Lec-04-Chap06-4

Lec-04-Chap06-4 - Lec-04-Chap06-4 Lec-04 Chemical...

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Lec-04-Chap06-4 9/9/2009 Standard Enthalpies of reaction Enthalpies of formation. Calorimetry, etc. 1 Lec-04: Chemical Thermodynamics Chapter 6 - Continued 1 Enthalpy Changes: Chemical Processes       22 -1 2 1 H g O g H O 241.8kJmo 2 l g H      Δ H reaction at 25 °C and 1 bar: standard enthalpies of reaction Δ H ° 2 Enthalpy , like energy , mass, and volume , is extensive .                 -1 -1 2 2 2 2 2 H g O g 2H O g 1 H g O g 2 reactio 48 n 1 3.6 H O g kJ m 241.8kJ mo ol reaction 2 2 l H H H H          For any given transformation: (initial) → (final) The reverse process is: (final) → (initial)             -1 1 2 - 2 241.8kJ mol 1 H O g H g O g 241.8k exothermic endothermi J mol 1 H g O 2 c g H O g 2 H H      
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Lec-04-Chap06-4 9/9/2009 Standard Enthalpies of reaction Enthalpies of formation. Calorimetry, etc. 2 Enthalpy Changes: Formation Reactions Δ H f ° Standard molar enthalpies of formation: enthalpies per mol of reaction Δ H f of a substance starting from the elements in their stable state at standard conditions (1 bar and 25°C)       -1 1 2 2 2 2 H g O g H O 285.8kJmol f H         0 -1 2 2 4 2C graphite 2H g C H g 52.26kJmol f H     0 22 H g H g 0 f H The enthalpy of formation of an element in its standard state at 25°C is zero. 3       11 H g Cl g HCl g    Hg   Cl g +   H--H H    Cl--Cl H   H--Cl H H             0,endothermic 0,endotherm 0,exothermic ic H- - H- H Cl- -Cl -Cl HH H H   // 4 Enthalpy is a function of state. For any given transformation: (initial) → (final) ΔH is independent of the path . We can combine any number of auxiliary reactions and their enthalpies to calculate the enthalpy of a reaction of interest.
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Lec-04-Chap06-4 9/9/2009 Standard Enthalpies of reaction Enthalpies of formation. Calorimetry, etc. 3 Enthalpy Changes in Chemical Reactions: Hess’s Law Because enthalpy is a function of state , we can combine any number of auxiliary reactions and their enthalpies to calculate the enthalpy of a reaction of interest.         9 3 6 2 2 2 2 C H g O g 3CO g 3H O ? H                                  0 -1 2 3 6 3 6 0 -1 2 2 2 01 1 2 2 2 2 2 3C graphite 3H g C H g C H g 103.85kJ mol C graphite O g CO g CO g 393.51kJ mol H g O g H O H O 285.83kJ mol f f f H H H       5 Enthalpy Changes in Chemical Reactions: Hess’s Law - continued                               0 -1 2 3 6 3 6 0 -1 2 2 2 1 2 2 2 2 2 3C graphite 3H g C H g C H g 103.85kJ mol C graphite O g CO g CO g 393.51kJ mol
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This note was uploaded on 01/02/2010 for the course CHE 132 taught by Professor Hanson during the Fall '08 term at SUNY Stony Brook.

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Lec-04-Chap06-4 - Lec-04-Chap06-4 Lec-04 Chemical...

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