Predicting Reactions: A System

General Chemistry Index

Where are we going with this? This page will assist in developing the ability to predict products of simple reactions as listed in of reactions: synthesis (i.e., combination), decomposition, single displacement, double displacement, acid/base, and combustion.

Predicting Reactions: A System 
What happens if I mix this with that?

Predicting products of chemical reactions is a process by which potential reactants are scrutinized to determine if they will react and if so what product(s) will be formed.

What happens if I mix this baking soda with vinegar?
What happens if I let this spilled gasoline sit on the painted garage floor?
What happens if I pour bleach directly onto my clothes?

Predicting chemical reactions does not only take place in the lab, but actually is a part of everyday life! However, in the lab, we can be more specific and isolate the this and the that more.

So… I told you this would be long! Maybe another soda or cup of coffee?

Recall: the goal is to end up with neutral molecules no matter what you have to do to the subscripts on the PRODUCT side.

Let's just say we are starting with "real" molecules on the reactant side, to begin with, okay? Coming up with a system to predict the products is, at best, a starting place. 

Because of the vast scope of chemistry, there will be variations that this system will not cover (probably). And, there are always exceptions!

Back to the original question, but flipping it: If I mix this with that, what happens?

The system I'm going to offer expands on that question thusly:

What do you have to start with?

This step identifies what kind of reaction you could be looking at. Is it synthesis? Decomposition? Etc. 

 

What does it become? 

1. Will it even react? 
2. What combination of atoms are needed in the product such that the compound molecule is neutrally charged? (AKA what are the subscripts?) 
3. What is the FINAL balanced equation?

 

So, here is a "decision tree" for what to do to predict the products of a chemical reaction. 

Predicting the Products of Chemical Reactions Decision Tree

What do you have to start with?

• Two elements: goto Synthesis Reaction below (Click) 

• One compound: goto Decomposition Reaction below (Click)

• An element and a compound: goto Single Displacement Reaction below (Click) 

• Two compounds: goto Double Displacement Reaction below (Click) 

What does it become?

Synthesis Reaction (background)

 

First off, will they react? 

For two elements to react, they need to have opposite valence charges (one plus, one minus = one has four or less electrons in its valence orbitals, one has four or more)

Secondly, if they will react, how many of each are needed to get a neutrally charged compound molecule in the product?

The subscripts denote how many of each thing will be present in the neutrally charged molecule. You can "criss-cross" the charges of two elements (then reduce mathematically) to find the right numbers.

For instance, take carbon and oxygen.

Oxygen has a valence of -2.

Carbon has a charge of ±4. (Since oxygen is negative, we'll use the +4)

C + O2 --> ??

So, it has to be C?O?

Criss-cross the charges:  C2O4 

Reduce the subscripts mathematically: C2O4   becomes  CO2

C + O2 --> CO2

Thirdly, balance the equation such that the same number of each type of atom is present on both sides:

C + O2 --> CO2 (was already in balance)

______________________________

Decomposition Reaction (background)

 

First off, will they react? 

Not everything will break apart easily. Somethings only break apart at high temperatures.

It seems fair to presume that, if given a predicting products exercise, the compound will, by some means react and decompose into the parts.

Secondly, if… Well, this one is pretty easy. Whatever you start with breaks apart. But… into how many pieces! (Probably two.) Usually, it will look like this:

AB --> A + B 

Both the A and the B have to be neutral molecules or elements. And don't forget about those diatomic elements! 

Thirdly, balance the equation such that the same number of each type of atom is present on both sides:

2H2O → 2 H2 + O2

It could be tricky, though!

Na2CO3 → Na2O + CO2

______________________________

Single Displacement Reaction (background)

First off, will they react? 

For one thing to replace another… Let's say it like this… For A to replace B, 

A + BC --> ?? + ????

A has to be more highly reactive than B. How would anyone know that? There is a chart!

So, sodium won't replace potassium. Etc.!

