Question

A red signal flare for use on railroads is made by mixing strontium nitrate, carbon, and sulfur in the proportions as shown by the equation \(2 \mathrm{Sr}\left(\mathrm{NO}_{3}\right)_{2}+3 \mathrm{C}+2 \mathrm{~S} \rightarrow\) Complete and balance the equation (no atmospheric oxygen is necessary).

Short answer

The balanced chemical equation for the formation of a red signal flare using strontium nitrate, carbon, and sulfur is: \[2 Sr(NO_3)_2 + 3 C + 2 S \rightarrow 1 SrCO_3 + 1 SrS + 2 N_2 + 2 CO\]

Step-by-step solution

Write down the incomplete equation

The given incomplete equation is: \[2 Sr(NO_3)_2 + 3 C + 2 S \rightarrow (?)\] We need to determine the products and then balance the equation.

Identify the product formed

In a red signal flare, the main product formed after the combustion of strontium nitrate, carbon, and sulfur is strontium carbonate (SrCO_3) and strontium sulfide (SrS) alongside the formation of nitrogen gas (N_2) and carbon monoxide (CO). So our incomplete equation becomes: \[2 Sr(NO_3)_2 + 3 C + 2 S \rightarrow (?) SrCO_3 + (?) SrS + (?) N_2 + (?) CO\]

Balance the equation

Now we need to balance the equation by adjusting the coefficients of the reactants and products: Let's balance the strontium (Sr) atoms first: 2 Sr atoms on the left side, so we need 2 Sr atoms on the right side. Adjust the coefficients of SrCO_3 and SrS: \[2 Sr(NO_3)_2 + 3 C + 2 S \rightarrow 1 SrCO_3 + 1 SrS + (?) N_2 + (?) CO\] Next, balance the nitrogen (N) atoms: 4 N atoms on the left side (2 Sr(NO_3)_2), so we need 4 N atoms on the right side. Adjust the coefficient of N_2: \[2 Sr(NO_3)_2 + 3 C + 2 S \rightarrow 1 SrCO_3 + 1 SrS + 2 N_2 + (?) CO\] Now balance the carbon (C) atoms: 3 C atoms on the left side, so we need 3 C atoms on the right side. Since SrCO_3 has 1 C atom, adjust the coefficient of CO: \[2 Sr(NO_3)_2 + 3 C + 2 S \rightarrow 1 SrCO_3 + 1 SrS + 2 N_2 + 2 CO\] Finally, balance the sulfur (S) atoms: 2 S atoms on the left side, and there are already 2 S atoms on the right side in the SrS product. Thus, our equation is now balanced: \[2 Sr(NO_3)_2 + 3 C + 2 S \rightarrow 1 SrCO_3 + 1 SrS + 2 N_2 + 2 CO\]

Key concepts

Chemical Reaction

Understanding a chemical reaction is crucial as it forms the basis of the changes we see in chemistry. A chemical reaction involves the transformation of one or more substances, known as reactants, into new substances called products. This transformation occurs through the breaking and forming of chemical bonds. Chemical reactions can release or absorb energy, and they are represented by chemical equations that show the reactants and products along with their respective amounts.

In the context of the red signal flare used on railroads, the chemical reaction involves strontium nitrate, carbon, and sulfur as reactants. These substances undergo a chemical transformation when ignited, resulting in different products necessary for the red flare's visual effect. The ability to represent this chemical change through a balanced chemical equation is vital for understanding the amounts of each substance involved and the nature of the chemical reaction.

Stoichiometry

Stoichiometry is a section of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. It allows chemists to calculate the amount of reactants required to produce a certain amount of product, or vice versa. The stoichiometric coefficients in a balanced chemical equation indicate the ratio of moles of each substance involved in the reaction. These coefficients are essential for ensuring that the law of conservation of mass is upheld, meaning that the mass of the reactants equals the mass of the products.

In the exercise, balancing the stoichiometry of the red signal flare equation requires adjusting coefficients to ensure that the number of atoms of each element is the same on both sides of the equation. This step is essential for students to grasp because it not only enhances their problem-solving skills but also provides insight into how much of each substance is needed to create the flare, thus connecting mathematics to real-world chemical processes.

Red Signal Flare Composition

The composition of a red signal flare is specifically designed to produce a bright red light, often used as a distress signal or for illumination. The composition includes strontium nitrate, which imparts the red color to the flame when burned. Carbon and sulfur serve as fuel in the absence of atmospheric oxygen, aiding in the combustion process.

Understanding the composition is critical for ensuring the flare's effectiveness and safety. It's also an excellent example of how chemical principles apply to everyday items. By studying the chemical components and how they react, students gain insight into the practical aspects of chemistry and how it can be harnessed to serve specific functions, such as signaling or illumination in safety applications.

Combustion Products

Combustion products refer to the substances formed as a result of a combustion reaction, which is a type of chemical reaction where a fuel burns in the presence of an oxidizer to produce heat and light. In many cases, the oxidizer is atmospheric oxygen, but in the case of a red signal flare, the oxygen needed for the reaction is provided by the strontium nitrate. The combustion of the flare's composition does not rely on external oxygen sources, making it functional in environments where oxygen may be scarce.

The main combustion products of the red signal flare include strontium carbonate (SrCO₃), strontium sulfide (SrS), nitrogen gas (N₂), and carbon monoxide (CO). Each of these products plays a role in the overall reaction. For example, the formation of N₂ helps to neutralize the nitrogen from the strontium nitrate, and CO is a common product of incomplete combustion. The knowledge of these products is essential for anyone studying the science behind pyrotechnics, and it also emphasizes the importance of safety and environmental considerations when dealing with combustion reactions.