Question Video: Identifying the Reason Flour Dust Reacts Rapidly With Oxygen | Nagwa Question Video: Identifying the Reason Flour Dust Reacts Rapidly With Oxygen | Nagwa

Question Video: Identifying the Reason Flour Dust Reacts Rapidly With Oxygen Chemistry • Third Year of Secondary School

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Dust explosions in flour mills are a serious safety concern. Why is the reaction between the flour particles and the oxygen in the air so fast?

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Video Transcript

Dust explosions in flour mills are a serious safety concern. Why is the reaction between the flour particles and the oxygen in the air so fast? (A) The flour dust is highly flammable and concentrated in the air. (B) Dust explosions create pressure pockets in the air, increasing the rate of reaction. (C) The flour dust acts as a catalyst. (D) A dust explosion is exothermic. Or (E) the flour dust has a large surface area resulting in a high collision rate.

Let’s have a closer look at our answer choices.

In answer choice (A), it makes sense that dust explosions occur because flour dust is highly flammable. However, flour dust in the air is not as concentrated or, in other words, present in higher amount per space than the flour stored or on a surface. So we can eliminate answer choice (A).

Answer choice (B) refers to pressure pockets speeding up the dust explosions. However, these pockets of pressure are formed once the dust explosions begin. While increased pressure can increase the rate of a reaction, this does not explain the fast initial reaction. We can eliminate answer choice (B).

Answer choice (C) suggests that the flour dust behaves as a catalyst in the reaction. A catalyst is a substance that increases the rate of a reaction without undergoing a permanent chemical change itself. The question indicates that the dust explosion is the reaction between the flour dust and oxygen. A catalyst is not a reactant in the reaction it speeds up, so we can eliminate answer choice (C).

Answer choice (D) describes these dust explosions as exothermic. In an exothermic reaction, heat is released to the surroundings. The reaction between flour particles and oxygen is a combustion that releases a lot of heat, which makes it a serious safety concern. However, both exothermic and endothermic reactions can have a fast rate of reaction. So we can eliminate answer choice (D).

Answer choice (E) suggests that flour dust reacts quickly due to high surface area. For a reaction to occur, successful collisions between reactant particles must occur. And for a collision to successfully result in the formation of a product, the particles must collide with appropriate orientation and energy. This is summarized by what is called collision theory. Any change that can increase the frequency of successful collisions can increase the rate of a reaction.

For large blocks of flour with low surface area, reactions can only occur at the outer edges. When flour is in dust form, there is a high surface area available for collisions. Flour dust reacts more rapidly since there is opportunity for more particle collisions. The reaction is extremely fast and dangerous because the flour dust has a high surface area and a high collision rate with oxygen.

Therefore, the answer to this question “Why is the reaction between flour particles and the oxygen in the air so fast?” is answer choice (E). The flour dust has a large surface area resulting in a high collision rate.

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