Question

which best explains why sawdust burns more quickly than a block of wood of equal mass under the same conditions?
the molecules move more quickly in the sawdust than in the block of wood.
the pressure of oxygen is greater on the sawdust.
more molecules in the sawdust can collide with oxygen molecules.
oxygen is more concentrated near the sawdust than the block of wood.

Explanation:

To determine why sawdust burns faster than a wood block, we analyze reaction rates and surface area. Sawdust has a much larger surface area than a solid wood block of equal mass. A larger surface area means more wood molecules are exposed to oxygen, allowing more frequent collisions between wood (fuel) and oxygen (reactant) molecules.

• The first option is incorrect because the molecular speed (related to temperature) is the same under the same conditions.
• The second option is incorrect as oxygen pressure is the same in the same environment.
• The fourth option is incorrect because oxygen concentration is the same near both (assuming the same environment).
• The third option is correct because the larger surface area of sawdust exposes more molecules to oxygen, leading to more collisions and a faster reaction (burning).

Answer:

C. More molecules in the sawdust can collide with oxygen molecules. (Note: Assuming the options are labeled A, B, C, D with the third option being C as per the standard multiple - choice labeling. If the original options had different labels, adjust accordingly. Based on the given options in the problem, the correct one is the third option which states "More molecules in the sawdust can collide with oxygen molecules".)