Gizmos Student Exploration| Nuclear Reactions Answer Key [100% correct]

2019

Name: ______________________________________ Date: ________________________

Student Exploration: Nuclear Reactions

[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?

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:

Hydrogen-1 Carbon-12 Uranium-235

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?

2. Colliding particles don¶t alZa\s react. Click Reset, and then click Fire neutron.

A. Does a reaction occur?

B. Explain:

Isotope Protons Neutrons

Hydrogen-1 1 0

Carbon-12 6 6

Uranium-235 92 143

Alexa Nissim 6420

H E

No

The isotope number is equal to the sum of the protons and neutrons.

Proton joins nucleus

Neutron traveled through the nucleus

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Activity A:

Proton-proton

chain

Get the Gizmo ready:

x Click Reset.

x 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?

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 observed, write in the equation for this reaction in the Gizmo and below.

A. Turn on Show equation. Was your predicted equation correct?

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?

(Activity A continued on next page)

Neutron Positron Electron Proton

i H H 9 et

yes

1.44MeV

Proton converts to neutron, positron emitted

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Activity A (continued from previous page)

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.

A. Turn on Show equation. Was your predicted equation correct?

B. Correct your equation if necessary. How much energy was emitted?

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?

B. Correct your equation if necessary. How much energy was emitted?

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 step

(H-2 created)

Second step

(He-3 created)

Last step

(He-4 created) Total energy

First He-3 atom

Second He-3 atom

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.

IH 3 He

yes

5.49MW

He He IH IH

yes

12.86MeV

1.44MW

1.44MW

5.49Mev

5.49Mev

12.89MW 26.72MW

HtiH fHt Yet

HtHt 3HtiH

Ht H TH t Ye

2

Ht 3HtiHtH

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Activity B:

CNO Cycle

Get the Gizmo ready:

x In the Reaction menu, select CNO cycle.

x 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?

B. Turn on Write equation. In the space below and in the Gizmo, write a balanced

equation for this reaction. Then, turn on Show equation to check your work.

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

2

3

4

5

6

(Activity B continued on next page)

IH 3N

IH 3N 1.95MW

C Yet 2.20MW

H IN 7.54MW

I H IO 7.35MW

Y N 9 et 2.73MW

IH IC He 4.96MW

Proton fuses with nucleus

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Activity B (continued from previous page)

3. Calculate: What is the total energy emitted by the CNO cycle?

How does this value compare to the energy released in the proton-proton chain?

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?

B. How does the net equation for the CNO

cycle compare to the net equation for the

proton-proton chain?

C. How does this help explain what you observed in question 4 above?

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?

_________________________________________________________________________

_________________________________________________________________________

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?

_________________________________________________________________________

_________________________________________________________________________

26.73MeV

4 H I He4 t let

It is greater

Other elements besides H

The energy of this lower

The CNO cycle requires carbon to be present to act as a catalyst. Also, because

the steps involve protons fusing with carbon and heavier nuclei, the CNO cycle

requires a much higher temperature,

There could be complications with the fusing.

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Activity C:

Fission

Get the Gizmo ready:

x Select Fission from the Reaction menu.

x 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.

How much energy was released?

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:

Energy:

Energy:

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.

_________________________________________________________________________

_________________________________________________________________________

(Activity C continued on next page)

197MW

on j Te Yo2r 3 on

f n Y Ba 9 Kr 3 on Homer

f n Y Ba f Kr 2 on zoomer

o n EI Te 9440 Zr 3 o n immer

Neutron hits the nucleus. Uranium split into two 2 smaller atoms.

No they are not balanced because they do not have the same number

of positive charges and the same mass on both sides of the equation.

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Activity C (continued from previous page)

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?

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: CNO cycle: Fission:

Based on these numbers, which reaction yields the most energy?

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 Energy released Mass of reactants Energy/amu

Proton-proton 4 amu (4 H-1 atoms)

CNO cycle 4 amu (4 H-1 atoms)

Fission 235 amu (U-235)

Based on this table, does fission or fusion release the most energy per amu?

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:

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?

26.72MW 26.73MeV 189MeV

fission

26.72MW 6.68amu

26.73MeV 6.6825amu

189MeV 8043amu

fusion

I think that this reaction will cause another reaction to react.

Fusion creates more power than a fission reaction. Therefore the

energy would be cheaper.

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