 

Also, either B or C could be a polyatomic ion! That makes it harder to figure out what is being replaced. Look into the BC part and match one of them to the A with regards to location on the periodic table. There's a good chance that A will be in a family/group that is near the family or group of B or C. (You'll have to be openminded about this claim when dealing with transition elements.)

 

Secondly, if they will react, how many of each are needed to get a neutrally charged compound in the product?

You know what you are starting with, so the reactant side is done. Let's do aluminum and HCl as an example…

Al + HCl --> ?? + ?

Since Al will, in fact, replace H, the product side will be:

Al + HCl --> AlCl + H

Product side subscript time:

This should be fun!

1. H is diatomic, so it will be H2

2. The AlCl has to become neutrally charged. 

The subscripts denote how many of each thing will be present in the neutrally charged molecule. You can "criss-cross" the charges of two elements (then reduce mathematically) to find the right numbers.

For instance, take carbon and oxygen.

Al has a valence of +3.

Cl has a charge of -1.

The balanced molecule will be AlCl3

Thirdly, balance the equation such that the same number of each type of atom is present on both sides:

2Al + 6HCl --> 2AlCl3 + 3H2

______________________________

Double Displacement Reaction (background)

First off, will they react? 

For one thing to replace another… Let's say it like this… For A to replace B, 

AB + CD --> ???? + ????

Deciding what is A and what is B can be hard when polyatomic ions are involved. Really, the only way to get good at this is to do it a lot.

Look at A and C first. Are they both metals? Hmmm… What about B and D? Both polyatomic ions? If so, do they both have a positive or negative charge (There is a chart!)? If both B and D are negative and both A and C are positive (which is kinda the normal way of writing molecules) then you can find your potential "swaps."

At this point, you have to answer the question! Will they react?

Answering this question is complex, since the reactivity of each of the four parts is in play. How is it done? (CLICK HERE)

So… 

1. Does it form water? 

2. Does it form a gas? 

3. And then that insolubility thing… easy! 

Secondly, if they will react, how many of each part is needed to get a neutrally charged compound in the product?

The work done in the first step should have resulted in you knowing what the AB and CD parts are.  The product will become AD and BC

You know what you are starting with, so the reactant side is done. Let's do the follow as an example…

Fe2(SO4)3 + KOH → 

So, there's some AB and CD up there? That looks like a sentence in a foreign language!

So this… 

 

AB          +   CD  → AD + CB

Fe2(SO4)3 + KOH →

(When you predict the swapped product, put in the parentheses to start with, at least in your head.)

Fe2(SO4)3 + K(OH)1 →

Fe2(SO4)3 + K(OH)1 → Fe?(OH)? + K?(SO4)?

Product side subscript time:

This should be… never mind!

1. Do that thing with the charges to get balanced molecules. For instance…

K (from periodic table) has a charge of + 1

SO4 has a charge of -2

Criss-cross the charges to get K2(SO4)1

Chemistry "grammar" says we don't write ones and if the subscript is one don't use parentheses.

Thus, we get:

K2SO4 

Using the the example from above, working through the process of getting both products to a neutral charge, we get the unbalanced (but each part is a neutrally charged molecule) equation:

?Fe2(SO4)3 + ?KOH → ?K2SO4 + ?Fe(OH)3

Thirdly, balance the equation such that the same number of each type of atom is present on both sides.

So for the above example…

Fe2(SO4)3 + 6KOH → 3K2SO4 + 2Fe(OH)3

 

Predicting Reactions: Overview

General Chemistry Index

Where are we going with this? This page will assist in developing the ability to predict products of simple reactions as listed in of reactions: synthesis (i.e., combination), decomposition, single displacement, double displacement, acid/base, and combustion.

Predicting Reactions: Overview 
What happens if I mix this with that?

This comes up every week. Someone asks me what happens if I mix two things together. Or they ask what happens if the eat/drink/swallow something.

The answer to that question is the very heart of predicting the products of a chemical reaction. Predicting products of chemical reactions is a process by which potential reactants are scrutinized to determine if they will react and if so what product(s) will be formed.

What happens if I mix this baking soda with vinegar?
What happens if I let this spilled gasoline sit on the painted garage floor?
What happens if I pour bleach directly onto my clothes?

