AP EAPCET 07-Jul-2022 Shift 2 Paper

For the zero order reaction, A→3B the half-life is given by the formula t1∕2=A0∕2k where, A0 is the initial concentration and k is the rate constant.
After 15 s the concentration of A(0.1‌mol‌L−1) is reduced to its half value (0.05‌mol‌L−1),
So,t1∕2=15 s
k=01∕2×15=0.0033‌mol‌L−1‌ s−1
For zero order reaction after time ' t ' the concentration of reactant A is given by formula [A]=[A0]−kt
After t=20 s
[A]=0.1‌mol‌L−1−0.0033‌mol‌L−1‌ s−1×20 s
=0.033‌mol‌L−1
This implies that (0.1−0.033)=0.067 moles of reactant A are converted to product B.
Since, 1 mole of A gives 3 moles of B, so 0.067 moles of reactant A will give (0.066×3)=0.198 moles of B, i.e. 1.98×10−1 moles.