Vocabulary: Avogadro’s number, chemical equation, chemical formula, chemical reaction,
coefficient, combination, combustion, conservation of matter, decomposition, double
replacement, molar mass, mole, molecular mass, molecule, product, reactant, single
replacement, subscript
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1. A candle is placed on one pan of a balance, and an equal weight is placed on the other pan.
What would happen if you lit up the candle and waited for a while? The candle that is lit up
would be lifted higher on the balance than an object with an equal weight. This would occur
because the candle made of wax would begin to melt due to the flame and shrink and candle as
well as lower the candle’s weight in the process.
2. Suppose the candle was placed in a large, sealed jar that allowed it to burn for several
minutes before running out of oxygen. The candle and jar are balanced by an equal weight.
In this situation, what would happen if you lit up the candle and waited? The candle in a jar
would become lighter than the object of equal weight on the other side of the scale. The energy
derived from the candle’s flame would be concealed into the lid of the jar. As the energy is
concealed to the top of the jar, it would lighten the candle.
Gizmo Warm-up
Burning is an example of a chemical reaction. The law of conservation of matter states that
no atoms are created or destroyed in a chemical reaction. Therefore, a balanced chemical
equation will show the same number of each type of atom on each side of the equation.
To set up an equation in the Chemical Equations Gizmo, type the chemical formulas into the
text boxes of the Gizmo. First, type in “H2+O2” in the Reactants box and “H2O” in the
Products box. This represents the reaction of hydrogen and oxygen gas to form water.
1. Check that the Visual display is chosen on each side of the Gizmo, and count the atoms.
A. How many hydrogen atoms are on the Reactants side? 2 Products side? 2
B. How many oxygen atoms are on the Reactants side? 2 Products side? 1
2. Based on what you see, is this equation currently balanced? No, the equation has one more
hydrogen atom on the product side than the reactant side .
, Activity A: Get the Gizmo ready:
Interpreting ● Erase the chemical formulas in each text box.
chemical formulas ● Check that the Visual displays are selected.
Introduction: To balance a chemical equation, you first need to be able to count how many
atoms of each element are on each side of the equation. In this activity, you will practice
counting the atoms that are represented in chemical formulas.
Question: How do we read chemical formulas?
1. Observe: Type “H2” into the Reactants box and hit E nter on your keyboard. Note that the
formula is shown as H2 below. The small “2” in H2 is a subscript.
A. What does the “2” in H2 represent?
The “2” which is a subscript represents the number of atoms of hydrogen.
B. In general, what do you think a subscript in a chemical formula tells you?
The subscript indicates the number of atoms of the elements written in front of it. .
C. Try typing in other subscripts next to the H, such as 3, 4, and 5. Is your answer to
question B still true? Explain.
Yes, if I type in different numbers in the subscript my answer to question b is still true.
Changing the number changes the number of atoms in the element.
2. Count: Clear the Reactants box, and type in a more complex chemical formula: “Ca(OH)2.”
Look at the number of atoms shown.
A. How many of each type of atom do you see? Ca: __1__ O: __2__ H: __2__
B. In general, what happens when a subscript is found outside of parentheses?
The subscript found on the outside of the parentheses indicates the number of atoms of the
elements within the parentheses.
C. Try typing in other subscripts next to the (OH), such as 3, 4, and 5. Is your answer to
question B still true? Explain.
Yes. my answer is still true if I add different subscripts to the (OH). Adding different
numbers changes the amount of (OH) atoms.
3. Practice: For each of the real chemical formulas below, calculate how many of each element
there are. Check your answers for the first three formulas using the Gizmo.
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