The balanced chemical equation for the combustion of methane is:
CH4(g)+2O2(g) → CO2(g) + 2H2O(g)
Which of the following statements concerning this chemical equation is/are correct?
One gram of methane gas reacts with two grams of dioxygen
- gas, producing one gram of carbon dioxide gas and two grams of gaseous water.
One mole of methane gas reacts with two moles of dioxygen - gas, producing one mole of carbon dioxide gas and two moles of gaseous water.
One molecule of methane gas reacts with two molecules of - dioxygen gas, producing one molecule of carbon dioxide gas and two molecules of gaseous water.
Select one:
a. 2 and 3
b. I and 3
c. 1.2 and 3
d. 2 only
e. I only
The correct answer and explanation is :
The correct answer is:
a. 2 and 3
Explanation:
The balanced chemical equation for the combustion of methane is:
[
CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g)
]
This equation tells us that one molecule of methane reacts with two molecules of oxygen to produce one molecule of carbon dioxide and two molecules of water. It also applies on a mole basis: one mole of methane reacts with two moles of oxygen, yielding one mole of carbon dioxide and two moles of water.
Statement 1:
“One gram of methane gas reacts with two grams of dioxygen gas, producing one gram of carbon dioxide gas and two grams of gaseous water.”
This statement is incorrect because the mass relationships do not match the molecular weights. The molar masses are:
- Methane (CH₄) = 16 g/mol
- Oxygen (O₂) = 32 g/mol
- Carbon dioxide (CO₂) = 44 g/mol
- Water (H₂O) = 18 g/mol
Using mass calculations:
- 1 g of CH₄ corresponds to 1 g / 16 g/mol = 0.0625 moles
- From the equation, CH₄ reacts with 2 moles of O₂ per mole of CH₄, so oxygen required would be 0.125 moles of O₂. In grams, this is 0.125 × 32 = 4 g of O₂
- The products formed are 0.0625 moles of CO₂ (0.0625 × 44 = 2.75 g CO₂) and 0.125 moles of H₂O (0.125 × 18 = 2.25 g H₂O)
Clearly, 1 g CH₄ does not react with 2 g O₂. The mass ratios in the given statement are incorrect, so Statement 1 is false.
Statement 2:
“One mole of methane gas reacts with two moles of dioxygen gas, producing one mole of carbon dioxide gas and two moles of gaseous water.”
This follows directly from the balanced equation. Statement 2 is correct.
Statement 3:
“One molecule of methane gas reacts with two molecules of dioxygen gas, producing one molecule of carbon dioxide gas and two molecules of gaseous water.”
This also follows directly from the equation at the molecular level. Statement 3 is correct.
Since statements 2 and 3 are correct, the correct answer is option a (2 and 3).