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MSU CEM 142 - Exam 1 Study Guide

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CEM 142 1st EditionExam # 1 Study Guide Chapter 5 and 6—Exam 1Intermolecular forces and bonds•Similarities:1) Both involve attractions2) Both require energy to be overcome3) Both release energy when formed•Differences:1) Attractions between bonds include electrons from one atom and protons of another atom2) Attractions between intermolecular forces (IMFs) include one end of a dipole to the other3) When bonds break, new species are formed4) When IMFs break, the same species are still present. It is usually a phase change.•Bonds are stronger than IMFsTypes of Intermolecular Forces•London dispersion forces1) Temporary fluctuating dipoles2) Present in ALL substances3) For non-polar molecules, LDF is the only force present4) Strength of force depends on size, surface area, and shape of molecule•Dipole-dipole1) Present in polar substances2) Stronger than LDF•Hydrogen bonding1) Present in compounds with hydrogen covalently bonded to nitrogen, oxygen, or fluorine (bond is highly polarized—charge separated)2) Stronger interactions between moleculesMolecular structure properties1. Draw the Lewis structure2. Determine the molecular shape (from VSEPR)3. Determine the bond polarities (difference in electronegativity)4. Determine molecular polarity (adding up the bond polarity vectors)5. Determine what type of IMFs are present6. Determine how the molecules might interactState FunctionsAt constant pressure thermal energy q (thermal energy change) is a state function, enthalpy q= HΔ•Enthalpy: Heat absorbed or emitted•Endothermic reaction: Heat INTO the system from the surroundings; HΔ = (+)•Exothermic reaction: Heat OUT of the system to the surroundings; HΔ = (-)Entropy•Measure of number of possible arrangements for a given state•When arrangements increase, the higher the probability of that state•Energy will transfer from a hot block to a cold block because it is more probable-Energy is transferred in quantums (certain packets of energy).-Causes the cold block to increase its kinetic energy-More possibilities when the energy is spread outThermodynamics1) Energy cannot be created nor destroyed. You cannot get more energy back than what you started with2) For any change the total entropy of the universe (not the system) must increase, some energy is always lost  SΔTotal = SΔsystem + SΔsurroundings3) The entropy of a perfect crystal at absolute zero is zero•Mixing: When mixing dye and water, the dye cannot unmix. This is because there are more arrangements when it is mixed than when it is unmixed.-If the total entropy increases, the process will happen (vise versa)Gibbs Free Energy•A proxy for measuring total entropy change GΔ ; expressed in terms of the system only, not the surroundings!• G tells about what energy is left and available to do workΔG = HΔ Δsystem - T SΔsystem* The temperature (T) will always be positive* When G = 0, the rate of the reaction will reach equilibrium, capable of going Δbackwards or forwards0 = H – T S Δ Δ  H = -T SΔ ΔSOLUTIONS•Solutions: A homogenous mixture of two or more components•Solvent: Major component of solution (mostly liquid)•Solute: Minor component (mostly solid)Solubility•Factors that affect solubility:1) Polarity2) Temperature (kinetic energy/collisions/mixture)3) Nature of solvent (IMFs/bonds)4) Nature of solute (IMFs/bonds)5) Entropy change •All molecules must break their IMFs in order to form new bonds*If polarity increases, solubility increases*If temperature increases, solubility increaseSolution Stoichiometry•Units: 1) Molarity (mol/L)-1M solutions contains 1 mol of solute dissolved to make 1L of solution2) g/mL3) Percent4) ppm (10x10-6g per gram)5) ppb (10x10-9g per gram)•Saturated: Maximum amount of solute dissolved (you can tell depending on where you add more if it will dissolve or not, it should not dissolve if saturated)•Unsaturated: If you add more solute, it will dissolve•Miscible: The solute and solvent mix up to form solution•Immiscible: The solute and solvent cannot form


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