Question

A key step in balancing chemical equations is correctly identifying the formulas of the reactants and products. For example, consider the reaction between calcium oxide, CaO(s), and \(\mathrm{H}_{2} \mathrm{O}(l)\) to form aqueous calcium hydroxide. (a) Write a balanced chemical equation for this combination reaction, having correctly identified the product as \(\mathrm{Ca}(\mathrm{OH})_{2}(a q)\) . (b) Is it possible to balance the equation if you incorrectly identify the product as \(\mathrm{CaOH}(a q),\) and if so, what is the equation?

Short answer

The balanced chemical equation with the correct product, Ca(OH)₂(aq), is \(CaO(s) + 2H_2O(l) \rightarrow Ca(OH)_2(aq)\). It is not possible to balance the equation with the incorrect product, CaOH(aq), since it would create an imbalance in the number of H atoms.

Step-by-step solution

(a) Writing the balanced chemical equation with the correct product: Ca(OH)₂(aq)

To write a balanced chemical equation for this combination reaction, we first write the skeleton equation (unbalanced equation) using the given reactants and identified product: \(CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq)\) Now, we'll balance the equation by ensuring that there are the same number of atoms of each element on both sides. Our equation has 1 Ca, 1 O, and 2 H atoms on the left side: 1. Ca atoms: 1 on both sides. No change needed. 2. O atoms: 1 on both sides. No change needed. 3. H atoms: 2 on the right side, so we'll add a coefficient of 2 in front of H₂O: \(CaO(s) + 2H_2O(l) \rightarrow Ca(OH)_2(aq)\) Now, our balanced chemical equation for this reaction is: \(CaO(s) + 2H_2O(l) \rightarrow Ca(OH)_2(aq)\)

(b) Balancing the equation with an incorrect product: CaOH(aq)

First, let's write the skeleton equation using the incorrect product, CaOH(aq): \(CaO(s) + H_2O(l) \rightarrow CaOH(aq)\) Now, we will try to balance this equation as before: 1. Ca atoms: 1 on both sides. No change needed. 2. O atoms: 1 on both sides. No change needed. 3. H atoms: 1 on the right side, however, we need to have 2 H atoms on the left side. Here, we cannot balance H atoms by adding a coefficient since increasing the amount of H₂O would affect the balance of O atoms. It becomes clear that balancing the equation using the incorrect product is not possible. So, the answer is no, it is not possible to balance the equation using CaOH(aq) as the product.

Key concepts

Chemical Reaction

Understanding the intricate dance of atoms and molecules during a chemical reaction is key to grasping concepts in chemistry. A chemical reaction occurs when substances, known as reactants, transform into new substances called products. This transformation is the result of changes in the way atoms bond with each other.

During a chemical reaction, the type of atoms remains the same, but their arrangement and chemical bonds change. It can be illustrated in a form of a chemical equation, which is like a recipe for chemistry. The process could analogously be compared to rearranging Lego blocks into a new shape. No matter the reaction, whether it's a car rusting or baking soda reacting with vinegar, atoms are neither created nor destroyed; they're just rearranged.

To provide a clearer understanding, let's delve into an example of water forming rust, written as: \[4\text{Fe} + 3\text{O}_{2} \rightarrow 2\text{Fe}_{2}\text{O}_{3}\]. The equation indicates that four iron atoms react with three oxygen molecules to yield two molecules of iron(III) oxide. Simple yet powerful, the nuances of chemical equations unveil the core of what's happening in a beaker or, for that matter, within the stars.

Combination Reaction

In the diverse world of chemical reactions, a combination reaction is like a meet-cute in a romantic film where two separate entities 'combine' to form a single product. Simply put, it involves reactants joining forces to create a more complex molecule. A classic example is when metallic elements react with oxygen to form oxides. These reactions are fundamental to building more complex compounds from simpler ones.

Real-Life Example

Consider the reaction where calcium oxide and water unite to form calcium hydroxide: \[CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq)\]. In this scenario, our first step is always to identify reactants and products accurately. Calcium hydroxide, with its two hydroxide ions, is the product of water, a simple molecule, combining with calcium oxide, a basic oxide. It's analogous to two puzzle pieces coming together to complete the picture. Misidentification of the product, as shown in the alternative incorrect equation \[CaO(s) + H_2O(l) \rightarrow CaOH(aq)\], where calcium hydroxide is incorrectly noted as CaOH, results in an unbalanced reaction, the chemical equivalent of a puzzle that just won't fit.

Law of Conservation of Mass

At the heart of every balanced chemical equation lies the immutable law of conservation of mass, which states that mass in an isolated system is neither created nor destroyed by chemical reactions. Originating from Antoine Lavoisier in the late 18th century, this law indicates that the mass of the reactants must equal the mass of the products.

Application in Chemical Equations

When balancing chemical equations, we're essentially ensuring that mass is conserved following this law. In our previous example of forming calcium hydroxide, as we balance reactants and products, we satisfy the condition that the number and type of each atom on the left side (reactants) exactly matches those on the right side (products). It is crucial to bear in mind that while coefficients of molecules can change to balance the equation, the formulas of the substances involved cannot be altered. This underscores why incorrectly identifying a product, as seen in the incorrect equation involving CaOH, leads to an impossibility in obeying this conservation law. The balancing act in chemical equations is a testament to the enduring relevance of Lavoisier's legacy in modern chemistry.