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Difficulty: EasyChemical Reactions and Compounds

Fill in the blank with the correct integer coefficient needed to balance the chemical equation.

Answer:In the complete combustion of methane, one molecule of methane reacts with oxygen to form carbon dioxide and water: CH4+2O2→CO2+\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 【2】 H2O\text{H}_2\text{O}

Answer

2
According to the law of conservation of mass, the total number of atoms for each element must be equal before and after the reaction. The reactant side contains 1 carbon atom, 4 hydrogen atoms, and 4 oxygen atoms. On the product side, CO2\text{CO}_2 contains 1 carbon atom and 2 oxygen atoms. Placing a coefficient of 2 in front of H2O\text{H}_2\text{O} provides the remaining 4 hydrogen atoms and 2 oxygen atoms, fully balancing the equation.

Step-by-Step Solution

1
Count the number of atoms of each element on the reactant side.
Reactants have 1 carbon atom, 4 hydrogen atoms (from CH4\text{CH}_4), and 4 oxygen atoms (from 2O22\text{O}_2).
The law of conservation of mass requires the number of atoms of each element to be identical on both sides of a balanced chemical equation.
2
Count the atoms present in the products and determine the coefficient needed for H2O\text{H}_2\text{O}.
One molecule of CO2\text{CO}_2 contains 1 carbon atom and 2 oxygen atoms. To balance the 4 hydrogen atoms and remaining 2 oxygen atoms, 2 molecules of H2O\text{H}_2\text{O} are required.
A coefficient of 2 provides 2×2=42 \times 2 = 4 hydrogen atoms and 2×1=22 \times 1 = 2 oxygen atoms, giving a total of 4 oxygen atoms on the product side.

Key Concept

Balancing chemical equations using conservation of mass
Estimated Time:45s
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Topics

Chemical Reactions and Compounds

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