JEE MAIN - Chemistry (2019 - 11th January Evening Slot - No. 13)
The reaction 2X $$ \to $$ B is a zeroth order reaction. If the initial concentration of X is 0.2 M, the half-life is 6 h. When the initial concentration of X is 0.5 M, the time required to reach its final concentration of 0.2 M will
be:
18.0 h
9.0 h
7.2 h
12.0 h
Explanation
For zero order reaction,
t1/2 = $${{{a_0}} \over {2k}}$$
$$ \Rightarrow $$ k = $${{{a_0}} \over {2{t_{1/2}}}}$$ = $${{0.2} \over {2 \times 6}}$$ = 1.67 $$ \times $$ 10-2 mol Lā1hā1
For zero order reaction,
A0 - At = kt
$$ \Rightarrow $$ 0.5 - 0.2 = 1.67 $$ \times $$ 10-2 t
$$ \Rightarrow $$ t = $${{0.3} \over {1.67 \times {{10}^{ - 2}}}}$$ = 18 h
t1/2 = $${{{a_0}} \over {2k}}$$
$$ \Rightarrow $$ k = $${{{a_0}} \over {2{t_{1/2}}}}$$ = $${{0.2} \over {2 \times 6}}$$ = 1.67 $$ \times $$ 10-2 mol Lā1hā1
For zero order reaction,
A0 - At = kt
$$ \Rightarrow $$ 0.5 - 0.2 = 1.67 $$ \times $$ 10-2 t
$$ \Rightarrow $$ t = $${{0.3} \over {1.67 \times {{10}^{ - 2}}}}$$ = 18 h
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