Question

Using the laws of constant composition and the conservation of mass, complete the molecular picture of hydrogen molecules \((\bigcirc-\bigcirc)\) reacting with chlorine molecules \((\square-\square)\) to give hydrogen chloride \((\square-\bigcirc)\) molecules.

Short answer

Answer: The molecular representation is: Reactants: \(\bigcirc-\bigcirc + \square-\square\) Products: \(\square-\bigcirc + \square-\bigcirc\)

Step-by-step solution

1. Write down the balanced chemical equation

First, let's write down the balanced chemical equation for the reaction between hydrogen and chlorine molecules to form hydrogen chloride molecules. The reaction can be represented as: H₂(g) + Cl₂(g) -> 2HCl(g)

2. Apply the laws of constant composition and the conservation of mass

The balanced chemical equation shows that 1 mole of hydrogen reacts with 1 mole of chlorine to produce 2 moles of hydrogen chloride. During the reaction, the mass of the reactants and products remains constant, and the ratio of the masses of the elements in the reactants and products is the same. According to the conservation of mass, the total mass of the reactants must equal the total mass of the products. Since there is 1 mole of hydrogen and 1 mole of chlorine reacting, the mass of the reactants is: mass_H₂ + mass_Cl₂ = mass_reactants On the other hand, the mass of the products is equal to 2 moles of hydrogen chloride: 2 x mass_HCl = mass_products By the laws of constant composition: mass_reactants = mass_products

3. Draw the molecular picture

To complete the molecular picture, we need to represent the hydrogen molecules as \(\bigcirc-\bigcirc\), chlorine molecules as \(\square-\square\), and hydrogen chloride molecules as \(\square-\bigcirc\). Based on the balanced chemical equation, we can draw the following molecular picture: Reactants: \(\bigcirc-\bigcirc + \square-\square\) Products: \(\square-\bigcirc + \square-\bigcirc\) The reactants and products show that 1 hydrogen molecule and 1 chlorine molecule react to form 2 hydrogen chloride molecules while conserving mass and maintaining constant composition.

Key concepts

Laws of Constant Composition

The laws of constant composition, also known as the law of definite proportions, is a foundational principle in chemistry. It states that a chemical compound will always contain the same elements in the same proportion by mass, regardless of the sample size or the source of the compound. For example, water ((H_2O)) will always consist of hydrogen and oxygen in a mass ratio of approximately 1:8.

Thanks to this law, chemists can confidently work with chemical formulas and predict the outcomes of chemical reactions. When we express a reaction like the formation of hydrogen chloride ((HCl)), we know that every molecule formed will contain one hydrogen atom bonded to one chlorine atom. The predictable composition is crucial for understanding both the reactants and the products in a chemical reaction.

Conservation of Mass

The conservation of mass is a principle stating that in a closed system, mass cannot be created or destroyed by chemical reactions or physical transformations. This law, attributed to Antoine Lavoisier, is also known as the law of mass conservation. According to this principle, the mass of the reactants in a chemical reaction must equal the mass of the products.

When applying this to a chemical equation, like the reaction between hydrogen ((H_2)) and chlorine ((Cl_2)) to form hydrogen chloride ((2HCl)), we ensure that the number of atoms for each element is equal on both sides of the equation. The balanced equation provides a visual confirmation of the conservation of mass, as it shows that one molecule of hydrogen and one molecule of chlorine yield two molecules of hydrogen chloride, keeping the total mass the same before and after the reaction.

For further clarity, let's use an analogy. Imagine you have two loaves of bread (reactants) and you cut them into slices to make sandwiches (products). The number of slices (mass products) you end up with will be the same as the number of loaves you started with (mass reactants), illustrating that the mass remains consistent before and after the preparation, akin to a chemical reaction.

Balanced Chemical Equation

A balanced chemical equation is a representation of a chemical reaction with an equal number of atoms for each element on both sides of the equation. This balance is necessary to comply with the law of conservation of mass. In the reaction between hydrogen and chlorine, the balanced equation is: (H_2) + (Cl_2) → 2(HCl). This tells us that two atoms of hydrogen combine with two atoms of chlorine to form two molecules of hydrogen chloride.

In balancing chemical equations, we adjust the coefficients—the numbers placed before the compounds—to ensure there are equal numbers of each type of atom on both sides. These coefficients reflect the stoichiometry of the reaction, which is the quantitative relationship between reactants and products. It's much like a recipe where balancing ingredients is crucial to the outcome; too much or too little of one component will not yield the intended result. The balanced equation guides us in mixing the correct amounts of reactants to achieve the desired products, while respecting the conservation of mass and the laws of constant composition.