## Chem – Predicting Types of Chemical Equations Part 1

What sections should I know before attempting to learn this section?

IF YOU DO NOT FEEL CONFIDENT IN YOUR CHEMISTRY SKILLS SO FAR, I STRONGLY URGE YOU TO REVIEW THE DIFFERENT SECTIONS, LINKED IN BLUE, BELOW THIS TEXT.

2) Ions

How do you predict the products of a chemical equation?

Predicting the products of a chemical equation is one of the most comprehensive and therefore complicated things we have had to do yet.  Mostly, it centers around knowing how to take many concepts that we have learned in previous areas of chemistry and use them together to form one large picture of how the chemical reaction changes the compounds or molecules.  In this section I left off the states of each of matter for each of the chemicals because I did not want that to distract people from understanding more important issues.

What are the most important steps to remember while you are trying to answer the practice problems about predicting chemical equations?

1) Remember to ALWAYS produce the chemical equation’s products BEFORE you try to balance how many of each chemical.

2) Some chemical equation types (mostly synthesis and decomposition) can have multiple different right answers for their products.  Where that is possible I give only one right answer although more are possible.  However, on single replacement, double replacement, and combustion the problems I picked have only one right answer and all those you encounter in your class should have only one right answer.

Examples: If you have the reactants of a chemical equation and know what type of chemical equation it is then give the products of the chemical equation.

Single Replacement:

Na + MgBr2 ——> ?

Answer: 2 Na + MgBr2 ——> Mg + 2 NaBr

Synthesis:

Ca + C4 + O2 ——> ?

Answer: 4 Ca + C4 + 6 O2 ——> 4 CaCO3

VIDEO Predicting Chemical Equations Demonstrated Example 1: If you have the reactants of a chemical equation and know what type of chemical equation it is then give the products of the chemical equation.

Single Replacement:

Li + Ba(NO3)2 ——> ?

Step 1:

Where do I start?

Answer: Look at the possible charges of each element according to the ions of the periodic table.

Li = +1, Ba = +2, NO3 = -1

Step 2:

How do I use the charges?

Both Li and Ba are positive charges so they will swap.

Step 3:

What is the compound made up of Li and NO3?

 Li+ NO3– Total = +1 -1

Step 4:

What will Ba look like?

Answer: Since Ba is not a part of the diatomic molecules it will be single and alone: Ba

Step 5:

What does my answer look like so far?

Answer: Li + Ba(NO3)2 ——> Ba + LiNO3

Step 6:

How do I balance the equation?

COMPLETE ANSWER: 2 Li + Ba(NO3)2 ——> Ba + 2 LiNO3

VIDEO Predicting Chemical Equations Demonstrated Example 2: If you have the reactants of a chemical equation and know what type of chemical equation it is then give the products of the chemical equation.

Double Replacement:

MgO + KF ——> ?

Step 1:

Where do I start?

Answer: Look at the possible charges of each element according to the ions of the periodic table.

Mg = +2, O = -2, K = +1, F = -1

Step 2:

How do I use the charges?

Answer: The positive charges of Mg and K will swap places with their negative partners.

Step 3:

What is the compound made up of Mg and F?

 Mg2+ F– F– Total = +2 -2

Step 4:

What is the compound made up of K and O?

 K+ O2- K+ Total = +2 -2

Step 5:

What does my answer look like so far?

Answer: MgO + KF ——> MgF2 + K2O

Step 6:

How do I balance the equation?

COMPLETE ANSWER: MgO + 2 KF ——> MgF2 + K2O

VIDEO Predicting Chemical Equations Demonstrated Example 3: If you have the reactants of a chemical equation and know what type of chemical equation it is then give the products of the chemical equation.

Single Replacement:

P + Fe2O3 ——> ?

Step 1:

Where do I start?

Answer: Look at the possible charges of each element according to the ions of the periodic table.

We have to break down the Fe and O compound to get the charge on Fe.

P = -3, Fe = +3, O = -2

 Fe3+ O2- Fe3+ O2- O2- Total = +6 -6

Step 2:

How do I use the charges?

Both P and O are negative charges so they will swap.

Step 3:

What is the compound made up of Fe and P?

 Fe3+ P3- Total = +3 -3

Step 4:

What will O look like?

Answer: Since O is a part of the diatomic molecules it will be paired with itself: O2

Step 5:

What does my answer look like so far?

