A substance decomposes on a metal surface by a zero order reaction. Its concentration falls from $0.80 mol L^{- 1}$ to $0.50 mol L^{- 1}$ in $30 min$ . Calculate the half-life (in minutes, one decimal) for the initial concentration of $0.80 mol L^{- 1}$ .

Numerical answer type, answer in min, tolerance 0.2.

Answer: 40 min

For zero order the rate is constant:

k = (0.80 - 0.50) /30 = 0.010 mol L^{- 1} mi n^{- 1}

. Then

t_{1/2} = [A]_{0} / (2 k) = 0.80/ (2 \times 0.010) = 40.0 min