Student Exploration: Balancing Chemical Equations

Student Exploration: Balancing Chemical Equations
Vocabulary: coefficient, 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.
What is wrong with the image below?
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?

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 à H2O.
How many atoms are in a hydrogen molecule (H2)?
How many atoms are in an oxygen molecule (O2)?
How many hydrogen and oxygen atoms are in a water molecule (H2O)?
In general, what does a subscript (such as the “2” in H2) tell you about the molecule?
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? __ ______________
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 à H2O is unbalanced because there are two oxygen atoms on the reactants side of the equation, and only one on the productsside 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?
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: _____ H2 + _____ O2 à _____ H2O
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.

_____ Al + ____ HCl à _____ AlCl3 + _____ H2

_____ NaCl à _____ Na + _____ Cl2

_____ Na2S + _____ HCl à _____ NaCl + _____ H2S

Practice: Balance the following chemical equations. (These equations are not in the Gizmo.)
_____ Na + _____ Cl2 à _____ NaCl
_____ Na + _____ H2O à _____ NaOH + _____ H2
_____ Mg + _____ O2 à _____ MgO
_____ KClO3 à _____ KCl + _____ O2
_____ Al + _____ CuO à _____ Al2O3 + _____ Cu
_____ CaCO3 à _____ CaO + _____ CO2
_____ I2 + _____ Na2S2O3 à _____ NaI + _____ Na2S4O6
_____ Mg + _____ P4 à _____ Mg3P2
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?
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.


____ One reactant is broken down into two or more products.

____ Two or more reactants combine to form one product.

____ Two compounds react to form two different compounds.

____ A compound reacts with an element to form a new compound and a different element.
Synthesis
Decomposition
Single replacement
Double replacementPractice: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.
___ AgNO3 + ___ KCl à ___ AgCl + ___ KNO3             _______________________
___ H2O + ___ SO3 à ___ H2SO4                                  ___ ____________________
___ KI + _1__ Cl2 à ___ KCl + ___ I2                            _______________________
___ NaHCO3 à ___ Na2CO3 + ___ H2O + ___ CO2        ____ ___________________
___ Zn + ___ HCl à ___ ZnCl2 + ___ H2                                   _______________________
___ BaCl2 + ___ Na2SO4 à ___ BaSO4 + ___ NaCl       ______
___ Ag2O à ___ Ag + ___ O2                                       ___ ____________________
___ Al + ___ CuCl2 à ___ AlCl3 + ___ Cu                    
What two things did you learn about balancing equations from completing this Gizmo lab? (Please use complete sentences.) Two things I learned is how to balance chemical equations and the terms reactants and products.
When a combustion reaction occurs, a hydrocarbon reacts with oxygen and produces carbon dioxide and water.  
Balance this combustion reaction:     CH4  +   O2    --->    CO2  +    H2O

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