Name ___________________________________________ Date__________________Period________
Balancing Chemical Equations
In this activity, you will balance a wide variety of chemical equations.
1. Begin with a simple chemical equation, combining molecular hydrogen and oxygen to make water.
At the top of the Gizmotm, click in the white rectangle under Reactants. Using capital letters, type
H2 + O2, and then hit Enter on your keyboard. The Gizmo will interpret this as H2 + O2. Then,
click under Products and enter in H2O.
1. Observe the pictures of atoms in the boxes. How many total hydrogen atoms are there in
the Reactants box? How many oxygen atoms are there?
2. How many hydrogen and oxygen atoms are there in the Products box? Are there the same
number of hydrogen atoms in the Reactants and Products boxes? Are there the same
number of oxygen atoms in the Reactants and Products boxes?
3. Is your current equation balanced? Explain why or why not.
2. As you can see, there is one less oxygen atom in the Products box than the Reactants box. This
violates the Law of Conservation of Mass. To solve this problem, you need to change the number
of molecules that go into and come out of the reaction.
1. To balance equations, you can add coefficients to the reactants and products. Changing the
subscripts is not allowed because compounds have specific formulas. For example, water
always consists of two hydrogen atoms bonded to one oxygen atom. You will never find
water that has the formula HO, H3O, or HO2! In the white Products rectangle, place the
cursor in front of the H2O, type the number 2, and then hit Enter on your keyboard. Are
the oxygen atoms balanced now?
2. Now the oxygen atoms are equal, but the hydrogen atoms are no longer balanced. How
many H2 molecules are needed to produce four hydrogen atoms? Type this number in front
of H2 in the white Reactants rectagle. Hit Enter. Is the equation balanced now? Explain
why or why not.
3. In the dropdown menu below the Reactants box, change the selection from Visual to
Numerical. Do the same for the Products box. This view may be easier to use when the
equations become more complex and individual atoms are harder to count. Another useful
view is Histogram, which shows the numbers in graphical form.
4. To check your equation, click the Show if balanced checkbox. Is the equation properly
balanced? If not, change the coefficients until the equation is balanced.
5. There is more than one set of coefficients that would balance this equation. Can you think
of another?
3. Now try the more complex reaction between calcium hydroxide and hydrobromic acid. Deselect
Show if balanced by clicking in the box. In the white Reactants rectangle, delete the previous
formula. Paying attention to uppercase and lowercase letters, type in Ca(OH)2 + HBr, and hit
Enter. In the Products rectangle, type CaBr2 + H2O. Select your preferred view in the dropdown
menus.
1. Look at the formula for calcium hydroxide, Ca(OH)2. This indicates that there are two
oxygen atoms and two hydrogen atoms in a molecule of calcium hydroxide. How many
oxygen and hydrogen atoms are in a molecule of Al(OH)3?
2. Look at the numbers of atoms in the Reactants and Products boxes. Of the four elements
involved in the reaction, which ones are not balanced?
3. There is one bromine (Br) atom on the reactants side, and two on the products side. Add a
coefficient in front of HBr (and hit Enter) to balance the bromine atoms. Are there equal
numbers of bromine atoms now? If not, change the coefficient of HBr until the bromines
are balanced.
Name ___________________________________________ Date__________________Period________
4. Now add a coefficient in front of H2O to balance the hydrogen and oxygen atoms. Are they
balanced now? Are the calcium atoms balanced? Check Show if balanced to see if you are
correct.
4. Practice balancing some of the chemical equations from the list below. Remember that you can
only change the coefficients! You can also make up your own equations to balance, but be aware
that not every reaction you come up with actually occurs.