Collision Theory Gizmo Answer Key

Name: Steven Clarke Date: 05-02-2022 Student Exploration: Collision Theory Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: activated complex, catalyst, chemical reaction, concentration, enzyme, half-life, molecule, product, reactant, surface area Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. Suppose you added a spoonful of sugar to hot water and another to ice-cold water. Which type of water will cause the sugar to dissolve more quickly? The hot water 2. Suppose you held a lighted match to a solid hunk of wood and another match to a pile of wood shavings. Which form of wood will catch fire more easily? Timber shavings Gizmo Warm-up A chemical reaction causes the chemical compositions of substances to change. Reactants are substances that enter into a reaction, and products are substances produced by the reaction. The Collision Theory Gizmo allows you to experiment with several factors that affect the rate at which reactants are transformed into products in a chemical reaction. You will need blue, green, and orange markers or colored pencils for the first part of this activity. ✏️ 1. Look at the key at the bottom of the SIMULATION pane. In the space below, draw ( ) the two reactants and two products of this chemical reaction. ✏️Reactants: 2. Click Play ( ). What do you see? ✏️Products: Since no products were generated and reactant A just bounced off reactant B, the reaction does not occur. Get the Gizmo ready: Activity A: Temperature ● Click Reset ( ). ● Check that the Reactant concentration is set to 1.0 mol/L, the Catalyst concentration is set to 0.00 mol/L, and the Surface area is Minimum. Question: How does temperature affect the rate of a chemical reaction? 1. Observe: Select the ANIMATION tab. View the animation with No catalyst selected. What do you see? The products A and B are created as a result of the reactants colliding. When two reactant molecules meet, they form a temporary structure called an activated complex. The activated complex breaks up into the product molecules. 2. Observe: Return to the CONTROLS pane. Set the Temperature to 0 °C and the Simulation speed to its maximum setting. Click Play. A. Describe the motions of the molecules. Reactant A are only moving and bouncing off of either reactant Bs or one another. While the reactant B's are simply vibrating together in a group. B. Now set the Temperature to 200 °C. How does increasing the temperature affect the motions of the molecules? The reaction is occurring more quickly as a result of the reactant A's more aggressive movement. C. What do you notice about the chemical reaction at the higher temperature? The reaction takes place faster 3. Interpret: Select the GRAPH tab. Click the zoom out button (–) until you can see the whole graph. What does this graph show? As the concentration of the products rises over time, the concentration of the reactants falls. 4. Predict: How do you think temperature will affect the rate of a chemical reaction? The pace of reaction is accelerated by temperature because it raises both the frequency of collisions and the kinetic energy of the reactants. 5. Gather data: Click Reset. A useful way to compare reaction rates is to record the time required for half of the reactants to react, called the half-life of the reaction. With the Temperature set to 200 °C, click Play. Click Pause ( ) when the number of reactant molecules is 10. Record the half-life time in the first space of the table below. Trial 200 °C 150 °C 100 °C 50 °C 1 482 402 1262 6962 2 262 482 1922 4322 Mean half-life 372 442 1592 5668 Repeat the experiment at different temperatures to complete the table. (Note: To get exact times, you can refer to the TABLE tab.) 6. Calculate: Calculate the mean half-life for each temperature. Fill in these values above. (Hint: To get an exact mean, first convert each time to seconds by multiplying the minutes value by 60 and adding this to the seconds. To find the mean in seconds, add up the two times and divide by two. Convert the answer back to minutes and seconds.) 7. Analyze: What do your results indicate? The rate of reaction quickens/occurs more quickly with increasing temperature. 8. Draw conclusions: For two molecules to react, they must collide at just the right angle and with enough energy to break the original bonds and form new ones. Based on these facts, why does the reaction tend to go more quickly at higher temperatures? The molecules heat up and move more quickly as a result of the high temperature, which increases their kinetic energy and leads them to move more quickly and break bonds. 9. Apply: Paper must be heated to 234 °C to begin reacting with oxygen. This can be done by putting the paper over a flame. Why do you think the paper must be heated to start burning? Because the reactants must have enough, or equal, energy to the activation energy in order to burn the paper, the paper must first be heated before burning. Therefore, by heating the paper, you enable the reaction to cross the activation energy boundary and begin burning by increasing the impact frequency and kinetic energy. Activity B: Surface area and concentration Get the Gizmo ready: ● Click Reset. ● Check that the Catalyst concentration is set to 0.00 mol/L and the Surface area is Minimum. ● Set the Temperature to 200 °C. Introduction: Reaction rates are also influenced by surface area and concentration. The surface area of a solid is a measure of how much of the solid is exposed to other substances. The concentration of a substance is a measure of how many molecules of that substance are present in a given volume. Question: How do surface area and concentration affect reaction rates? 