The reaction between dilute hydrochloric acid and magnesium ribbon are fast at the beginning and gradually slows down thereafter. This observed gradual decrease in the of reaction is due to;
Increase in pressure above the reaction vessel brought about by the hydrogen gas being produced
Insolubility of the magnesium chloride being produced
Gradual decrease in the number of hydrogen ions during the reactions.
Endothermic reaction between magnesium ions and chloride ions
