Why are chemical reactions often carried out using solutions? the heterogenous nature of solutions prevents the reactants from freely mixing. the amount of each reactant can be controlled by adjusting the volume of each solution that is used. even very small amounts of reactants can be combined by using dilute solutions. a color change will always occur when a reaction is conducted in solution. the molecules or ions in a solution can freely intermingle. the solvent must always be water, so it is impossible for a fire to start.