In: Chemistry
C: CaCO3 (s) ----> CaO (s) + CO2 (g) delta H= +178
kJ/mol
D: PCl3 (g) + Cl2 (g) -----> PCl5 (g) delta H= - 88 kJ/mol
Classify these changes as either LEFTWARD SHIFT, RIGTHWARD SHIFT,
or NO SHIFT
System C increase temperature
System C decrease temperature
System D increase temperature
System D decrease temperature
since ?H for CaCO3 (s)< ----> CaO (s) + CO2 (g) is
positive(endothermic) so this reaction can be written in this
way...
CaCO3 (s) + Heat <-----> CaO (s) + CO2 (g) ..(Treat Heat as a
reagent)
if now you increase the temperature i.e. Heat is supplied to the
system then according to Le Chateller's principle equilibrium will
shift to that side that absorbs heat i.e. in forward direction or
rightward shift ...
similalrly if temperature is decreased equilibrium shifts to
backward direction or leftward shift ...
for system D ?H is negative (exothermic) ...so this
reaction can be written in this way :
PCl3 (g) + Cl2 (g) <----> PCl5 (g) + Heat
if temperature is increased then equilibrium will shift in that
direction which absorbs heat i.e. in backward direction or leftward
shift...
and decreasing temperature will shift the equilibrium to
right..
...................
And
Assume that these are meant to be equilibria.
in which case, C is intended to be a shift to the left. However,
you might point out to teacher that as entropy is negative (inc in
the no moles of gas) then increasing temp would tend to oppose the
positive value of the enthalpy change, so that the free energy
(delta G) would become increasingly negative. Since no information
is given on the temperature of this rxn, then it is not possible to
say.
In D, there are 2 moles on the left an d one on the right, entropy is positive, the term -(TdeltaS) becomes more negative as temp increases, in this case, teh rxn is favorable at all temperatures. If it is at equilibrium, an inc in temp would certainly shift the balance in the endothermic direction, to the left.