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Question Video: Choosing Which Chemical Reaction is Likely to Occur on a Certain Timescale Science

The chemical timeline gives examples of different chemical reactions that take place over a range of timescales. Which of the following reactions is likely to occur at point X? [A] Cooking food [B] The reaction of iron and hydrochloric acid [C] Striking a match [D] The reaction of alkali metals with water [E] The chemical weathering of rocks

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Video Transcript

The chemical timeline below gives examples of different chemical reactions that take place over a range of timescales. Which of the following reactions is likely to occur at point X? (A) Cooking food, (B) the reaction of iron and hydrochloric acid, (C) striking a match, (D) the reaction of alkali metals with water, or (E) the chemical weathering of rocks.

Looking at the provided diagram, we can see that X corresponds to a reaction which is very slow. The diagram doesn’t provide any information about how slow this reaction is. However, we do know that this reaction must be slower than the rusting of iron. Let’s take a look at each of the answer choices and see if we can relate the speed of these reactions to the rusting of iron.

Option (A) is cooking food. While there are a number of chemical reactions involved in cooking food and the time it takes depends on the type of food being prepared, most food can be cooked in a matter of minutes or a few hours. So cooking food is unlikely to be slower than the rusting of iron. This means we can eliminate answer choice (A).

Answer choice (B) is the reaction of iron and hydrochloric acid. When hydrochloric acid is added to iron, bubbles immediately start to form, indicating that a reaction is occurring. The reaction between iron and hydrochloric acid occurs quite quickly. So answer choice (B) cannot be the answer to this question.

Answer choice (C) is striking a match. When a match is struck, the match immediately begins to burn, a sign of a chemical reaction. So striking a match is a very fast reaction. This means that answer choice (C) cannot be the answer to this question.

Answer choice (D) is the reaction of alkali metals with water. When an alkali metal like sodium is added to water, an extremely vigorous explosive reaction occurs. So the reaction of alkali metals with water is very fast. This means we can eliminate answer choice (D).

This leaves us with answer choice (E) the chemical weathering of rocks. The chemical weathering of rocks may be due to water or acid rain dissolving the minerals that make up the rocks or oxygen in the air reacting with metals in the rocks to form metal oxides. In general, the chemical weathering of rocks is a slow process that can take several years. As this process is very slow, the reaction which is likely to occur at point X is answer choice (E) the chemical weathering of rocks.

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