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Difficulty: MediumChemical Reactions and Compounds

In an industrial chemical synthesis process, methane gas (CH4\text{CH}_4) reacts with high-temperature steam (H2O\text{H}_2\text{O}) to yield carbon monoxide (CO\text{CO}) and hydrogen gas (H2\text{H}_2) according to the following chemical equation:

CH4+H2O→CO+?‾H2\text{CH}_4 + \text{H}_2\text{O} \rightarrow \text{CO} + \underline{\quad ? \quad}\text{H}_2

What numerical coefficient must be placed in front of H2\text{H}_2 to balance the equation?

  1. A
    2
  2. B
    6
  3. 3Answer
  4. D
    4

Answer

The numerical coefficient that balances the equation is 3.
The reactant side has a total of 6 hydrogen atoms: 4 from methane (CH4\text{CH}_4) and 2 from steam (H2O\text{H}_2\text{O}). Since molecular hydrogen gas is diatomic (H2\text{H}_2), a coefficient of 3 provides 3×2=63 \times 2 = 6 hydrogen atoms, successfully satisfying the Law of Conservation of Mass while leaving carbon and oxygen balanced at 1 atom each on both sides.

Step-by-Step Solution

1
Tally the number of each type of atom on the reactant side of the equation.
Reactants: 1 Carbon atom (from CH4\text{CH}_4), 6 Hydrogen atoms (4 from CH4\text{CH}_4 plus 2 from H2O\text{H}_2\text{O}), and 1 Oxygen atom (from H2O\text{H}_2\text{O}).
According to the Law of Conservation of Mass, atoms cannot be created or destroyed, so total reactant atoms must equal total product atoms.
2
Tally the fixed atoms on the product side.
Products: 1 Carbon atom (in CO\text{CO}) and 1 Oxygen atom (in CO\text{CO}). Carbon and oxygen are already balanced (1 of each on both sides).
Identifies which elements are already balanced so attention can be directed to the unbalanced element.
3
Determine the required coefficient for diatomic hydrogen (H2\text{H}_2) to balance hydrogen.
To supply 6 hydrogen atoms using diatomic H2\text{H}_2 molecules: 6÷2=36 \div 2 = 3.
Multiplying the coefficient 3 by the subscript 2 yields 6 hydrogen atoms, balancing the equation.

Key Concept

Balancing Chemical Equations and Conservation of Mass
Estimated Time:1m 0s
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Topics

Chemical Reactions and Compounds

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