The question “what is produced when cellulose burns” refers to the combustion of cellulose, a carbohydrate polymer found in wood, paper, and cotton. Under complete combustion (enough oxygen), the carbon in cellulose is oxidized to carbon dioxide and the hydrogen is oxidized to water. Heat and light are released as energy, but the chemical products are CO2 and H2O.
Step 1: Use a chemical formula for cellulose
Cellulose is a polymer, but its repeating unit is commonly written as (C6H10O5)n. Balancing is usually done for one repeat unit C6H10O5, then scaled by \(n\).
Step 2: Write the combustion skeleton
Complete combustion uses oxygen gas and produces carbon dioxide and water:
\[ \mathrm{C_6H_{10}O_5} + \mathrm{O_2} \rightarrow \mathrm{CO_2} + \mathrm{H_2O} \]
Step 3: Balance C and H first
Balance carbon: 6 carbon atoms require 6 CO2. Balance hydrogen: 10 hydrogen atoms require 5 H2O.
\[ \mathrm{C_6H_{10}O_5} + \mathrm{O_2} \rightarrow 6\,\mathrm{CO_2} + 5\,\mathrm{H_2O} \]
Step 4: Balance oxygen last
Count oxygen atoms on the products side:
\[ \text{O in }6\,\mathrm{CO_2} = 6 \times 2 = 12 \qquad \text{O in }5\,\mathrm{H_2O} = 5 \times 1 = 5 \qquad \text{Total O} = 17 \]
The reactant cellulose already contains 5 oxygen atoms, so oxygen gas must provide the remaining 12 oxygen atoms:
\[ 5 + 2x = 17 \quad \Rightarrow \quad 2x = 12 \quad \Rightarrow \quad x = 6 \]
The balanced complete-combustion equation is:
\[ \mathrm{C_6H_{10}O_5} + 6\,\mathrm{O_2} \rightarrow 6\,\mathrm{CO_2} + 5\,\mathrm{H_2O} \]
Step 5: Scale to the polymer form
For cellulose written as (C6H10O5)n, the balanced equation scales by \(n\):
\[ \mathrm{(C_6H_{10}O_5)_n} + 6n\,\mathrm{O_2} \rightarrow 6n\,\mathrm{CO_2} + 5n\,\mathrm{H_2O} \]
What changes if oxygen is limited?
In real fires, oxygen supply can be limited, temperature can vary, and side reactions can occur. Under incomplete combustion, additional products such as carbon monoxide and solid carbon (soot/char) can form alongside water, and smoke may contain many partially oxidized organic fragments.
| Burning condition | Main chemical products | Typical observation |
|---|---|---|
| Excess oxygen (complete combustion) | CO2(g) and H2O(g) | Cleaner flame, less smoke; most carbon ends as CO2 |
| Limited oxygen (incomplete combustion) | H2O(g) plus CO(g) and/or C(s) (soot), with some CO2 | More smoke/soot; carbon not fully oxidized |
| Very low oxygen (smoldering/pyrolysis influence) | Char/ash and a mixture of volatile organic compounds, plus some H2O | Smoldering, heavy smoke; residue (char) remains |
Summary for “what is produced when cellulose burns”: under complete combustion, the chemical products are CO2 and H2O; under incomplete combustion, CO and soot/char can also be produced.