Predicting chemical reactions does not only take place in the lab, but actually is a part of everyday life! However, in the lab, we can be more specific and isolate the this and the that more.

So… here we go! This is going to be long, so get comfy. Maybe a soda or cup of coffee?

So, a very quick review of chemical reactions… 

• You start off with some reactants.
• Something happens.
• There are some products.
  
  
• Reactions are dictated by the law of conservation of matter such that…

• The number of and type of atoms on the reactant side is equal to the number of and type of atoms on the product side.
• The total mass on the reactant side is equal to the total mass on the product side (ignoring mass/energy E=mc² stuff)

• Compounds form in fixed, specific ratios of atoms. 

Okay, back to that what happens stuff…

You have a couple of reactants. You want to know what happens if they combine (assuming they will). If they DO combine, then a few things need to be considered.

The compound formed must end up with a neutral charge. That goes back to all those bonding types and such. So, at a simplistic level, you can think of it as they are trying to fill their valence electron orbitals. You are going to rely on the periodic table to provide information about those charges! 

Oh… and those polyatomic ions… A CHART would be nice!

Okay, this is a little shifty, here… About those subscripts… Remember that the subscript gives the number of each atom (or polyatomic ion) in the molecule. Changing the subscripts changes what you have:

H2O is not the same as H2O2. The first is water. The second is peroxide. You die if you don't drink the first. You die if you DO drink the second.

So, you have two things on the table. You know what they are. (The bottle is labeled!) So, you KNOW the formula for those molecules. You CANNOT change the subscripts of the things on the reactant side.

When they react (if the react), they are going form NEW things. (Pretty much the definition of a chemical reaction.) So, the NEW things have their own formulas—new formulas with their own symbols and subscripts. Hence, the subscripts from the reactant side do NOT carry through to the product side.

Look at a couple of balanced reactions as an example:

2H2 + O2 → 2H2O

6CO2 + 6H2O → C6H12O6 + 6O2

SiCl4 + 6H2O → H4SiO4 + 6HCl

2Al + 6HCl → 2AlCl3 + 3H2

Na2CO3 + 2HCl → 2NaCl + H2O + CO2

So… 

End up with neutral molecules no matter what you have to do to the subscripts on the PRODUCT side.

Now, just how do we do that?

The actual process of predicting the products of a chemical reaction is to look at what you have and find ways of rearranging it into new substances. Arguably, it is "one of those things" you grow into, perhaps as much "just getting it" as it is having a rubric to do so. 

BUT! We shall try to come up with a system to predict products of a chemical reaction, all the same!

Ions and Their Charges

General Chemistry Index

Where are we going with this? This page will assist in developing the ability to describe, classify, and give examples of various kinds of reactions: synthesis (i.e., combination), decomposition, single displacement, double displacement, acid/base, and combustion.

Ions and Their Charges

Metals in compounds will usually give electrons to nonmetals or polyatomic ions with a negative charge. Some metals will give different numbers of electrons depending on the other part of the reaction. 

Parts of a compound that give their electrons away are considered positive ions or cations. The parts of a compound that receive the electrons are negative ions or anions. 

Compounds will form in such a way that the net charge is zero. The valence number on the periodic table will reflect the charges of the elements.

Numerous elements will combine into polyatomic "chunks" and, as such, act like a single thing in a reaction. Listed below are some common (and not so common) polyatomic "chunks."

Polyatomic Ions

The following Google Sheet can be sorted… 

Also, you can "command-F" after clicking one of the cells and search it.

More

Other Ions

In many reactions, the group in which an element is located will provide its charge. The table below is a handy reference.

Common Charges from Periodic Table Column / Family / Group
1	2	3-12	13	14	15	16	17	18
+1	+2	varies	+3	±4	-3	-2	-1	0

The following SORTABLE table presents the elements and their charges in list format.

Various Elements and Their Charges

The following Google Sheet can be sorted… 

Also, you can "command-F" after clicking one of the cells and search it.

