Which is the correct balanced equation for the complete combustion of ethane in excess oxygen?
哪种方程是乙烷在过量氧气中完全燃烧的正确平衡方程？

Question

BlackTom AI · Accepted Answer

Complete combustion of ethane yields carbon dioxide and water; balancing requires conservation of C, H, and O atoms.

1. Relevant knowledge points and concepts
- Complete combustion of a hydrocarbon CxHy produces CO2 and H2O.
- Chemical equations must conserve atoms of each element.
- Coefficients must be whole numbers (fractions allowed temporarily but final equation should use integers).

2. Step-by-step reasoning
Start with the unbalanced skeleton:
C2H6 + O2 → CO2 + H2O
Assign coefficients: a C2H6 + b O2 → c CO2 + d H2O
Balance each element.

3. Calculations and intermediate steps
- Carbon: 2a = c  → c = 2a
- Hydrogen: 6a = 2d → d = 3a
- Oxygen: each O2 has 2 O atoms, so 2b = 2c + d
 Substitute c and d in terms of a:
 2b = 2(2a) + 3a = 4a + 3a = 7a
 Thus b = 7a/2

Choose the smallest integer a to eliminate fractions. If a = 1, b = 7/2 = 3.5 (fractional). Multiply all coefficients by 2 to get integers:
a = 2 → c = 4, d = 6, b = 7
So the balanced equation is:
2 C2H6 + 7 O2 → 4 CO2 + 6 H2O

4. Why this answer is correct
Counting atoms confirms balance:
- Carbon: left 2×2 = 4, right 4×1 = 4
- Hydrogen: left 2×6 = 12, right 6×2 = 12
- Oxygen: left 7×2 = 14, right (4×2) + (6×1) = 8 + 6 = 14
All elements are conserved and coefficients are integers.

5. Why other (incorrect) forms are wrong
- Writing C2H6 + O2 → CO2 + H2O without coefficients is unbalanced.
- C2H6 + 3.5 O2 → 2 CO2 + 3 H2O is atom-balanced but uses a fractional coefficient for O2; we prefer integer coefficients, so multiply by 2 to obtain the integer-balanced equation.
- Any equation that produces CO or C (soot) would represent incomplete combustion, not complete combustion.

6. Conclusion
The balanced equation for complete combustion of ethane in excess oxygen is:
2C2H6 + 7 O2 → 4 CO2 + 6 H2O
This matches the provided correct answer.

Which is the correct balanced equation for the complete combustion of ethane in excess oxygen? 哪种方程是乙烷在过量氧气中完全燃烧的正确平衡方程？ Single choice

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