1. Observe: Change the Surface area from Minimum to Maximum. You can imagine that a solid reactant has been dissolved in a liquid. How does this change how many Reactant B molecules are exposed to Reactant A? More reactant A's can collide with reactant B's and produce products as a result. 2. Predict: How do you think increasing the surface area will affect the rate of the reaction? Since there is more surface area of reactant B for reactant A to collide with and create product on, the reaction will proceed at a faster rate. 3. Gather data: Set the Reactant concentration to 2.0 mol/L. Use the Gizmo to measure the half-life of the reaction for each surface area setting. (There will now be 20 reactant molecules left at the half-life.) Then, calculate the mean half-life for each setting. Trial Minimum surface area Maximum surface area 1 282 62 2 172 18 Mean half-life 227 40 4. Analyze: What do your results indicate? You greatly improve the rate of response by increasing the surface area. 5. Explain: Why does the reaction proceed more quickly when the surface area is increased? Increased surface area allows for more angles and faces for reactant A and reactant B to contact with, increasing the frequency of collisions, which speeds up the reaction process. 6. Observe: Click Reset. Move the Reactant concentration slider back and forth. What do you notice? In the reaction, the number of reactants fluctuates. 7. Predict: How will increasing the reactant concentration affect the rate of the reaction? Why? By allowing more reactants to collide, the concentration of reactants will rise, increasing the frequency of collisions, which will speed up the reaction. 8. Gather data: Make sure the Temperature is 200 °C and the Surface area is Maximum. Use the Gizmo to measure the half-life for each given reactant concentration. (Note that the number of reactant molecules changes with each concentration.) Calculate the means. Trial 0.4 mol/L 0.8 mol/L 1.2 mol/L 1.6 mol/L 2.0 mol/L 1 72 102 50 42 72 2 342 172 112 114 34 Mean half-life 207 137 81 78 53 9. Compare: If possible, find the mean times for each concentration for your entire class. What is the mean class time for a concentration of 0.4 mol/L? How about for 2.0 mol/L? Mean for 0.4 mol/L: 207 sec Mean for 2.0 mol/L: 53 sec 10. Analyze: What do these results indicate? Since the frequency of collisions increases with an increase in reactant concentration, the reaction rate also increases. 11. Apply: Hydrochloric acid reacts with the mineral calcite to produce carbon dioxide gas, water, and calcium chloride. Based on what you have learned in activity A and activity B, what are three things you could do to make the reaction occur more quickly? Increase the temperature, increase the reactants concentration and finally increase the surface area. Activity C: Get the Gizmo ready: Catalysts ● Click Reset ( ). Introduction: A catalyst is a substance that helps a chemical reaction to proceed. The catalyst molecules are not changed by the reaction and can be reused over and over again. Question: How do catalysts affect the rate of a chemical reaction? 1. Observe: Select the ANIMATION tab. Select With catalyst, and observe. A. What do you see? The catalyst speeds up the reaction by causing the reactants to attract to one another more quickly. B. Why do you think the shape of a catalyst is important? As a result, the catalyst itself need not be involved in the reaction, and the reactants can clash at a specified angle. Many catalysts have a special shape that allows them to bind to specific reactant molecules. 2. Predict: How do you think catalysts will affect the rate of a chemical reaction? Increase reaction rate while lowering activation energy. 3. Gather data: On the CONTROLS pane, set the Reactant concentration to 2.0 mol/L, the Surface area to Maximum, and the Temperature to 50 °C. Measure the half-life for each given catalyst concentration. Calculate the means. Trial Catalyst concentration 0.00 mol/L 0.05 mol/L 0.10 mol/L 0.15 mol/L 1 1982 252 152 142 2 1862 322 112 75 Mean half-life 1922 287 132 109 4. Analyze: What do your results indicate? By adding catalyst, you can greatly speed up the reaction, making it happen more quickly because the catalyst lowers the activation energy. 5. Explore: Set the Catalyst concentration to 0.00 mol/L and the Temperature to 0 °C. Click Play, wait for 10 minutes of simulated time, and click Pause. A. What happens? The reaction is very slow (34 reactants and 6 products) B. Click Reset, set the Catalyst concentration to 0.25 mol/L, and click Play. After 10 simulated minutes, click Pause. What happens now? Before barely 10 minutes had passed, the reaction was complete. C. Why do you think the catalysts allowed the chemical reaction to take place at 0 °C? When the temperature was 0 degrees, the catalyst offered a brief channel for the reaction, allowing the activation energy to decrease as the reaction continued to occur at 0 degrees. 6. Draw conclusions: What is the usefulness of catalysts? Permit the reaction to occur at any specified temperature or environment. 7. Apply: Most of the chemical reactions inside your body rely on protein catalysts called enzymes to take place. For example, the enzyme pepsin helps to break down protein molecules in your stomach. What might happen if your stomach stopped producing pepsin? Protein would thus be unable to be metabolized and used up; instead, it would have built up in the stomach, preventing other foods from being digested and absorbed by the intestines.