NCERT Class XII Chapter
Nuclei
Questions With Solutions
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Question : 15
Total: 31
The Q value of a nuclear reaction A + b → C + d is defined by Q = [ m A + m b – m c – m d ] c 2
(i)
H +
H
H +
H
(ii)
C +
C
N e +
H e
Atomic masses are given to be
m(
H ) (
H ) (
H )
m(
C ) (
N e )
(i)
(ii)
Atomic masses are given to be
m
m
Solution:
(i) Let us find the Q value in given first equation
H +
H
H +
H
Q =[ m (
H ) + m (
H ) − 2 m (
H ) ] c 2
= [1.007825 + 3.016049 – 2 × 2.014102] × (931 MeV)
Q = [4.023874 – 4.028204] 931.5 MeV = – 4.033 MeV
Negative Q value shows that reaction is endothermic.
(ii) Q value in the given second equation
C +
C
N e +
H e
Q =[ 2 m (
C ) − m (
N e ) − m (
H e ) ] c 2
Q = [2 × 12.0000 – 19.992439 – 4.002603] × 931.5 MeV
Q = 0.004958 × 931.5 MeV = 4.618 MeV
Positive Q shows that the reaction is exothermic.
Q =
= [1.007825 + 3.016049 – 2 × 2.014102] × (931 MeV)
Q = [4.023874 – 4.028204] 931.5 MeV = – 4.033 MeV
Negative Q value shows that reaction is endothermic.
(ii) Q value in the given second equation
Q =
Q = [2 × 12.0000 – 19.992439 – 4.002603] × 931.5 MeV
Q = 0.004958 × 931.5 MeV = 4.618 MeV
Positive Q shows that the reaction is exothermic.
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