Question

Iron and sulfur react to produce iron sulfide and heat energy. An experiment shows that the mass of iron and sulfur is equal to the mass of the iron sulfide. In theory, should the products weigh slightly more or slightly less than the reactants?

Short answer

The products should weigh the same as the reactants.

Step-by-step solution

Understand the Law of Conservation of Mass

The Law of Conservation of Mass states that in a closed system, the mass of the reactants equals the mass of the products. This principle is fundamental in chemistry and implies that mass can neither be created nor destroyed in a chemical reaction.

Analyze the Reaction

The reaction described involves iron (Fe) and sulfur (S) combining to form iron sulfide (FeS). The chemical equation can be written as: \( \text{Fe} + \text{S} \rightarrow \text{FeS} \). This is a combination reaction where two elements form a compound.

Apply the Law of Conservation of Mass

According to the Law of Conservation of Mass, the total mass of reactants (iron and sulfur) must equal the total mass of products (iron sulfide) because no atoms are lost in the process; they are simply rearranged. Thus, the mass of iron sulfide should equal the combined mass of the iron and sulfur used.

Theoretical Expectation

Theoretically, in a perfectly closed system with no external factors affecting the reaction, the mass of the products should be exactly equal to the mass of the reactants. There should be no gain or loss of mass.

Key concepts

chemical reactions

Chemical reactions involve the transformation of one or more substances into different substances, known as products.
This process alters the chemical composition and properties of the initial substances. In the exercise provided, iron (Fe) reacts with sulfur (S) to form iron sulfide (FeS). This specific reaction type is called a combination reaction, where two reactants combine to form a single product.

During a chemical reaction:

• The bonds between atoms in the reactants are broken and new bonds are formed in the products.
• The chemical equation for a reaction must be balanced to respect the Law of Conservation of Mass.

Chemical reactions can be influenced by various factors, such as temperature, pressure, and catalysts. However, no matter the conditions, the total number of atoms remains unchanged, although they are rearranged into new configurations. This rearranging of atoms and bonds is what forms the basis for the different physical properties and chemical characteristics seen in the products compared to the reactants.

mass balance

Mass balance is a crucial concept in chemistry and is deeply linked to the Law of Conservation of Mass. Essentially, mass balance refers to ensuring that the total mass of the reactants in a chemical reaction equals the total mass of the products. This principle can be explained through the reaction of iron and sulfur forming iron sulfide.

To fully understand mass balance, consider:

• Each atom that enters a reaction is accounted for in the products, implying no loss or gain of atoms.
• Accurate measurements in experiments are essential to confirm that mass remains consistent before and after a reaction.

Practically, when conducting experiments, chemists must consider potential factors that can affect mass measurements, such as measurement precision errors, all of which can slightly skew observed values. Nevertheless, the ideal outcome is that all atoms and thus all mass are conserved through careful balancing of the chemical equation.

closed system reactions

A closed system in chemistry is critical for observing true chemical dynamics without interference from external factors. In a closed system, all reactants and products are contained within the system, and no matter—including mass or energy—can enter or leave the system. This makes it an ideal setup for observing the Law of Conservation of Mass in action.

In a closed system:

• The environment does not contribute or remove any mass; thus, what's in it before the reaction must account for what is present afterward.
• All changes occur internally, and the mass of products can be directly traced back to the reactants.

While perfect closed systems are theoretical in nature, laboratory setups strive to recreate these conditions to study reactions by controlling variables such as temperature, pressure, and the containment of substances. By doing this, they aim to see the chemical principles at play in their most pure form, uninfluenced by external alterations.