Problem 18 - Chemistry The Central Science In Si Units

Question

(a) When a compound containing C, H, and O is completely combusted in air, what reactant besides the hydrocarbon is involved in the reaction? (b) What products form in this reaction? (c) What is the sum of the coefficients in the balanced chemical equation for the combustion of one mole of acetone, \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}(l),\) in air?

Step-by-Step Solution

Answer

(a) Oxygen gas (\(O_2\)); (b) \(\text{CO}_2\) and \(\text{H}_2\text{O}\); (c) Sum of coefficients is 11.

Step 1: Identify the Reactant Involved

In the combustion of a compound containing carbon (C), hydrogen (H), and oxygen (O), the reactant involved in addition to the hydrocarbon is oxygen gas (\(O_2\)) from the air. Combustion requires \(O_2\) to form combustion products.

Step 2: Determine the Products Formed

In complete combustion reactions of hydrocarbons containing C, H, and O, the products formed are carbon dioxide \(\text{CO}_2\) and water \(\text{H}_2\text{O}\). No other products are formed under complete combustion conditions.

Step 3: Write the Combustion Reaction for Acetone

Write a balanced chemical equation for the combustion of acetone (\(\text{C}_3\text{H}_6\text{O}\)).\[ \text{C}_3\text{H}_6\text{O}(l) + x\,\text{O}_2(g) \rightarrow y\,\text{CO}_2(g) + z\,\text{H}_2\text{O}(l) \]

Step 4: Balance the Chemical Equation

Balance the equation by adjusting the coefficients. Ensuring each element has the same number on both sides of the equation:\[ \text{C}_3\text{H}_6\text{O}(l) + 4\,\text{O}_2(g) \rightarrow 3\,\text{CO}_2(g) + 3\,\text{H}_2\text{O}(l) \]Carbon: 3 atoms on each side, Hydrogen: 6 atoms on each side, Oxygen: 9 on both sides (from 4\(O_2\) and \(\text{C}_3\text{H}_6\text{O}\)).

Step 5: Calculate the Sum of Coefficients

Add up the coefficients of the balanced equation:- \(\text{C}_3\text{H}_6\text{O}(l): 1\)- \(\text{O}_2(g): 4\)- \(\text{CO}_2(g): 3\)- \(\text{H}_2\text{O}(l): 3\)The sum is \(1 + 4 + 3 + 3 = 11\).

Key Concepts

Chemical Equation Balancing

Chemical equation balancing is a key concept in chemistry. When reacting substances undergo chemical changes, we represent these changes using chemical equations. These equations must be balanced, meaning the same number of each type of atom must appear on both sides of the equation. This is essential because it reflects the law of conservation of mass, which states that mass cannot be created or destroyed in a closed system.

Balancing involves adjusting the coefficients (numbers written before the substances in the equation) to ensure that each element has the same quantity on both sides. For example, in the combustion of acetone, we start by writing the unbalanced chemical equation:

• \( \text{C}_3\text{H}_6\text{O}(l) + x\,\text{O}_2(g) \rightarrow y\,\text{CO}_2(g) + z\,\text{H}_2\text{O}(l) \)

Here, we identify the number of carbon, hydrogen, and oxygen atoms, and adjust the coefficients to balance them. This ensures the final equation is balanced:

• \( \text{C}_3\text{H}_6\text{O}(l) + 4\,\text{O}_2(g) \rightarrow 3\,\text{CO}_2(g) + 3\,\text{H}_2\text{O}(l) \)

Hydrocarbon Combustion

Hydrocarbon combustion is a type of chemical reaction where a hydrocarbon reacts with oxygen gas, commonly from the air, to produce carbon dioxide and water. Hydrocarbons are compounds primarily composed of carbon (C) and hydrogen (H) atoms.

The complete combustion of hydrocarbons, such as acetone, follows a general pattern where all carbon atoms in the hydrocarbon form carbon dioxide, and all hydrogen atoms form water. This type of reaction is especially important in contexts like burning fuels where complete combustion is desired for maximum energy efficiency and minimal pollution.

In the combustion of acetone:

• The balanced reaction involves acetone reacting with 4 moles of oxygen gas to yield 3 moles of carbon dioxide and 3 moles of water.
• This can be represented as:\( \text{C}_3\text{H}_6\text{O}(l) + 4\,\text{O}_2(g) \rightarrow 3\,\text{CO}_2(g) + 3\,\text{H}_2\text{O}(l) \).

Oxygen in Combustion

Oxygen is crucial in the combustion process, acting as a reactant that helps facilitate the chemical reaction. In the context of hydrocarbon combustion, oxygen gas (\(O_2\)) interacts with hydrocarbons to break down chemical bonds in the hydrocarbons, releasing energy, and forming new chemical bonds in the products: carbon dioxide and water.

For complete combustion to occur, a sufficient amount of oxygen must be present. If not enough oxygen is available, incomplete combustion may result, producing carbon monoxide or carbon (soot) in addition to carbon dioxide and water.

Key points about oxygen in combustion:

• Oxygen gas (\(O_2\)) from the atmosphere is the primary source of oxygen for combustion reactions.
• In the balanced equation of acetone combustion, 4 moles of oxygen gas are required.\( \text{C}_3\text{H}_6\text{O}(l) + 4\,\text{O}_2(g) \rightarrow 3\,\text{CO}_2(g) + 3\,\text{H}_2\text{O}(l) \).
• Ensuring enough oxygen is available is vital for achieving complete combustion, making it a key factor in designing engines and other combustion-based applications.