Video Transcript
Five reaction vessels are filled with two different types of gas molecules. One of the gas types has a red color. The other gas type has a blue color. This is described in the following figure. The gas molecules react when they collide with each other. Which reaction vessel should have the highest rate of reaction? You can assume that all of the reaction vessels have the same temperature.
Collision theory tells us that reactions can only occur when particles collide with sufficient energy and the correct orientation. The rate at which a reaction occurs is measured by the frequency of successful collisions. In other words, the rate of reaction is how quickly reactant particles can successfully collide to form product particles. The frequency of these successful collisions can be influenced by many different factors, such as temperature, pressure, concentration of particles, surface area of particles, or the presence of a catalyst.
We are told that all five reaction vessels have the same temperature. We can also see that the surface area of the particles in all five vessels is the same. Additionally, there is no mention in the question of the presence of a catalyst. These factors cannot be used to determine which of the five vessels has the highest rate of reaction. Let’s focus then on pressure and concentration.
Concentration is often used to discuss solutions and can be defined as the amount of solute per volume of solution. Concentration can be calculated by finding the number of particles per volume of space. If we look at our five reaction vessels, we can see that they are the same size. So we can assume that they have the same volume. When dealing with gases, pressure can be defined as the force per area that gas particles exert on a surface. When volume and temperature are kept constant, the pressure and concentration of a sample of gas are directly proportional. So, under these conditions for a gas, when we increase the concentration and thus increase the pressure, we increase the likelihood of successful collisions and therefore increase the rate of reaction.
Now let’s have a look at our five reaction vessels. We can see that they vary in number of particles in same amount of space, with reaction vessel (E) having the fewest number of particles and reaction vessel (A) having the most. Reaction vessel (A) has the highest concentration of both blue and red gas molecules and would be the reaction vessel under the highest amount of pressure. Because of this, reaction vessel (A) would likely have the highest frequency of successful collisions and thus should be the reaction vessel with the highest rate of reaction. The correct answer is (A).