Diatomic Elements

These elements bond to themselves in order to be more stable.

Hydrogen H2

Nitrogen N2

Oxygen O2

Fluorine F2

Chlorine Cl2

Bromine Br2

Iodine I2

SORTING THE TABLES:

Note: Sorting functionality is limited due to Google implementation of "sharing view only" functions.
 

Activity Series

General Chemistry Index

Where are we going with this? This page will assist in developing the ability to describe, classify, and give examples of various kinds of reactions: synthesis (i.e., combination), decomposition, single displacement, double displacement, acid/base, and combustion.

Activity Series

One chemical property is reactivity. Not all things are equally reactive. Reactivity relates to how vigorously something will react with other things.

There's another characteristic of matter related to how likely something is to react. In an imaginary way, you could think that if you throw some (let's say fluorine) into a bucket and then toss two other things in, which one will react? Whichever one will react is higher on the activity series. While the activity series relates electronegativity, it is not a perfect correlation for the metals.

So, given two different elements, which one is more apt to react? Depending on how readily something will react, we can produce a ranked list.

Activity Series: The reactivity series is a list of metals ranked in order of decreasing order of relative tendency to react. (More)

The following list indicates a simple version of an activity series chart. Elements cannot replace anything ABOVE them in the list below. If such is attempted, there will be no reaction.

The reactivity series follows the order, from most reactive to least reactive:

Metals

Most active or most easily oxidized 

Lithium              Li( s ) → Li 1+ ( aq )  + e – 

Rubidium                Rb  → Rb 1+   +  e –

Potassium         K( s ) → K 1+ ( aq )   + e –

Barium                 Ba( s ) → Ba 2+ ( aq )   + 2e – 

Strontium                Sr

Calcium                 Ca( s ) → Ca 2+ ( aq )  + 2e –

Sodium                 Na( s ) → Na + ( aq )   + e –

Magnesium              Mg( s ) → Mg 2+ ( aq )   + 2e –

Aluminum         Al( s ) → Al 3+ ( aq )   + 3e –

Manganese         Mn (s) → Mn 2+ ( aq )   + 2e –

Zinc                         Zn( s ) → Zn 2+ ( aq )   + 2e –

Chromium         Cr( s ) → Cr 3+ ( aq )   + 3e 

Iron                         Fe( s ) → Fe 2+ ( aq )   + 2e –

Cadmium                 Cd

Cobalt                 Co( s ) → Co 2+ ( aq )   + 2e –  

Nickel                 Ni( s ) → Ni 2+ ( aq )   + 2e –

Tin                         Sn( s ) → Sn 2+ ( aq )   + 2e –

Lead                 Pb( s ) → Pb 2+ ( aq )   + 2e –

Hydrogen         H2 ( g ) → 2H + ( aq )   + 2e –

Antimony                Sb

Arsenic                 As

 

Bismuth                 Bi

Copper                 Cu( s ) → Cu 2+ ( aq )   + 2e –

Tungsten                 W  

*Mercury                 Hg( l ) → Hg 2+ ( aq )   + 2e –            *Some sources swap Hg and Ag (e.g. this)

*Silver                Ag( s ) → Ag + ( aq )   + e –

Palladium               Pd

Platinum                 Pt( s ) → Pt 2+ ( aq )   + 2e –

Gold                 Au( s ) → Au 3+ ( aq )   + 3e –

Least active or most difficult to oxidize

Non-Metals 

Non-metals tend to follow electronegativity with regard to if they will replace another element.

(Most electronegative to least)

Name                        Electronegativity

Fluorine F                             3.98
Chlorine Cl                           3.16

Oxygen O                             3.44
Nitrogen N                            3.04

Bromine Br                           2.96
Iodine I                                 2.66

Sulphur S                              2.58

Selenium Se                          2.55

Carbon C                               2.55
Phosphorus P                        2.19

______________

A few sources…

https://www.thoughtco.com/activity-series-of-metals-603960

https://courses.lumenlearning.com/cheminter/chapter/chart-activity-series-of-metals/

https://www.sd308.org/cms/lib/IL01906463/Centricity/Domain/2189/Activity%20Series%20Chart.pdf

http://foradorimath.weebly.com/uploads/4/6/3/5/4635110/2a_-_activity_series.pdf

https://en.wikipedia.org/wiki/Reactivity_series#Table

https://www.templateroller.com/template/585124/activity-series-metals-and-non-metals-cheat-sheet.html

Comments:

There seems to be, in various sources, some different rankings, frequently putting Lithium further down the list. 

