Balancing Chemical Equations

We’ve done it all – counted atoms, examined trends, bonded atoms…. But now, we’re going to string it all together in a sort of equation. – Like math…but not math. Remember the conservation of mass? – Matter cannot be created or destroyed.

CHEMICAL EQUATIONS are representations of chemical reactions. – REACTANTS are the chemicals that go into the reaction. These are listed on the left side of the equation. – PRODUCTS are the chemicals that come out of the reaction. These are listed on the right side of the equation.

Chemical equations are written much like you would write a math problem. You’re basically adding things together to make a total on the right side. But there are some differences, too. – Instead of a “=“, we use an arrow to show direction (  ). – Sometimes equations aren’t as simple as adding things up.

Let’s look at an example. 2H 2 + O 2  2H 2 O This is the reaction to form water from its elements. What kinds of terms or features do you notice in this equation? What are my reactants? What are my products?

2H 2 + O 2  2H 2 O In the formation of water (H 2 O), we react, or consume, 2 portions of hydrogen for every 1 portion of oxygen. As a result, we produce 2 portions of water. Let’s look at the atoms themselves. – Is this equation BALANCED? Are all the atoms that start the reaction present at the end? – 4 hydrogen go in, 4 hydrogen come out – 2 oxygen go in, 2 oxygen come out

Try another example: CH 4 + 2O 2  CO 2 + 2H 2 O This is the reaction for burning methane. Notice that one of the products is carbon dioxide, a greenhouse gas.

CH 4 + 2O 2  CO 2 + 2H 2 O How many carbons do we start with? – How many do we end with? How many hydrogens do we start with? – How many do we end with? How many oxygens do we start with? – How many do we end with? This equation has already been balanced for you. Let’s see if you can balance one on your own.

___Na + ___H 2 O  ___NaOH + ___H 2 This is the reaction for sodium metal with water. How can you balance this reaction?

Now I will provide an equation that is balanced, but is missing the product’s formula. Can you predict the product of this reaction? C 6 H 12 O O 2  6 CO _______

Predict the product Given the reactants, predict the product in these reactions. 2 Fe + Cl 2  _________ 2 P + 2 O 2  __________ Ca + S  _________ 2 C + 2 H 2  __________ Are these products ionic or covalent? Can you draw out the product on the fourth example?

Sodium hydroxide (NaOH) is a potent base that draws water and carbon dioxide out of the air if left in the open. It is also a base used to neutralize certain acids. ___ NaOH + ___ CO 2  ___ Na 2 CO 3 + ___ H 2 O ___ NaOH + ___ HCl  ___ NaCl + ___ H 2 O

Indiana is well known for its limestone, harvested around Bloomington. Limestone is a hard deposit (mostly calcium carbonate) that was likely deposited by marine life. Limestone is used in building, but has stopped being used for monuments in densely-populated areas. Humans have a large impact on the environment, with waste producing phenomena like smog and acid rain.

A reaction for dissolving calcium carbonate is: ___CaCO 3 + ___HCl  ___H 2 O + ___CO 2 + ___CaCl 2 Why might limestone be a poor building material choice for densely-populated cities like Los Angeles or New York City? Acid rain eats away at the faces of limestone buildings, eroding the strength of the building. FYI - The product, calcium chloride (CaCl 2 ), is used as salt for roads (rock salt) and water hardeners.

Individual/Small group Practice Practice with a partner or individually on balancing some chemical equations. For each of the problems, find ALL of the coefficients to balance the equation. – Aim for 10 basic and % – For extra practice, go for the mastery problems – I know they won’t all fit on the worksheet. Just fill in the first 13, then work on scrap paper. – Write down your problems on the worksheet and turn it in at the end of class.

Basic problems CH 4 + O 2  CO 2 + H 2 OKClO 3 → KCl + O 2 H 2 + O 2 → H 2 OP 4 + O 2 → P 2 O 5 Al + Br 2 → AlBr 3 CCl 4 +O 2  CO 2 +Cl 2 C 3 H 8 + O 2  CO 2 + H 2 OSnO 2 + H 2 → Sn + H 2 O C 6 H 6 + O 2 → CO 2 + H 2 OAgI + Na 2 S → Ag 2 S + NaI Advanced problems Na + C 2 Cl 6 → NaCl + C 2 Cl 2 C 2 H 6 + O 2  CO 2 + H 2 O C 2 H 3 Br 3 +O 2  CO 2 +HBrP 4 + HCl + O 2 → PCl 3 + H 2 O AlBr 3 + Cl 2 → AlCl 3 + Br 2 C 6 H 5 F+O 2  CO 2 +H 2 O+F 2 CaCN 2 +H 2 O  CaCO 3 +NH 3 TiCl 4 + H 2 O → TiO 2 + HCl C 6 O 6 Cr + Cl 2 → CrCl 3 + CO Mastery problems AlI 3 + HgCl 2 → AlCl 3 + HgI 2 HSiCl 3 + H 2 O  H 10 Si 10 O 15 + HCl KOH + H 3 PO 4 → K 3 PO 4 + H 2 OBa 3 N 2 + H 2 O → Ba(OH) 2 + NH 3 Ca(OH) 2 + H 3 PO 4 → Ca 3 (PO 4 ) 2 + H 2 ONH 3 + CO → CH 4 + N 2 + O 2 AgNO 3 + K 3 PO 4 → Ag 3 PO 4 + KNO 3 C 7 H 9 + HNO 3  C 7 H 6 (NO 2 ) 3 + H 2 O