When writing a chemical reaction you must satisfy these two laws of chemistry: 1. The law of conservation of mass: The mass of the reactants must equal the mass of the products. 2. The law of definite proportions: When making a certain chemical there is only one correct ratio of reactants. To make hydrogen chloride or any other chemical there is only one ratio of reactants that works so that all of the hydrogen and chlorine are used to make hydrogen chloride. Try several different ratios to see which ones form a complete reaction with nothing left over. What is the simplest ratio of hydrogen to chlorine for forming hydrogen chloride?