Thermochemistry vs Visualizing Organic Chemistry

Thermochemistry helps in evaluation of enthalpy or heat release/absorption of a system undergoing numerous temperature changes and phase transitions. The calculations take advantage of known values of heat capacity at constant pressure (Cp) and molar or per gram enthalpy of phase transition. Amount of compound can be defined in grams or moles, in a way that Cp and enthalpy units would match. App provides enthalpy values for each step. Negative enthalpy points to exothermic process – heat release, while positive one to endothermic - heat absorption. °C and K are interchangeable. Calorimetry section provides means for evaluation of the heat capacity of calorimeter and for finding equilibrium temperature of mixed system. Forward arrow button sets the final temperature of the mixture. Backward arrow button sets missing temperature or heat capacity of one of the components. Enthalpy values show heat flow for each component. Example of problems solved by application (screenshots): Problem 1: Calculate the amount of energy required to change 100.0 g of ice at -15.0 °C to steam at 125.0 °C. Known values: Heat of melting = 334.16 J g¯1 Heat of vaporization = 2259 J g¯1 specific heat capacity for solid water (ice) = 2.06 J g¯1 K¯1 specific heat capacity for liquid water = 4.184 J g¯1 K¯1 specific heat capacity for gaseous water (steam) = 2.02 J g¯1K¯1 Solution: 1) Heating of 100.0 g of ice from -15.0°C to 0.0°C: (100.0 g) (15.0 K) (2.06 J g¯1 K¯1) = 3090 J 2) Melting of 100.0 g of ice: (100.0 g) (334.16 J g¯1) = 33416 J 3) Heating of 100.0 g of liquid water from zero to 100.0 Celsius: (100.0 g) (100.0 K) (4.184 J g¯1 K¯1) = 41840 J 4) Evaporations of 100.0 g of liquid: (100.0 g) (2259 J g¯1) = 225900 J 5) Heating of 100.0 g of steam from 100.0 to 125.0 Celsius: (100.0 g) (25.0 K) (2.02 J g¯1 K¯1) = 5050 J 6) Summation of the results: 3090 + 33416 + 41840 + 225900 + 5050 = 309.3 kJ Problem 2: Determine the heat capacity of a coffee-cup calorimeter. During calibration 100.0 g of water at 58.5 °C has been added to 100.0 g of water, already in the calorimeter, at 22.8 °C. Calculate the heat capacity of the calorimeter in J/°C, if final temperature of the water is 39.7 °C. (Specific heat of water is 4.184 J/g °C.) Solution: 1) Heat given up by warm water: q = (100.0 g) (18.8 °C) (4.184 J/g °C) = 7865.92 J 2) Heat absorbed by water in the calorimeter: q = (100.0 g) (16.9 °C) (4.184 J/g °C) = 7070.96 J 3) The difference was absorbed by the calorimeter: 7865.92 - 7070.96 = 794.96 J 4) Calorimeter constant: 794.96 J / 16.9 °C = 47.0 J/°C Problem 3: Determine the final temperature when 10.0 g of aluminum at 130.0 °C mixes with 200.0 grams of water at 25.0 °C. Please note the starting temperature of the metal is above the boiling point of water. In reality, the sample may vaporize a tiny amount of water, but we will assume it does not for the purposes of the calculation. Solution: 1) The colder water will warm up and the warmer metal will cool down. The whole mixture will equilibrate up at the same temperature. The energy which "flowed" out of the warmer metal equals the energy which "flowed" into the colder water: Qaluminum = Qwater (10) (130 - x) (0.901) = (200.0 )(x - 25) (4.18) 117.13 - 0.901x = 83.6x - 2090 x = 26.12 °C. Important! Water didn’t cross temperature of phase transition – vaporization; otherwise calculation would be more complex. Calculation of reaction standard Gibbs free energy: For the general reaction aA + bB -> cC + dD ΔG°rxn = cΔGf°(C) + dΔGf°(D) - aΔGf°(A) - bΔGf°(B) Example: Calculate the Gibbs free energy for the following reaction at 25 °C. Cu (s) + H2O (g) -> CuO (s) + H2 (g) ΔG°rxn = ΔGf°(CuO (s)) – ΔGf°(H2O (g)) = (–129.7 kJ/mol) – (–228.6 kJ/mol) = 98.9 kJ/mol ΔGf° = 0; for elements in their standard state by definition. At equilibrium, ΔG = 0! Important points Application uses dot as a decimal separator. Special attention should be paid for units’ consistency.

Visualizing Organic Chemistry is a collection of tools that make learning organic chemistry easier. It’s an excellent resource for instructors and students alike! The app contains over 60 visuals, most incorporating 3D interactive models and animations that help students envision key concepts in organic chemistry. Visualizing Organic Chemistry includes: -Orbitals and Bonding- • Interactive 3D models of basic and hybrid atomic orbitals • Molecular orbital diagrams with 3D models showing orbital shape and symmetry • How bond dissociation energy changes with internuclear distance -Physical Properties- • Define the most important functional groups with structural drawings and 3D models • Electronegativity trends and Pauling electronegativities of the elements • 3D electrostatic potential maps demonstrating charge distribution in molecules • 3D molecular models demonstrating how molecular size and shape affect surface area and boiling point -Free Rotation and Conformations- • Interactive Newman projections demonstrating free rotation with conformational changes reflected in 3D models • Interactive Newman projections demonstrating torsional and steric strain energies • 3D models of smaller cycloalkanes with animated changes between important conformations • 3D models of cyclopropane, cyclobutane, and cyclopentane illustrating several important conformations • Animated 3D models of cyclohexanes demonstrating conformational inversions (chair flips) and 1,3-diaxial strain • 3D models illustrating spirocyclic, fused, and bridged bicyclic compounds -Stereochemistry- • 3D models illustrating cis/trans isomers of disubstituted rings and alkenes • 3D models demonstrating chirality and its relation to symmetry • 3D models depicting the spatial relationships of substituents in both dash-wedge and Fischer projections • Interactive dash-wedge and Fischer projections demonstrating 3D rotation of substituents in 2D space • 3D model of a basic polarimeter illustrating the measurement of optical rotation of chiral compounds • 3D models that demonstrate enantiomeric and diastereomeric relationships in compounds with more than one chiral center -Spectroscopy- • Animated, interactive 3D models depicting CH2X2 IR stretching and bending vibrational modes • IR spectra for several compounds depicting the most important functional group absorptions • NMR spectra with accompanying 3D models illustrating chemical equivalency and its relationship to symmetry • Proton and carbon-13 NMR spectra for several compounds depicting several important chemical shift ranges -Reactions- • Interactive 3D animation of HX addition showing free energy changes during the reaction • Interactive 3D animations demonstrating syn/anti stereoselectivity in various electrophilic additions • Interactive 3D animation of nucleophilic substitutions showing free energy changes during the reaction • Interactive 3D animations demonstrating inversion and retention of stereochemistry in nucleophilic substitutions • Interactive 3D animations demonstrating syn/anti stereoselectivity in E1 and E2 eliminations