Problem 66 - Introductory Chemistry Atoms First

Question

Write the balanced chemical equation for the reaction that goes with the equilibrium constant \(K_{\mathrm{eq}}=\frac{\left[\mathrm{H}_{2} \mathrm{O}\right]^{2} \times\left[\mathrm{Cl}_{2}\right]^{2}}{[\mathrm{HCl}]^{4} \times\left[\mathrm{O}_{2}\right]}\)

Step-by-Step Solution

Answer

The balanced chemical equation for the reaction that goes with the given equilibrium constant is \[\ce{2HCl + O2 -> 2H2O + Cl2}. \]

Step 1: Write the unbalanced chemical equation

For this step, simply list down the reactants and products based on the equilibrium constant expression. Since the expression has HCl and O2 in the denominator, these two substances are likely to be the reactants. Meanwhile, H2O and Cl2, both in the numerator, are the products. The equation for now would look like: \[ \ce{HCl + O2 -> H2O + Cl2} \]

Step 2: Balance the equation

Now we will balance the equation by finding the appropriate stoichiometric coefficients for each substance in the equation. It's often easier to begin with a certain atom and proceed to balance others. Start with the oxygen atoms; there are 2 atoms in O2 and only 1 atom in H2O. So, we need 2 moles of H2O for every mole of O2 in the reaction: \[ \ce{HCl + O2 -> 2H2O + Cl2} \] Now, we'll balance the hydrogen atoms. Since there are 2 hydrogen atoms on each side, we need 2 moles of HCl for every mole of O2 in the reaction: \[ \ce{2HCl + O2 -> 2H2O + Cl2} \] Lastly, we need to balance the chlorine atoms. There are 2 chlorine atoms in both reactant 2HCl and product Cl2, so the equation is now balanced: \[ \ce{2HCl + O2 -> 2H2O + Cl2} \] The balanced chemical equation for the reaction that goes with the given equilibrium constant is \[ \ce{2HCl + O2 -> 2H2O + Cl2}. \]

Key Concepts

Chemical Equilibrium

Understanding chemical equilibrium is essential to grasp the dynamic nature of chemical reactions. It refers to a condition in which the concentrations of reactants and products in a closed system remain constant over time. This does not mean the reactants stop transforming into products or vice versa. Instead, the rate at which reactants convert to products is equal to the rate at which products convert back to reactants.

Using the equilibrium constant (\(K_{\text{eq}}\)), expressed in the given equation, helps us understand the ratio of product concentrations to reactant concentrations, each raised to the power of their stoichiometric coefficients in the balanced chemical equation. This constant is crucial for predicting the direction of the reaction under varying conditions and for calculating the concentrations of different components of the reaction at equilibrium.

To apply this concept to the exercise, the value of the equilibrium constant given as \(K_{\text{eq}}=\frac{[\mathrm{H}_{2} \mathrm{O}]^{2}\times[\mathrm{Cl}_{2}]^{2}}{[\mathrm{HCl}]^{4}\times[\mathrm{O}_{2}]}\) tells us that the reaction is at equilibrium when the squared concentrations of water and chlorine gas are proportional to the fourth power of the HCl concentration and the first power of the oxygen concentration.

Stoichiometry

Stoichiometry is the study of the quantitative aspects of chemical reactions. It involves the calculation of reactants and products in chemical reactions and is founded on the law of conservation of mass. The stoichiometric coefficients in a balanced chemical equation represent the ratios in which reactants combine and products form.

In practice, stoichiometry allows us to predict the amount of product that will form in a reaction from a given amount of reactant, or conversely, the amount of reactant needed to produce a desired amount of product. It's an essential tool for scientists in predicting the outcomes of reactions and is vital for industries that rely on chemical reactions for production.

When improving textbook exercises, one could incorporate examples that cover a variety of stoichiometric conversions, such as moles to grams, moles to liters of a gas at standard temperature and pressure, and percentage yield calculations to provide a more comprehensive understanding of stoichiometry.

Reaction Balancing

Balancing a chemical equation is critical because it shows the ratio in which chemicals react. It obeys the law of conservation of mass, which states that matter cannot be created or destroyed in a simple chemical reaction. Therefore, the number of atoms for each element must be the same on both sides of the equation.

When balancing a chemical equation, such as the one from the exercise, \(\ce{HCl + O2 -> H2O + Cl2}\), we look for the least common multiple for each atom on both the reactant and product sides. It's important to remember to balance elements that appear in only one reactant and one product first, progressing to those that are more complex. Always check your work to ensure that each side of the equation has the same number of atoms for each element.

An effective way to improve textbook exercises on reaction balancing is to include step-by-step examples that explain the thought process behind adding stoichiometric coefficients, as well as providing exercises with varying levels of complexity to cater to all learning levels. Additionally, practice problems could be complemented with visual aids that depict the conservation of atoms.