Which statement best defines spontaneous combustion?

Which statement best defines spontaneous combustion?

• A. A fast chemical reaction that generates heat
• B. A physical process with no chemical change
• C. A slow chemical reaction that generates heat
• D. A chemical reaction that requires an external flame

Answer: (C)

Spontaneous combustion occurs when a material undergoes slow chemical oxidation that releases heat. If that heat isn’t dissipated, the temperature can rise until the material ignites, even though no external flame is involved. The key idea is that the process is chemical and self-starting, with heat build-up driving eventual ignition. That’s why the best statement is that it’s a slow chemical reaction that generates heat. It’s not a fast reaction, it’s not purely a physical change, and it doesn’t require an external flame to begin. An example is oily rags that heat up as oils oxidize; if the heat isn’t removed, they can ignite on their own.

Spontaneous combustion occurs when a material undergoes slow chemical oxidation that releases heat. If that heat isn’t dissipated, the temperature can rise until the material ignites, even though no external flame is involved. The key idea is that the process is chemical and self-starting, with heat build-up driving eventual ignition.

That’s why the best statement is that it’s a slow chemical reaction that generates heat. It’s not a fast reaction, it’s not purely a physical change, and it doesn’t require an external flame to begin. An example is oily rags that heat up as oils oxidize; if the heat isn’t removed, they can ignite on their own.