Types of Reactions—Decomposition

 General Chemistry Index

Where are we going with this? This page will assist in developing the ability to describe, classify, and give examples of various kinds of reactions: synthesis (i.e., combination), decomposition, single displacement, double displacement, acid/base, and combustion.

Activity: Types of Reactions—Decomposition

(Thermal Decomposition of Sodium Bicarbonate)

Background Information: Types of Reactions

The purpose of this activity is to provide hands-on experience using laboratory techniques to observe a decomposition reaction. 

Evidence of the reaction is easily seen in the production of gas.

Primary Reaction: 2 NaHCO3 → Na2CO3 + H2O + CO2

Possible Secondary Reaction: Na2CO3 → Na2O + CO2

The decomposition of anhydrous sodium carbonate into sodium oxide and carbon dioxide occurs slowly at room temperature and proceeds to completion at 851 C. 

Link to activity worksheet:  CLICK HERE

The video below demonstrates how to set up the lab and collect the data. Actual data collected from the video may be used to do the lab virtually.

https://youtu.be/0ivlExWDkdA

Activity: Types of Reactions—Synthesis (Burning Iron)

General Chemistry Index

Where are we going with this? This page will assist in developing the ability to describe, classify, and give examples of various kinds of reactions: synthesis (i.e., combination), decomposition, single displacement, double displacement, acid/base, and combustion.

Activity: Types of Reactions—Synthesis (Burning Iron)

Background Information: Types of Reactions

The purpose of this activity is to provide hands-on experience using laboratory techniques to observe a synthesis reaction. Because the reaction includes oxygen and energy is given off in the form of heat and light, it is also arguably an example of combustion.

Evidence of the reaction is easily seen in a color change of the steel wool.

Additionally, for more advanced students, the discussion of the procedures highlights errors in procedure and techniques.

The reaction that will be performed is a synthesis reaction combining iron and oxygen:

4Fe + 3O2 →  2Fe2O3

The iron is located in steel wool and the oxygen is provided by the earth atmosphere. The reaction is induced by introducing heat, then it continues producing more heat and light.

Link to activity worksheet:  CLICK HERE

The video below has three parts:

• Setup and Procedures
• Result
• Discussion

https://youtu.be/bP9SzFO1IgQ

Grams to Grams Stoichiometry (Overview)

General Chemistry Index

Where are we going with this? This page will give the ability to demonstrate an understanding of the law of conservation of mass through the use of particle diagrams and mathematical models.

Grams to Grams Stoichiometry
Here, we put it all together!

Suppose you have eleven grams of something. If you combine it with something else, how many grams of the other thing do you need and how many grams will be produced of the whatever…

Wow! That escalated really fast!

Grams to grams stoichiometry is kind of the culmination of the laws of conservation as it relates to chemical reactions. To be so important, it seems like it should be harder!

How Does This Thing Work?

A'ght, let's break this down.

You have some mass of something.

You need find out the mass of that other thing (or things). Or you need to find the mass of the thing that will be produced (because no one sells things by the mole. Now that I said that, someone will probably contradict me with some obscure example!).

What do you do?

First off, you gotta have a balanced equation. 

Next, you gotta convert the mass you have (or weight, if things are awful) in to moles (by using the molecular weights.

Then, you are going to use the number of moles you have to figure out how many moles of the rest of the stuff will be required.

Then, convert the moles you calculated into the masses.

Can we put that into a list?

Balanced chemical reaction 

 

Mass given to moles given. 

See Moles to Grams to Moles

Chemical notation to molecular mass 

 

Moles given to moles needed and produced 

 

Convert from moles needed / produced to masses needed / produced. 

