How do the rates of the forward and reverse reactions change throughout a reaction?

The rates of the forward and reverse reaction depends on the temperature on which the reaction will proceed, either endothermic of exothermic. it also depends of the concentration of the reactants and products. if the reaction is exothermic, so if the reaction temperature is increased then it will favor the forward reaction, then if the reaction is lowered then it will favor the reverse reaction

The mass has escaped into a gas which you can not see so the law stays true.