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NCERT Class XII Chemistry
Chapter - Chemical Kinetics
Questions with Solutions

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Question : 3
Total: 39
The decomposition of NH3 on platinum surface is zero order reaction. What are the rates of production of N2 and H2 if k=2.5×10–4 molL–1s–1 ?
Solution:  
For the reaction, 2NH3→N2+3H2
Rate=−
1
2
d [ NH3 ]
dt
=
d [ N2 ]
dt
=
1
3
d [ H2 ]
dt
‌‌‌‌‌...(1)
For zero order reaction
Rate = k‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌ ...(2)
From equation (1) and (2)
Rate=−
1
2
d [ NH3 ]
dt
=
d [ N2 ]
dt
=
1
3
d [ H2 ]
dt
=k‌‌‌‌‌‌...(3)
∴‌ Rate of production of N2=
d [ N2 ]
dt
=k
k=2.5×10−4 mol L−1 s−1
∴‌ Rate of production of N2=k=2.5×10−4 mol L−1 s−1
From equation (3)
Rate of production of H2=
d [ H2 ]
dt

=3k
=3×2.5×10−4 mol L−1 s−1
=7.5×10−4 mol L−1 s−1
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