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University of Missouri - Columbia
CHEM 1320

LEARNING OBJECTIVES FOR CHEMISTRY 1320 EXAM 1 Chapter 6 2 • Kinetic energy = E k mv /2 • Potential energy, E p • Internal energy E= E k E ; p • Heat, q • Work, w o one example is PV work: w = -P ΔV ext • Enthalpy, H o enthalpy is the heat for a process (e.g., reaction) performed at constant pressure o formally, enthalpy is defined as H=E+PV • Joule = kg-m /s 2 • Sign conventions for heat and work o heat > 0 means heat is absorbed by the system (endothermic) o heat < 0 means heat is emitted by the system (exothermic) o work > 0 means surroundings does work on the system o work < 0 means system does work on the surroundings • Be able to draw enthalpy diagrams for reactions • Three kinds of, closed isolated st • 1 law of thermodynamics (energy is conserved) o ΔE=q+w o ΔE sys+ ΔE surr 0 • State functions (E, H, V, P, T, Ep, Ekand others) • What is a state function? • Bomb calorimeter (constant volume) • Constant pressure calorimeter (the kind used in lab) • Calorimetry equations o q rxn= -qcal o q = CΔT = msΔT • Know difference between specific heat and heat capacity o specific heat is intensive, heat capacity is extensive • ΔH =fheat change for formation of 1 mole of product from its constituent elements in their standard states at P=1atm and T=25C o ΔH = 0ffor element in standard state (e.g., O (g)2 Cu(s), C(graphite), S(rhombic) o Be able to write standard formation reactions 0 0 • Use ΔH dafa to calculate ΔH of a reaction o Sum of ΔH for froducts minus sum of ΔH for reactfnts properly multiplied by stoichiometric coefficients from balanced chemical reaction 0 • Use Hess’s law to calculate ΔH o If you reverse a reaction…change sign of ΔH o If you multiply a reaction by n…multiple ΔH by n • Power of Hess’s law: heat of solution ΔH solnan be understood using Hess’s law o ΔH refers to dissolving an ionic solid in water, such as NaCl(s) → Na (aq)+Cl (aq) soln o Build a conceptual 2-step pathway involving breaking the crystal lattice to produce gas phase ions, then dunk the gas phase ions in to water 1 § Step 1: NaCl(s) → Na (g)+Cl (g) ΔH =1U + - + - § Step 2: Na (g)+Cl (g)→ Na (aq)+Cl (aq) ΔH = ΔH 2 hydr o ΔH solnis the sum of the enthalpy changes for these two steps, i.e., ΔH soln U + ΔH hydr o U is the lattice energy. U is the energy required to break the ionic interactions that hold the crystal lattice of an ionic solid together. U is always positive. o ΔH hydris the heat of hydration. ΔH hydris a measure how much water likes to pack around ions in aqueous solution. ΔH hydris always negative. o ΔH solnis a balance between U + ΔH hydr § if ΔHsolnis exothermic, hydration outweighs lattice energy § if ΔH is endothermic, lattice energy outweighs hydration soln Chapter 7, sections 1-5 • Classical mechanics, i.e., Newton’s law, F=ma, governs macroscopic world • Quantum mechanics govern microscopic world
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