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Methane burns as CH4 + 2O2 giving CO2 + 2H2O. Which set of molecule numbers also satisfies this equation?
A1 CH4, 1 O2, 2 CO2, 2 H2O
B2 CH4, 2 O2, 2 CO2, 4 H2O
C3 CH4, 3 O2, 3 CO2, 6 H2O
D3 CH4, 6 O2, 3 CO2, 6 H2O
Answer & Solution
Correct answer: D. 3 CH4, 6 O2, 3 CO2, 6 H2O
1. The coefficients give a fixed ratio of 1:2:1:2 for methane, oxygen, carbon dioxide and water.
2. Any set of numbers in that same ratio satisfies the equation, so multiply all four by 3.
3. That gives 3 CH4, 6 O2, 3 CO2 and 6 H2O, which keeps the 1:2:1:2 pattern.
4. Options with equal numbers of CH4 and O2 break the 1:2 ratio between fuel and oxygen.
5. So only the 3-6-3-6 set works.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 4 "Stoichiometry of Chemical Reactions", section 4.1 Writing and Balancing Chemical Equations_
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