See Moles to Grams to Moles

That makes it look a lot easier! (I always figure I left something out when I make a list like this.)

MORE TO COME!

Chemical Notation to Molecular Mass

General Chemistry Index

Where are we going with this? This page will give the ability to demonstrate an understanding of the law of conservation of mass through the use of particle diagrams and mathematical models.

Chemical Notation to Molecular Mass
This is actually pretty easy. And sort of cool, in a sciency way.

Beginning with the correct notation for a particular element or compound is the first step in doing all this stoichiometry stuff!

The good news is that if you have a balanced chemical reaction, you have the correct notation… you have what you need.

So, we need to figure out how much one mole of a thing is… Good thing we have that periodic table and those atomic masses! 

SEE ALSO, THIS WALKTHROUGH

The atomic weight of an element indicates the mass in grams of one mole of those atoms. Bam!

https://ptable.com/#Properties

So, look at potassium:

The number at the bottom of the element listing is the atomic mass. That number, for potassium, is 39.098.

That means that one mole of potassium has a mass of 39.098 grams. Or if your scale only goes to the .01 accuracy, 39.10 grams.

So, let's go with this and see what happens!

Suppose you have the reaction of K and O2 such that:

4K + O2 --> 2K2O

So, in this step we are answering this question:

What is the mass in grams of each of the molecules in the reaction?

We are NOT asking about total grams. Not in this step. Just the mass of ONE molecule. We are finding the molecular weight. How about a definition?

Molecular weight (analogous to atomic weight) is the mass in grams of one mole of molecules of a substance.

To find molecular weight, add up all of the atomic weights of all the atoms in the molecule.

Let's do that! Could be fun!

In the reaction:

4K + O2 --> 2K2O

we have three molecules (one of which is an element):

K

O2

K2O

https://ptable.com/#Properties

We already looked up K, so we know that one mole of K weighs 39.098 grams.

Now, for that O2. 

Each molecule has two oxygen atoms.

Using the periodic table again, once more looking at the atomic weight, we find that one atom of oxygen has a mass of 15.999 grams.

So, that's the mass of one atom. Now, how many atoms are in each oxygen molecule?

Two (aka 2).

Because it is O2.

So, the mass of the molecule is the mass of the atom times however many atoms there are. Therefore, the mass of one molecule of O2 is found as

15.999 X 2 = 31.998

So, the mass of one molecule of oxygen is 31.998 grams.

Told you it was kinda cool…

Now, we have one more molecule to calculate. The K2O one…

This guy has more than one type of atom in it. But, no biggie. We just add!

K2O

Two K and one O atoms.

So, to be mathy about it, the mass of one K2O is:

K2O[mass]  = 2 • K[mass] + O[mass]

K2O[mass]  = 2 • 39.098 gr + 15.999 gr

K2O[mass]  = 2 • 39.098 gr + 15.999 gr

K2O[mass]  = 94.179 grams

________________________________________________________________

Doing it that way looks awful. How about doing it with the chemical reaction? Could it be worse?

4K + O2 --> 2K2O

First off, we are only looking at the mass of the molecules, so we don't in this case need the coefficients.

So we're going to more or less ignore the coefficients:

4K + O2 --> 2K2O

 

Next, put the atomic masses above each of the atoms. (And spread it out, because you need room.)

39.098            15.999                39.098    |  15.999

4K          +          O2        -->                   2K2O

 

Next, multiply the atomic mass by the subscript in the molecule:

39.098            15.999                39.098      |     15.999

    4K          +        O2           -->                2K2O

39.098            15.999                39.098      |     15.999

       X 1                X 2                    X 2      |         X 1
_______          ______            ________        _____
39.098            31.998                78.196      +     15.999 <--Add the two parts of the molecule.)

                                                                94.195

So, doing that, you now have the molecular weights for each part of the reaction. 

If you have very complex molecules (such as polyatomics), the process is the same. Just more steps.

Molecular Mass of Al(NO2)3
with some rounding.