Question Video: Identifying Which Set of Reaction Conditions Will Have the Fastest Rate of Reaction Science

Which of these reactions between calcium metal and nitric acid will have the fastest rate of reaction? [A] Experiment 1 [B] Experiment 2 [C] Experiment 3 [D] Experiment 4 [E] Experiment 5

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Video Transcript

Which of these reactions between calcium metal and nitric acid will have the fastest rate of reaction? (A) Experiment one, (B) experiment two, (C) experiment three, (D) experiment four, (E) experiment five.

The question describes a reaction between calcium metal and nitric acid. A reaction between these species will occur when reactant particles collide with sufficient energy and the correct orientation. How quickly the reaction takes place can be expressed by the rate of reaction.

Rate of reaction measures how reactant or product concentration, mass, or volume changes over time. As reactions occur when particles successfully collide, if the number of collisions increases, then the chance of a successful collision will increase and the rate of reaction will increase. There are a number of factors that can affect the number of collisions between reactant particles. So let’s take a look at the conditions used in this experiment.

We can see that all of the experiments use the same volume of nitric acid solution. But the concentrations of the nitric acid solutions are different. We also see that the experiments are run at different temperatures. No mention is made of the amount of calcium metal used. So we’ll assume that it’s the same for each experiment. To answer the question, we need to know how concentration and temperature affect the number of collisions between particles and therefore the rate of reaction.

Let’s start by considering concentration. Concentration is the amount of substance in a particular volume. When the concentration is low, there will be fewer particles available to collide and the number of collisions will be relatively low. As the concentration increases, the number of particles available to collide will increase and the number of collisions will increase. So increasing the concentration will increase the rate of reaction. This means that experiments two, four, and five will have a faster rate of reaction than experiments one and three. As we want to know which experiment has the fastest rate of reaction, we can eliminate answer choices (A) and (C).

Now let’s consider the effect temperature has on the rate of reaction. At low temperatures, the particles move slower and collide with less energy. As the temperature increases, the particles gain energy and move faster. As the particles are moving faster and with more energy, the particles will collide more often and are more likely to collide with sufficient energy for a reaction to occur. So increasing the temperature will increase the rate of reaction. Since experiment two is performed at a higher temperature than experiments four and five, it should have the fastest rate of reaction.

Therefore, the reaction between calcium metal and nitric acid that will have the fastest rate of reaction is experiment two, answer choice (B).

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