Nuclear Reactions Gizmo Answer Key

Name: Dashawn Haynes Date: 05-17-22 Student Exploration: Nuclear Reactions Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. [Note to teachers and students: This Gizmo was designed as a follow-up to the Nuclear Decay Gizmo. We recommend doing that activity before trying this one.] Vocabulary: chain reaction, CNO cycle, catalyst, deuterium, electron volt, fission, fusion, isotope, nuclear reaction, positron, positron emission, proton-proton chain Prior Knowledge Questions (Do these BEFORE using the Gizmo.) The chart to the right gives the isotope name, element name, number of protons, and number of neutrons of three isotopes. 1. What do you notice about the isotope number and the sum of protons and neutrons? The protons and neutrons combined make up the same isotope. ✏️ 2. The element symbol for uranium-238 is . This means U-238 has a total mass of 238 and contains 92 protons. Write the element symbols for the isotopes in the table: Gizmo Warm-up The Nuclear Reactions Gizmo simulates a particle accelerator. Particle accelerators speed up atoms to very high velocities, then crash the atoms together with enough energy to cause changes called nuclear reactions. There are three particle beams available in this Gizmo, protons, neutrons, and helium-3 nuclei. 1. Click Fire Proton to engage the first particle beam. What happens? The proton is taken up by the nucleus. 2. Colliding particles don’t always react. Click Reset, and then click Fire neutron. A. Does a reaction occur? No B. Explain: While traversing the nucleus, the neutron did not combine. Get the Gizmo ready: Activity A: Proton-proton chain ● Click Reset. ● Be sure Proton-proton is selected in the Reaction menu. Introduction: All stars turn hydrogen into helium in a process called nuclear fusion. Stars perform this process in different ways. In stars like our sun, the proton-proton chain is used. This reaction requires temperatures greater than 4,000,000 K to occur. Question: How does the process of fusion turn hydrogen into helium in stars? 1. Observe: Click Fire proton and observe. What happens after the proton merges into the nucleus? Positron is emitted as well as a proton is converted into a neutron. This is a form of nuclear decay called positron emission. During positron emission, a proton decays into a neutron. In this process, it emits a positron, which is a nearly massless antimatter particle with a positive charge. 2. Observe: Click Reset and click Fire proton. Observe what happens. Many subatomic particles appear frequently in nuclear reactions. Their element symbols are given below: (Neutrinos are also produced but are beyond the scope of this Gizmo.) ✏️ Click Reset and click Fire proton. Turn on the Write equation checkbox. Based on what you have write in the equation for this reaction in the Gizmo and below. observed, A. Turn on Show equation. Was your predicted equation correct? Yes Correct your equation if necessary. The resulting H-2 isotope is called deuterium. B. Emitted energy is reported in megaelectron volts (MeV), where one MeV is equal to one million electron volts. How much energy is emitted in this reaction? 1.44 MeV 3. Hypothesize: Click Next. In the next step, another proton will be fired at the hydrogen-2 atom. Make a prediction about what will happen by filling in the equation in the Gizmo and below, and then click Fire proton. Click the image then select edit to fill in the equation. ✏️ A. Turn on Show equation. Was your predicted equation correct? Yes B. Correct your equation if necessary. How much energy was emitted? 5.49 Mev ✏️ 4. Apply: Click Next. The last step in this cycle involves two helium-3 atoms reacting. Click Fire He-3. Observe what happens, and then write an equation to describe this process. A. Turn on Show equation. Was your predicted equation correct? Yes B. Correct your equation if necessary. How much energy was emitted? 12.86 MeV 5. Calculate: To find the total energy emitted in the proton-proton chain, you have to consider the fact that two He-3 atoms must be created to form the final He-4 atom. Write the energy produced in each step, and then find the sum of all of these energies using the table below. First He-3 atom Second He-3 atom First step (H-2 created) 1.44 MeV 1.44 MeV ✏️ Second step (He-3 created) 5.49 MeV 5.49 MeV Last step (He-4 created) Total energy 12.89 MeV 26.72 MeV 6. Extend your thinking: To determine the net equation for the conversion of hydrogen-1 to helium-4, list the equations for each step of the proton-proton chain in the space at right. (Write two equations for the first step and the second step, because these are repeated.) Next, cross out any elements that appear on both sides of the equation. Anything that remains makes up the net equation. Activity B: CNO Cycle Get the Gizmo ready: ● In the Reaction menu, select CNO cycle. ● Select the Write equation checkbox. Introduction: In stars larger than the Sun, the CNO cycle is the main pathway for fusion. In this reaction cycle, a heavy atom like carbon or oxygen participates in each step. At the end of one cycle, the original heavy atom has been recreated and hydrogen has been transformed into helium. This reaction begins when temperatures reach 15,000,000 K or more. Question: How do large stars form helium from hydrogen through fusion? 