Problem 23 - Chemistry in 30 days

Question

If \(30 \mathrm{~mL}\) of \(\mathrm{H}_{2}\) and \(20 \mathrm{~mL}\) of \(\mathrm{O}_{2}\) react to form water. What is left at the end of the reaction? (a) \(10 \mathrm{~mL}\) of \(\mathrm{H}_{2}\) (b) \(5 \mathrm{~mL}\) of \(\mathrm{H}_{2}\) (c) \(10 \mathrm{~mL}\) of \(\mathrm{O}_{2}\) (d) \(5 \mathrm{~mL}\) of \(\mathrm{O}_{2}\)

Step-by-Step Solution

Answer

(d) 5 mL of \(\text{O}_2\)

Step 1: Write the Balanced Chemical Equation

The reaction of hydrogen gas with oxygen gas to form water can be represented by the chemical equation: \ \[ 2 ext{H}_2 + ext{O}_2 \rightarrow 2 ext{H}_2 ext{O} \] \ This equation shows that two volumes of hydrogen react with one volume of oxygen.

Step 2: Determine the Limiting Reactant

The volumes given for the reaction are 30 mL of \(\text{H}_2\) and 20 mL of \(\text{O}_2\). According to the stoichiometry of the reaction, 2 parts of hydrogen are needed for every 1 part of oxygen. Therefore, for 20 mL of \(\text{O}_2\) to fully react, we need: \ \[ 2 \times 20 \text{ mL} = 40 \text{ mL of } \text{H}_2 \]\However, there are only 30 mL of \(\text{H}_2\) available, which means \(\text{H}_2\) is the limiting reactant.

Step 3: Calculate Remaining Reactants

Since \(\text{H}_2\) is the limiting reactant, it will be completely consumed. From the stoichiometry, 30 mL of \(\text{H}_2\) will react with:\\[ \frac{1}{2} \times 30 \text{ mL} = 15 \text{ mL of } \text{O}_2 \] \Since you start with 20 mL of \(\text{O}_2\), after the reaction, \(20 \text{ mL} - 15 \text{ mL} = 5 \text{ mL of } \text{O}_2\) will be left.

Step 4: Conclusion from Calculations

From the calculations, after the entire reaction occurs, only \(5 \text{ mL of } \text{O}_2\) remains unreacted.

Key Concepts

Balanced Chemical Equation

In any chemical reaction, a balanced chemical equation is crucial. It dictates how substances transform from reactants into products. The chemical equation for the reaction between hydrogen and oxygen to form water is \[ 2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O} \].

* The coefficients in the equation represent the ratio of molecules involved in the reaction. Here, it shows that 2 volumes of hydrogen gas react with 1 volume of oxygen gas.

This ensures that both the number of atoms and charge are conserved on both sides of the equation. Balancing equations is essential in predicting the quantities of reactants needed or products formed.

Stoichiometry

Stoichiometry is the calculations of reactants and products in chemical reactions. It utilizes the balanced chemical equation to determine relationships.

* In our reaction, the stoichiometric coefficients are crucial for determining how much of each reactant is needed. From \( 2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O} \), the ratio is 2:1.

This means for every 2 volumes of hydrogen, 1 volume of oxygen is needed. Stoichiometry allows us to predict how much reactant will remain or be consumed in a reaction, which is key in identifying the limiting reactant.

Reactants and Products

In chemical reactions, reactants are substances used, and products are the substances formed. In our example, hydrogen and oxygen are reactants, while water is the product.

* Reactants are consumed during the reaction. Their ratios, as seen through stoichiometry, determine how the reaction proceeds.

Recognizing the difference is important for understanding any reaction. Products are derived from reactants according to the balanced chemical equation, which in this case is water, formed by combining hydrogen and oxygen.

Chemical Reaction

A chemical reaction involves the transformation of substances through breaking and forming chemical bonds. When hydrogen and oxygen react, they undergo a chemical change to form water.

* Chemical reactions follow specific paths dictated by the chemical equation.

In our case, the reaction can only continue until one of the reactants runs out. This is governed by the balanced chemical equation, reflecting how reactants combine to create new products under defined conditions. Understanding the nature of these reactions is crucial to comprehending how substances interact in the world.