Answer: P + Fe2O3 ——> FeP + O2

Step 6:

How do I balance the equation?

COMPLETE ANSWER:4 P + 2 Fe2O3 ——> 4 FeP + 3 O2

VIDEO Predicting Chemical Equations Demonstrated Example 4: If you have the reactants of a chemical equation and know what type of chemical equation it is then give the products of the chemical equation.

Double Replacement:

PbS2 + AlPO4 ——> ?

Step 1:

Where do I start?

Answer: Look at the possible charges of each element according to the ions of the periodic table.

We have to break down the Pb and S compound to get the charge on Pb.

Answer: Pb = +4, S = -2, Al = +3, PO4 = -3

 Pb4+ S2- S2- Total = +4 -4

Step 2:

How do I use the charges?

Answer: The positive charges of Pb and Al will swap places with their negative partners.

Step 3:

What is the compound made up of Pb and PO4?

 Pb4+ PO43- Pb4+ PO43- Pb4+ PO43- PO43- Total = +12 -12

Step 4:

What is the compound made up of Al and S?

 Al3+ S2- Al3+ S2- S2- Total = +6 -6

Step 5:

What does my answer look like so far?

Answer: PbS2 + AlPO4 ——> Al2S3 + Pb3(PO4)4

Step 6:

How do I balance the equation?

COMPLETE ANSWER: 3 PbS2 + 4 AlPO4 ——> 2 Al2S3 + Pb3(PO4)4

VIDEO Predicting Chemical Equations Demonstrated Example 5: If you have the reactants of a chemical equation and know what type of chemical equation it is then give the products of the chemical equation.

Combustion:

C2H6 + O2 ——> ?

Step 1:

Where do I start?

Answer: The products of a combustion equation are always CO2 and H2O?

Step 2:

What does my answer look like so far?

Answer: C2H6 + O2 ——> CO2 + H2O

Step 3:

How do I balance the equation?

COMPLETE ANSWER: 2 C2H6 + 7 O2 ——> 4 CO2 + 6 H2O

VIDEO Predicting Chemical Equations Demonstrated Example 6: If you have the reactants of a chemical equation and know what type of chemical equation it is then give the products of the chemical equation.

Synthesis:

NH4+ + SO42- ——> ?

Step 1:

Where do I start?

Answer: Bring the two reactant compounds together into a single product compound. In this case bring the two ions together.

Step 2:

What is the compound that contains the two ions?

 NH4+ SO42- NH4+ Total = +2 -2

Step 3:

What does my answer look like so far?

NH4+ + SO42- ——> (NH4)2SO4

Step 4:

How do I balance the equation?

COMPLETE ANSWER: 2 NH4+ + SO42- ——> (NH4)2SO4

VIDEO Predicting Chemical Equations Demonstrated Example 7: If you have the reactants of a chemical equation and know what type of chemical equation it is then give the products of the chemical equation.

Decomposition:

N2O3 ——> ?

Step 1:

Where do I start?

Answer: Break up the one reactant into many products. It can be two or more. I simply broke the reactant compound into its elements (remember N and O are diatomic).

N2O3 ——> N2 + O2

Step 2:

How do I balance the equation?

COMPLETE ANSWER: 2 N2O3(g) <——> 2 N2(g) + 3 O2(g)

PRACTICE PROBLEMS: Give the balanced complete reaction below.

 Synthesis Mg + O2 —> ? 2 Mg + O2 —> 2 MgO Decomposition AlBr3 —> ? 2 AlBr3 —> 2 Al + 3 Br2 Combustion C6H12O6 + O2 —> ? C6H12O6 + 6 O2 —> 6 CO2 + 6 H2O Double Replacement Ca(OH)2 + Na2S —> ? Ca(OH)2 + Na2S —> CaS + 2 NaOH Single Replacement Li + Ba3P2 —> ? 6 Li + Ba3P2 —> 3 Ba + 2 Li3P Combustion C4H10 + O2 —> ? 2 C4H10 + 13 O2 —> 8 CO2 + 10 H2O Double Replacement MnCO3 + K3PO4 —> ? 3 MnCO3 + 2 K3PO4 —> Mn3(PO4)2 + 3 K2CO3 Single Replacement F2 + NH4Br —> ? F2 + 2 NH4Br —> 2 NH4F + Br2  