For the reaction below, which statement best describes what is happening with the sign of AGO CrP O4t6) 3 Na Cla g) - N agP O4la q) * CrClala glendothermic) The reaction is spontaneous at low temperature and non-spontaneous at high temperature. The reaction is non-spontaneous at all temperatures. The reaction is non-spontaneous at low temperature and spontaneous at high temperature. The reaction is spontaneous at all temperatures.
The chemical equation may be written as:
On the right side (products) one mole of
CrCl3→ Cr+3 + 3Cl- ( 4 mole ions)
and
Na3PO4→ 3Na+ + PO4-3 ions (4 mole ions) total moles on right side 8 moles
So, in this reaction number of moles from left to right increase hence ΔS0 is +ve and it is an endothermic reaction ΔH0 is +ve
Free energy decides spontaneity of a reaction
Mathematically,
Apply in Gibbs equation
Where,
G= Gibb's free energy
H= Change in enthalpy
T = Temperaature
S= Change in entropy
Since, ΔH is +ve and ΔSis +ve then ΔG become -ve at high temperatures.
Criteria for the spontaneity:
(i)
If G = 0, reaction is in equilibrium.
(ii) If G = -ive i.e G<0, reaction is spontaneous.
(iii) If G = +ive i.e G>0, reaction is non-spontaneous.
For endothemic reaction change in entropy always positive,
H = + ive value.
For exothermic
H = - ive value.
Entropy of any irreversible reaction is positive.
since this is endothermic reaction
H = + ive value.
so, if temperature is low,
H >T S
G is +ive( non- spontaneous)
At high temperature
H <T S
Therefore, G is -ive( spontaneous)
At lower temperature it will non spontaneous.
Hence, option A is inncorrect.
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