# Zero order kinetics

For a given reaction A→ B, the rate constant is 1.2 × 10$^{–2}$ M s$^{–1}$. What is the concentration of B after 20 min., if we start with 10 M of A. It is zero order kinetics.

When I try to solve the question, the equation would be

$$x_i - x_f = kt$$ $$10 M - x_f = kt = (1.2×10^{–2}M s^{–1})(20 min)(60 s/min)$$

So, $$x_f=10M - 14.4 M$$ I do not understand how it can be negative.

• Why am I getting negative votes ? – Icandoahandstand99 Jan 5 '17 at 15:05
• How did you get 14.4 ? – Shailesh Jan 5 '17 at 16:11
• @Shailesh I get it from kt = 1.2x10$^{-2}$ (20x60) – Icandoahandstand99 Jan 5 '17 at 16:59
• Your math checks out. B cannot be negative, and indeed since the reaction forms B, it has to be zero. What's the highest it could go? Hint: first solve an alternate problem where you want to calculate the time $t$ it takes for A to be completely depleted. What is the concentration of B at that time, and at all times thereafter? – Curt F. Jan 5 '17 at 17:11