1. Observe: The Gizmo starts with an atom of carbon that reacts with the first hydrogen atom, and produces only one product. Click Fire proton to see what happens. A. What did you see? A gamma is released B. Turn on Write equation. In the space below and in the Gizmo, reaction. Then, turn on Show equation to check your work. ✏️write a balanced equation for this 2. Predict: Click Reset. Go through the steps of the CNO cycle. Before each step, make a prediction about what the reaction will be, and type it into the Gizmo. You can use the information in the Gizmo to help you. As you check your answers in the Gizmo, write down the correct reaction below. Record the energy emitted in each step as well. ✏️ Step Equation Energy emitted 1 1.95MeV 2 2.20MeV 3 7.54MeV 4 7.35MeV 5 2.73MeV 6 4.96MeV 3. Calculate: What is the total energy emitted by the CNO cycle? 26.73MeV How does this value compare to the energy released in the proton-proton chain? They differ by a hundredth, but they are almost identical. ✏️ 4. Analyze: As you did with the proton-proton chain, determine the net equation for the CNO cycle. In the space at right, write the equations of the CNO cycle in a column. Then, cross out any substances that appear on both sides. Write the remaining substances at the bottom. This is the net equation for the CNO cycle. ✏️ A. What is the net equation for the CNO cycle? Carbon+Nitrogen+Oxygen B. How does the net equation for the CNO cycle compare to the net equation for the proton-proton chain? Both the proton-proton chain and the CNO cycle produce one helium nucleus from four hydrogen nuclei, releasing energy. C. How does this help explain what you observed in question 4 above? Given that there is no carbon in the proton chain cycle, this helps to explain the observations from number 4. 5. Interpret: A catalyst is a substance that takes part in a reaction without being consumed. In what ways is the carbon in the first step in the CNO cycle similar to a catalyst? If protons are added, the carbon remains in the equation but is altered. 6. Make a connection: Many scientists feel that fusion would be a great way to generate electricity the future. What is the biggest obstacle to harnessing the energy of fusion? You need an extremely high amount of heat and energy to cause a fusion reaction Activity C: Fission Get the Gizmo ready: ● Select Fission from the Reaction menu. ● Be sure Write equation is turned on. Introduction: Fission is the splitting of an atom. In a fission reaction, large atoms like uranium-235 become two smaller atoms. The resulting isotopes are often radioactive, and undergo additional nuclear reactions to form a variety of products. Question: How does a nuclear reactor produce power? 1. Observe: Click Fire neutron. Describe your observations. The neutron breaks into two smaller atoms as it strikes the nucleus. How much energy was released? 197MeV ✏️ 2. Predict: Based on what you observed, write a balanced nuclear equation. Check the Show equation checkbox to check your work. Correct your equation if needed. ✏️ 3. Explore: Nuclear fission does not always result in the same products. Click Reset, and then launch another neutron. Record your observations and repeat this process. What are the three fission reactions modeled in this Gizmo, and how much energy does each produce? Energy:170MeV Energy: 200MeV Energy: 197MeV 4. Analyze: Are all of these nuclear equations balanced? In other words, do they all have the same number of positive charges and same mass on both sides of the equation? Explain. The answer is no because they don't have an equal quantity of positive charges and masses on either side. 5. Draw connections: The uranium fission reactions are triggered by a neutron, and each reaction produces two or three more neutrons. What do you think will happen next? There will be a chain reaction When the product of one reaction causes another reaction to start, it is called a chain reaction. In the case of nuclear fission, the number of atoms undergoing fission can multiply exponentially with the potential to release an enormous amount of energy. In a nuclear power plant, many safeguards are in place to keep the reaction under control. 6. Compare: In the spaces below, list the amounts of energy released by the proton-proton chain, the CNO cycle, and nuclear fission. (For fission, list the average emitted energy.) Proton-proton chain: 26.72MeV CNO cycle: 26.73MeV Fission: 189MeV Based on these numbers, which reaction yields the most energy? Fission 7. Analyze: Fission produces a lot of energy, but it involves very heavy atoms. A uranium atom has 235 times the mass of a hydrogen atom. A better way to compare the energy released in each reaction is to consider how much energy is release per atomic mass unit (amu). To find this value, divide the emitted energy by the mass of the reactants in the table below. Reaction Proton-proton CNO cycle Fission Energy released 26.72MeV 26.73MeV 189MeV Mass of reactants 4 amu (4 H-1 atoms) 4 amu (4 H-1 atoms) 235 amu (U-235) Energy/amu 6.68 amu 6.6825 amu 0.8043 amu Based on this table, does fission or fusion release the most energy per amu? Fusion (CNO Cycle) 8. Infer: Suppose the same mass of fuel was used in a fusion reaction and a fission reaction. About how many times more energy would be released by the fusion reaction? Show your work: It would be around 7.07 times more, 189/(~26.73)=~7.07 Today, nuclear power plants rely on fission. While fusion reactions have been used in nuclear bombs, many scientists and engineers hope that in the future we can use fusion to produce energy. What are some possible advantages of fusion energy over fission energy? Compared to fission, fusion produces power at a cheaper cost.