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Question Video: Identifying from a Graph in Which Reaction the Surface Area of a Solid Was Greatest Science

In an experiment, a student added a sample of a solid into a solution, resulting in a chemical reaction. The student repeated the experiment 5 times but changed the surface area of the solid. The graph showing how the concentration of one of the products changes over time for each experiment is shown below. In which experiment was the surface area of the solid the greatest?

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Video Transcript

In an experiment, a student added a sample of a solid into a solution, resulting in a chemical reaction. The student repeated the experiment five times but changed the surface area of the solid. The graph showing how the concentration of one of the products changes over time for each experiment is shown below. In which experiment was the surface area of the solid the greatest?

In the experiment in this question, a solid was added to a solution, and the solid reacted. The concentration of a product of this reaction was graphed over time. Each of the lines on this graph represents the same reaction with the same mass of solid. The only difference is the surface area of the solid. We need to figure out which of these lines represents the experiment where the surface area of the solid was the greatest. In a solid, only particles on the surface can react. If we increase the surface area, more solid particles are exposed and available to react. This means the reaction will occur more quickly if the surface area is larger. So the experiment where the solid had the largest surface area will also be the experiment where the reaction occurs the fastest.

Looking at this graph, we can see that each line reaches the same maximum value for the concentration of the product, about 1.5 moles per liter. But each line took a different amount of time to reach 1.5 moles per liter. The red line got there first. The pink line took the longest to get there. In other words, the red line was the experiment where the reaction happened the fastest and the pink line was the experiment where the reaction happened the slowest. As we said, the fastest reaction will correspond to the greatest surface area. So the red line represents the experiment where the surface area of the solid was the greatest, making answer choice (B) the correct answer.

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