Problem 16 - Chemistry: The Central Science

Question

(a) Determine the chemical formula of the product formed when the metallic element calcium combines with the nonmetallic element oxygen, \(\mathrm{O}_{2}\). Write the balanced chemical equation for the reaction. (b) What products form when a compound containing \(\mathrm{C}, \mathrm{H}\), and \(\mathrm{O}\) is completely combusted in air? Write a balanced chemical equation for the combustion of acetone, \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}(l)\), in air.

Step-by-Step Solution

Answer

The chemical formula for the product formed when calcium combines with oxygen is CaO. The balanced chemical equation for the reaction between calcium and oxygen is: \(2Ca + O_2 \rightarrow 2CaO\). When a compound containing carbon (C), hydrogen (H), and oxygen (O) is completely combusted in air, the combustion products are carbon dioxide (CO2) and water (H2O). The balanced chemical equation for the combustion of acetone (\(C_3H_6O\)) in air is: \(C_3H_6O(l) + \dfrac{5}{2}O_2(g) \rightarrow 3CO_2(g) + 3H_2O(g)\).

Step 1: (a) Determine the chemical formula for Ca and O2 reaction

To determine the chemical formula of the product formed when calcium (Ca) combines with oxygen (O2), we need to recall the general rule for the formation of ionic compounds: The charges of the ions in the compound must cancel each other out. Calcium (Ca) forms +2 ions, while oxygen (O) typically forms -2 ions. The chemical formula for the compound will have one calcium ion and one oxygen ion. Therefore, the chemical formula for the product is CaO.

Step 2: (a) Write the balanced chemical equation for the Ca and O2 reaction

To write the balanced chemical equation for the reaction between calcium (Ca) and oxygen (O2), we first write the reactants and products: Ca + O2 → CaO Now, we balance the chemical equation by ensuring the same number of atoms of each element are on both sides of the equation. 2Ca + O2 → 2CaO Thus, the balanced chemical equation for the reaction between calcium and oxygen is: 2Ca + O2 → 2CaO

Step 3: (b) Determine the products of complete combustion of a compound containing C, H, and O

When a compound containing carbon (C), hydrogen (H), and oxygen (O) is completely combusted in air, the combustion products are carbon dioxide (CO2) and water (H2O).

Step 4: (b) Write a balanced chemical equation for the combustion of acetone

The chemical formula of acetone is \(C_3H_6O\). To write a balanced chemical equation for the combustion of acetone in air, we start with the reactants (acetone and oxygen) and products (carbon dioxide and water): C3H6O(l) + O2(g) → CO2(g) + H2O(g) Now, we balance the chemical equation by ensuring the same number of each element's atoms on both sides of the equation. First, count the number of atoms for each element: - Carbon: 3 (in acetone) - Hydrogen: 6 (in acetone) - Oxygen: 1 (in acetone) + 2 (in oxygen) To balance the equation, we need: - Three molecules of CO2 for carbon atoms (3C in acetone → 3CO2); - Three molecules of H2O for hydrogen atoms (6H in acetone → 3H2O). The balanced chemical equation is: \(C_3H_6O(l) + \dfrac{5}{2}O_2(g) \rightarrow 3CO_2(g) + 3H_2O(g)\) So, the balanced chemical equation for the combustion of acetone in air is: \(C_3H_6O(l) + \dfrac{5}{2}O_2(g) \rightarrow 3CO_2(g) + 3H_2O(g)\)

Key Concepts

Chemical Equations

A chemical equation represents a chemical reaction, displaying both reactants and products. Think of it as a recipe, showing how ingredients (reactants) are transformed into a dish (products). Writing a chemical equation involves several steps:
First, identify the reactants and products. For example, when metallic calcium reacts with oxygen, the reactants are calcium (Ca) and oxygen (\(O_2\)). The product is calcium oxide (CaO). The equation starts by showing these substances in their chemical form:

• Reactants: Ca + \(O_2\)
• Product: CaO

However, this equation isn't balanced. A balanced chemical equation must have the same number of each type of atom on both sides. For calcium and oxygen:\[\text{2Ca} + \text{O}_2 \rightarrow \text{2CaO}\]This equation is now balanced, meaning there are two calcium atoms and two oxygen atoms on each side. This principle ensures mass conservation in reactions.
In every chemical reaction, the coefficients (numbers in front of molecules) indicate mole ratios, crucial for predicting how much of each substance is needed or produced.

Ionic Compounds

Ionic compounds are formed when metals and nonmetals chemically combine. Metals, like calcium (Ca), tend to lose electrons, forming positively charged ions. Nonmetals, such as oxygen (O), gain electrons, resulting in negatively charged ions. The compound stabilizes when the total positive charge equals the total negative charge.
An ionic bond is the attraction between these oppositely charged ions. For calcium oxide (CaO), the calcium ion (\(Ca^{2+}\)) and the oxide ion (\(O^{2-}\)) attract each other. Here's what typically happens:

• Calcium loses two electrons: \(\text{Ca} \rightarrow \text{Ca}^{2+} + 2e^-\)
• Oxygen gains two electrons: \(\text{O}_2 + 4e^- \rightarrow 2\text{O}^{2-}\)

The result is CaO, a neutral compound with balanced charges.
Ionic compounds generally have high melting points and are good conductors of electricity when dissolved in water, because the ions are free to move.

Combustion Reactions

Combustion reactions occur when a substance reacts swiftly with oxygen, releasing energy as heat and light. They generally involve a hydrocarbon (a molecule containing hydrogen and carbon) and oxygen (\(O_2\)). The products are typically carbon dioxide (\(CO_2\)) and water (\(H_2O\)).
For instance, during the combustion of acetone (\(C_3H_6O\)), the process can be broken down as follows:

• Start with the reactants: acetone and oxygen: \(\text{C}_3\text{H}_6\text{O} + \text{O}_2\)
• The main products after complete combustion are: \(CO_2\) and \(H_2O\)

Balancing this reaction typically requires adjustments in the coefficients. For acetone:\[\text{C}_3\text{H}_6\text{O}(l) + \frac{5}{2}\text{O}_2(g) \rightarrow 3\text{CO}_2(g) + 3\text{H}_2\text{O}(g)\]This equation illustrates the needed proportions to ensure that all carbon atoms form carbon dioxide and all hydrogen atoms convert into water.
These reactions are practical in everyday life, from burning fuels for cars to everyday fires, widely used for heating and cooking.