Diploma Food Technology
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