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Data Table Needed

Data Table Needed. Standard Heats of Formation. Problem Set. Applications of Thermodynamics. Enthalpy Changes and Thermodynamic Applications. Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology. Thermodynamic Applications. Reading Assignment:

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Data Table Needed

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  1. Data Table Needed Standard Heats of Formation Problem Set Applications of Thermodynamics

  2. Enthalpy Changes and Thermodynamic Applications Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

  3. Thermodynamic Applications • Reading Assignment: • Chang, Chapter 6.7, 9.10 • Hess’ Law is used to calculate the heat released by a chemical reaction. • Applications of thermodynamic principles

  4. Enthalpy Heat energy content of a molecule internal molecular motion electronic energy H = E + PV pressure-volume work required to maintain the volume of the molecule Only defined for a constant pressure process

  5. Enthalpy Values Absolute enthalpy values cannot be measured, but changes in enthalpy can be measured relative to an arbitrary reference state

  6. EnthalpyHeat of Formation Values CH3OH(l) DHfº=-238.66 kJ·mol-1 H2 (g) DHfº=-187.78 kJ·mol-1 Standard State O2 (g) H2O2(l) C(gr) DHfº=+78.53 kJ·mol-1 Standard State C10H8(s) Reference State An element, molecule or ion at 25 ºC and 1 atm pressure An element in its most stable phase at 25 ºC and 1 atm pressure DHfº = 0

  7. standard state 25 ºC and 1 atm enthalpy formation change (final value - initial value) Enthalpy of Formation DHfº What do the initial and final values refer to? Is enthalpy a function of temperature?

  8. 3/2 O2(g) O3(g) O2(g) O2(g) C(gr) + 2 H2(g) CH4(g) Enthalpy of FormationExamples DHfºat 25 ºC and 1 atm for one mole of oxygen: DHfº= 0 ozone: DHfº= +142.7 kJ·mol-1 methane: DHfº= -74.81 kJ·mol-1 Which of the reactions is exothermic?

  9. HCHO(g) C(dia) KBr(s) Write the equation and determine theenthalpy of formation at 25 ºC and 1 atm forone mole of formaldehyde: C(gr) + H2(g) + 1/2 O2(g) DHfº= -108.57 kJ·mol-1 diamond: C(gr) DHfº= +1.897 kJ·mol-1 potassium bromide: DHfº= -392.17 kJ·mol-1 K(s) + 1/2 Br2(l)

  10. C(gr) + O2(g) CO2(g) C(gr) + 1/2 O2(g) CO(g) CO(g) + 1/2 O2(g) CO2(g) Enthalpy of Reaction DHfº = -110.52 kJ·mol-1 DHfº = -393.51 kJ·mol-1 What does a negative enthalpy change indicate? Can carbon monoxide burn exothermically? DHrxº = ?

  11. Hess' Law Elements +DHf,products - DHf,reactants DHrx Reactants Products DHrx = S DHf,products - SDHf,reactants

  12. Hess' Law C(gr) + O2(g) DHrx CO(g) + 1/2 O2(g) CO2(g) DHrx = S DHf,products - SDHf,reactants DHrx = [DHf,CO2 ] - [DHf,CO + 1/2 DHf,O2 ] = [-393.51 ] - [-110.52+ 1/2·0] = -282.99 kJ ·mol-1

  13. Enthalpy of ReactionHess’ Law During the winter, a typical house will require about a half million kilojoules per day for heating. How many moles of natural gas (methane) would be needed? Is there an advantage to produce liquid water or steam as a by-product?

  14. Acetylene Determine the heat released when one pound (454 g) of acetylene is burned. To obtain a "hotter" flame, oxygen is often burned with acetylene. Why is the flame hotter?

  15. PropaneC3H8 • The standard heat of combustion of gaseous propane to make liquid water is -2220. kJ·mol-1 • Determine the standard heat of formation of gaseous propane. • How much pressure-volume work is involved when this reaction occurs at 25 °C? • Determine the change in internal energy for this reaction. • The heat flow in this process is equal to which thermodynamic term, qp or qv?

  16. Enthalpy of Neutralization Estimate the enthalpy of neutralization of aqueous sodium hydroxide and hydrochloric acid. (Literature value: -60.2 kJ·mol-1)

  17. Thermite Reaction The Thermite Reaction has been used as a method to weld together railroad rails. It involves a single displacement reaction in which iron(III) oxide is burned with aluminum powder. How much energy is released by this process?

  18. Thermodynamic ApplicationsComparison of Liquid Fuels • methanol • ethanol • isooctane

  19. Adiabatic Expansion • The same process occurs, except there is no heat flow allowed between the system and the surroundings. • On expansion, the gas will cool and follows a non-isothermal PV curve. • PVg = constant • for an ideal diatomic gas, g =1.67

  20. Adiabatic Expansion • In each of the examples, a different pressure change pathway is followed by the gas. • How much work will be done if the process is reversed to complete the cycle?

  21. Carnot Cycle • Consists of two isothermal and two adiabatic steps, occurring alternatively. • One of each type of step is involved in compression and expansion.

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