Question

Write a balanced chemical equation for the reaction of solid strontium with iodine gas.

Short answer

The balanced chemical equation is: \(Sr(s) + I2(g) \rightarrow SrI2(s)\).

Step-by-step solution

Identify the Reactants

First, we need to identify the chemical formulas of the reactants. Strontium is a chemical element with the symbol Sr and iodine gas consists of I2 molecules. So, the reactants are solid strontium (Sr) and iodine gas (I2).

Write the Unbalanced Equation

Next, write the unbalanced chemical equation by placing the reactants on the left side and the expected product on the right side. The product of the reaction between a metal and a non-metal is an ionic compound, so the product here will be strontium iodide (SrI2). The unbalanced equation is: \(Sr(s) + I2(g) \rightarrow SrI2(s)\).

Balance the Equation

Finally, balance the chemical equation. Strontium, Sr, has a valency of +2, and iodine, I, has a valency of -1. For the ionic compound strontium iodide, we need two iodine atoms for every strontium atom to balance the charges. Also, iodine is diatomic in nature, meaning it exists as I2 in gaseous form. This leads to the balanced equation: \(Sr(s) + I2(g) \rightarrow SrI2(s)\). Since there is one Sr atom on both sides and 2 I atoms on both sides, the equation is balanced as written.

Key concepts

Chemical Reaction

A chemical reaction is the process where reactants transform into products through the breaking and forming of chemical bonds. Each reaction is governed by certain laws, one of which is the law of conservation of mass. This law states that mass is neither created nor destroyed in a chemical reaction. Therefore, the total mass of reactants must equal the total mass of products.

For example, when solid strontium reacts with iodine gas, they form a new substance, strontium iodide. This transformation is indicative of a chemical reaction occurring. It involves a metal (strontium) reacting with a non-metal (iodine), typically to form an ionic compound. Observing the changes and characterizing the reaction helps chemists understand and predict the behaviors of substances in various conditions.

Stoichiometry

Stoichiometry is essentially the 'mathematics of chemistry.' It deals with the quantitative relationships between the substances as they participate in chemical reactions. The principles of stoichiometry are used to ensure that the Law of Conservation of Mass is respected in the balanced chemical equations.

To apply stoichiometry, as first seen with the reaction of strontium and iodine, we start with the unbalanced equation and adjust coefficients to reflect the mass balance. Initially, Sr and I₂ might not have the same number of atoms on both sides, which is a common situation in unbalanced equations. Stoichiometry allows for determining the correct amount of reactants needed to produce desired quantities of products, as well as predicting the outcomes of reactions.

Valency

Valency is an integral part of understanding how elements combine during chemical reactions. It is defined as the combining power of an element, or the number of hydrogen atoms that can combine with or displace to form a compound. In the context of ionic compounds, it reflects the number of electrons an atom can lose, gain, or share to become stable.

Understanding Valency in Ionic Compounds

For ionic compounds, the valency of an element is crucial for determining the formula. The metal strontium (Sr) has a valency of +2, meaning it can donate two electrons. Iodine (I), on the other hand, has a valency of -1 and can accept one electron.

To achieve electrical neutrality, the charges must balance. That is why one Sr atom combines with two I atoms, leading to the formation of SrI₂. This valency-driven pairing is what makes stoichiometry possible and allows us to write the balanced chemical equation for the reaction between strontium and iodine.