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.
