - -sp2 What is the formal charge on the sulfur in SO3? - -+2 What is the most likely formula for the compound formed between aluminum and chlorine? - -AlCl3 What is the strongest bond/interaction that is overcome when the substance boils? - Covalent bonds Out of Ar, CH4, and N2, which one would have a Boltzmann distribution that is to left and high? - -Ar Imagine a system composed of two different types of molecules, one relatively light and one relatively heavy. At a particular temperature, which molecule has a lower kinetic energy? - -Both are the same On a humid day, water in the air condenses on the outside of a cold cup. Is the condensation of the water endothermic or exothermic? Why? - -Exothermic because the thermal energy is transferred from the surroundings to the system When sweat evaporated from your skin you feel cooler. What process is responsible for this? - -Energy transfers from your skin to the water AND the energy makes the molecules vibrate more strongly AND intermolecular forces between the water molecules are overcome and the water evaporates 10 g of substance A is placed in one beaker and 10 g of substance B is placed in a different beaker. They both have the same initial temperature. After the same amount of thermal energy was added to both substances, the temperature of substance B was higher. Which has the higher specific hear? - -Substance A CHM 141 CHM 141 A 58 g block of metal was heated to 200 C and added to 100 g of water at 25 C. As a result, the temperature of the water increased to 35 C. The specific heat of water is 4.184. What is the specific heat of the metal? - -.437 Ammonia reacts with carbon dioxide to produce urea and water: 2NH3 + CO2 = (NH2)2CO + H2O. How many molecules of carbon dioxide remain at the end of the reaction? - -1 Ammonia reacts with carbon dioxide to produce urea and water: 2NH3 + CO2 = (NH2)2CO + H2O. How many molecules of urea are produced? - -3 Ammonia reacts with carbon dioxide to produce urea and water: 2NH3 + CO2 = (NH2)2CO + H2O. If 5 g of ammonia reacts with excess carbon dioxide, how many grams of urea would be produced? - -8.82 g Atomic radius ________ from left to right across a row on the Periodic Table. Why? - Decreases because the relative attraction between the protons and the outer electrons increases As frequency increases, energy _________. - -Increases Why do we use an energy level diagram rather than the Bohr model of the atom to describe electron behavior in atoms? - -Energy level diagrams describe electron behavior of all elements but the Bohr model only describes electron behavior for Hydrogen AND the Bohr model doesn't take into account the wave-particle duality of electrons The minimum frequency to eject an electron from a piece of sodium metal is 4.4 x 10^14 Hz. If light with a wavelength of 825 nm is shone on the metal, what will happen? - -No electrons will be emitted. Shorter wavelength = _____________ frequency - -higher Higher frequency = _______________ intensity - -higher Yellow light has a wavelength of 580 nm. What is the energy of one photon of yellow light? - -3.4 x 10^-19 J Consider a proton and an electron both traveling 1/10th the speed of light. Which has a longer wavelength? - -The electron What is the electron configuration of a nitride ion N3- - -1s2 2s2 2p6 At the present time the number of atoms in the universe is.... - -Decreasing, because of nuclear fusion in the stars. (fusion - two atoms coming together to form a larger one) CHM 141 CHM 141 U-235 is most likely to spontaneously undergo: - -Nuclear Fission BECAUSE it has a large number of protons in the nucleus and the p-p repulsion makes it unstable AND breaking apart produces lighter more stable elements Two toxic substances react to make a new substance. What can you determine about the toxicity level of the new substance? - -You cannot determine if the new substance will be toxic or harmless. Consider Cl- and K+. Which is larger and why? - -Cl- because it has the same number of electrons as K+, but fewer protons, so the attraction between the electrons and the nucleus are weaker. Two elements X and Y are in the same row of the periodic table. X has a larger atomic radius than Y, what is true about their relative ionization energies and why? - -Y has a larger ionization energy BECAUSE electrons in Y are more strongly attracted to the nucleus Why do two hydrogen atoms interact through covalent bonds while two helium atoms do not? - -Because H2 has more electrons in the bonding orbitals than in the anti-bonding orbitals, whereas He2 has the same number in both. Which substance has the highest boiling point and why? F2 and Br2 - -Br2 BECAUSE Br2 has stronger LDF's than F2, and therefore takes more energy to overcome the LDF's when Br2 boils Why don't metals shine in the dark? - -Metals shine because they absorb and then re emit photons. In the dark, there are no photons to absorb. How much energy is released when an electron