ABSTRACT
During a chemical reaction, the concentration of reactants decreases, and the concentration of products increases. The reaction velocity v is defined as the change in concentration of the reactants or products with time. The velocity of a reaction is always positive. For the definition of the reaction velocity in terms of the decrease of reactant concentration therefore need a negative sign to convert it into a positive value. The reaction velocity, on the other hand, must be identical independent of which change in concentration use as a reference. Bromine and hydrogen react in a multi-step radical reaction. First, Br2 decomposes into two bromine radicals: The radicals generated in this starting reaction can then react with molecular hydrogen producing hydrogen radicals. These hydrogen radicals also react with Br2 to give HBr leading to regeneration of a bromine radical, and keeping the chain-reaction going.
