Diploma Food Technology

Physical Chemistry

Lesson Plans

 

Lesson Plan 12

 

Reference: Think Quest

http://library.thinkquest.org/3659/structures/

                                                http://encarta.msn.com/encnet/refpages/refarticle.aspx?refid=761576933

 

 

 

Lesson 12

 Revision of         PV = nRT

 

Calculation of Molecular weight of vapors

And volumes of masses of a liquid.

 

 

Heats of Reactions

 

 

 

DH = Heats of Reaction at constant Pressure

Eg     C  +  O2  à  CO2       DH  = - 94.03 kcal

 

-ve Means heat leaves the reaction.

 

Eg.   HCl   +   NaOH  à  NaCl  +  H2O     DH  = - 13.7  kcal

 

DE = “Heats of Reaction” at constant volume

 

   DE  =  DH  -  PDV

                               

               

DE  =  DH  -  nRTDV

 

 

Heat of formation.

 

Heat need to make a molecule from it’s elements.

Assumes elements have zero heat of formation

 

2C  +  3H2  à C2H6    DH  =  - 23.4 kcal

 

Heat of formations determination

 

                Too measure directly as many molecules are to difficult to make in the laboratory

It is possible to calculate HR  indirectly from the heat of reactions involving other molecules with known heat of reactions.  This is because the heat of reaction for a given reaction is equal to the difference in the heat of formations of the reactants and the  products.

 

                                                                CH4    +   2O2    à    CO2   +   2 H2O     DH  = -  212.7 kcal

 

Heat of formations                               -17.9         0               - 94.0       2 x (- 68.3)

 

 

 

 

Enthalpy

 

Exothermic and endothermic reactions

Spontaneous reactions

Down-hill reactions and up-hill reactions

 

Spontaneous Endothermic reactions

 

Entropy