Consider this reaction:
2H3PO4(aq)→ P2O5(aq)+ 3H2O

At a certain temperature it obeys this rate law. rate
rate= (46.6M^-1. s^-1) [H3PO4]^2

Suppose a vessel contains H3PO4 at a concentration of 0.660M. Calculate how long it takes for the concentration of H3PO$ to decrease to 20% to its natural value. You may assume no other reaction is important. Round your answer to significant digits.

  0.0345 sec

Explanation:

Rate law says that rate of a reaction is directly proportional to the concentration of the reactants each raised to a stoichiometric coefficient determined experimentally called as order.

k= rate constant =

Expression for rate law for first order kinetics is given by:

where,

k = rate constant

t = age of sample

a = let initial amount of the reactant

a - x = amount left after decay process  

for completion of 20 % of reaction

The time taken for the concentration of to decrease to 20% to its natural value is 0.0345 sec