Consider the reaction NH4NO3(s)N2O(g)+2H2O(l) at 298 K. A) Is the forward reacti

Question

Consider the reaction NH4NO3(s)N2O(g)+2H2O(l) at 298 K.

A) Is the forward reaction endothermic or exothermic?

B) What is the value of G at 298 K? Express your answer to four significant figures and include the appropriate units.

C) What is the value of K at 298 K? Express your answer using two significant figures.

D) Does the reaction tend to occur spontaneously at temperatures above 298 K, below 298 K, both, or neither?

below 298 K            

at no temperature   

at all temperatures

above 298 K

Explanation / Answer

a)

NH4N03 ---> N20 + 2H20

we know that

dHo rxn = dHof products - dHof reactants

so

dHo rxn = dHof N20 + ( 2 x dHof H20) - dHof NH4N03

dHo rxn = ( 82.05) + ( 2 x -285.8) - (-365.6)

dHo rxn = -124 kJ

so

the forward reaction is exothermic

b)

now

dGo rxn = dGo products - dGo reactants

so

dGo rxn = dGo N20 + ( 2 x dGo H20) - dGo NH4N03

dGo rxn = 104.2 + ( 2 x -237.1) + 183.9

dGo rxn = -186.1 kJ

c)

now

dGo = -RTlnK

so

-186.1 x 1000 = -8.314 x 298 x ln K

K = 1.3 x 10^75

d)

now

dSo rxn = So products - So reactants

dSo rxn = ( So N20 + 2 x So H20) - So NH4N03

dSo rxn = 219.9 + ( 2 x 69.91) - 151.1

dSo rxn = 209 J/K

now

dGo = dHo - TdSo

As

dHO is -

and

dSo is +

dGo < 0 at all temperatures

so

the reaction is spontaneous at all temperatures

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