Gizmo - Student Exploration: Balancing Chemical Equations Answer key

2018

Name: ______Deborah Zhang________________________________ Date:

______1/12/21__________________

Student Exploration: Balancing Chemical Equations

Vocabulary: coefficient, combustion, compound, decomposition, double replacement, element,

molecule, product, reactant, single replacement, subscript, synthesis

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

The scouts are making s’mores out of toasted marshmallows, chocolate, and graham crackers.

1. What is wrong with the image below? __________The ingredients are unbalanced and

there is not enough to make four smores. _________________________________

2. Assuming a s’more requires two graham crackers, one marshmallow, and one piece of

chocolate, how many s’mores could you make with the ingredients shown?

_____2________

Gizmo Warm-up

In a chemical reaction, reactants interact to form products.

This process is summarized by a chemical equation. In the

Balancing Chemical Equations Gizmo, look at the floating

molecules below the initial reaction: H2 + O2  H2O.

1. How many atoms are in a hydrogen molecule (H2)? __2_

2. How many atoms are in an oxygen molecule (O2)? __2__

3. How many hydrogen and oxygen atoms are in a water molecule (H2O)?

______3__________

4. In general, what does a subscript (such as the “2” in H2) tell you about the molecule?

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2018

_______________________A subscript tells you how many atoms of an element are in a

molecule.__________________________________________________

5. A chemical equation is balanced if the number of each type of atom on the left side is equal

to the number of each type on the right side. Is this reaction balanced?

_______No_________

Activity A:

Balancing

equations

Get the Gizmo ready:

 Check that the Synthesis reaction is selected and

that all coefficients are set to one. (The

coefficients are the numbers in the boxes.)

Introduction: The equation H2 + O2  H2O is unbalanced because there are two oxygen atoms

on the reactants side of the equation, and only one on the products side of the equation. To

balance the equation, you cannot change the structure of any of the molecules, but you can

change the number of molecules that are used.

Question: How are chemical equations balanced?

1. Balance: Turn on Show histograms. The equation is balanced when there are equal

numbers of each type of atom represented on each side of the equation.

In the Gizmo, use the up and down arrows to adjust the numbers of hydrogen, oxygen, and

water molecules until the equation is balanced. When you are done, turn on Show

summary to check your answer.

Write the balanced equation here: __2___ H2 + _____ O2  ___2__ H2O

2. Solve: Turn off Show summary. Use the Choose reaction drop down menu to see other

equations, and balance them. Check your answers and then write the balanced equations.

___2__ Al + __6___ HCl  ___2__ AlCl3 + ___3__ H2

__2___ NaCl  __2___ Na + _____ Cl2

_____ Na2S + ___2__ HCl  __2___ NaCl + _____ H2S

_____ CH4 + ___2__ O2  _____ CO2 + ___2__ H2O

3. Practice: Balance the following chemical equations. (These equations are not in the Gizmo.)

A. __2___ Na + _____ Cl2  ___2__ NaCl

B. __2___ Na + ___2__ H2O  ___2__ NaOH + _____ H2

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2018

C. ___2__ Mg + _____ O2  __2___ MgO

D. __2___ KClO3  __2___ KCl + ___3__ O2

E. __2___ Al + __3___ CuO  _____ Al2O3 + ___3__ Cu

F. _____ I2 + ___2__ Na2S2O3  __2___ NaI + _____ Na2S4O6

G. ___6__ Mg + _____ P4  ___2__ Mg3P2

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2018

Activity B:

Classifying

reactions

Get the Gizmo ready:

 Turn off Show summary and Show histograms.

Introduction: Chemical equations show how compounds and elements react with one

another. An element is a substance consisting of one kind of atom, such as aluminum (Al) or

oxygen gas (O2). A compound is a substance made of more than one kind of atom, such as

water (H2O) or table salt (NaCl).

Question: How are chemical reactions classified?

1. Match: Most chemical reactions can be classified as one of four types. Using the chemical

equations in the Gizmo as a guide, match the following definitions to the type of reaction.

__B__ One reactant is broken down into two

or more products.

__E__ A fuel is combined with oxygen to

produce carbon dioxide and water.

__A__ Two or more reactants combine to

form one product.

__D__ Two compounds react to form two

different compounds.

__B__ A compound reacts with an element to

form a new compound and a different

element.

A. Synthesis

B. Decomposition

C. Single replacement

D. Double replacement

E. Combustion

2. Practice: Balance each of the chemical equations below. (Some equations may already be

in balance.) In the space to the right, classify the reaction as a synthesis, decomposition,

single replacement, or double replacement reaction.

A. ___ AgNO3 + ___ KCl  ___ AgCl + ___ KNO3 ______Double

replacement_________________

B. ___ H2O + ___ SO3  ___ H2SO4 _____Single

replacement__________________

C. _2__ KI + ___ Cl2  __2_ KCl + ___ I2

______Combustion_________________

D. __2_ NaHCO3  ___ Na2CO3 + ___ H2O + ___ CO2

_______Synthesis________________

E. ___ Zn + _2__ HCl  ___ ZnCl2 + ___ H2 ________ Combustion

___________

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2018

F. ___ BaCl2 + ___ Na2SO4  ___ BaSO4 + _2__ NaCl _________ Double

replacement ______________

G. ___ C3H8 + __5_ O2  __3_ CO2 + __4_ H2O

_______Decomposition________________

H. __2_ Al + __3_ CuCl2  __2_ AlCl3 + _3__ Cu ________ Combustion

_______________

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