Word Equations for Chemical Reactions Tutorial

Key Concepts

• In a chemical reaction substances react to produce new substances.
• The substances we start with are called reactants.

  Reactants can be elements or compounds.

• The new substances that are produced are called products.

  Products can be elements or compounds.

• A word equation is a short-hand way of describing a chemical reaction.

  reactant(s) → product(s)

• A word equation shows the names of the reactants on the left hand side.

  If more than one reactant is present then the names of each reactant are separated by a plus sign (+).

• An arrow is used to show the direction of the reaction: →
• A word equation shows the names of the products on the right hand side of the arrow.

  If more than one product is present then the names of each product are separated by a plus sign (+).

• Sometimes the conditions required for the chemical reaction to take place, such as heat or light, will be written above the arrow.

  reactants

  heat →

  products

• The general form of a word equation is shown below:

  	reactants			→	products
  General word equation:	reactant A	+	reactant B	→	product C	+	product D

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Identifying Reactants and Products in Chemical Reactions

Reactants are the substances we start with.

Products are the new substances that are formed as a result of the chemical reaction between the reactants.

Reactants and products can be elements or compounds.

An element has a name that is just one word. You can find the names of elements in the periodic table of the elements.
The names of lots of metal elements end in "ium", for example sodium, calcium, magnesium, aluminium (NOTE that helium is an exception because it is an element but it is a non-metal!).
But the names of some metals do not end in "ium", for example, iron, silver, gold, copper, zinc, lead, mercury, nickel.
The names of some non-metal elements end in "ine", for example, fluorine, chlorine, bromine, iodine.
The names of other non-metals end in "en", for example, hydrogen, oxygen, nitrogen.
The names of some non-metal elements end in "on", for example, carbon, neon, argon, krypton, radon.
Phosphorus and sulfur are also elements that are non-metals.

In general the name of a compound will be made up of two words.
There are lots of exceptions! For example, water is a compound, ammonia is a compound, ethanol is a compound. However, you will not find these names on the periodic table of the elements so these are NOT elements, we infer that they must be compounds.
To identify whether you are looking at the name of two elements or the name of a compound we can take clues from English grammar.
If I want to list elements I separate two names with "and", for example, sodium and oxygen.
But, if I am referring to the name of a compound, then the "and" will be missing, for example, sodium oxide is the name of a compound.
If I want to separate the names of more than two elements I use a comma, for example, hydrogen, carbon and oxygen (a list of 3 elements).
But hydrogencarbonate (one word), or hydrogen carbonate (two words but no and between them), is the name of a compound.

Let's see if we can identify the names of reactants (the substances we start with) in the following description of a chemical reaction:

When a piece of zinc is placed in a beaker containing hydrochloric acid, bubbles of hydrogen form on the surface of the metal.

For this chemical reaction we have two substances to start with, that is, we have two reactants. The two reactants are:

• zinc
  (the name of an element that is a metal, you will find this name on the periodic table)
• hydrochloric acid
  (the name of a compound, we have two words with no "and" between them, and you will not find this name on the periodic table).

Let's see if we can identify a new substance that has been produced, that is, let's find the name of a product of this chemical reaction:

When a piece of zinc is placed in a beaker containing hydrochloric acid, bubbles of hydrogen form on the surface of the metal.

Hydrogen is a product, it is the new substance formed when we mix the reactants (zinc and hydrochloric acid) together.
Hydrogen was NOT present at the start, it was produced as a result of the chemical reaction.

Consider the description below for preparing barium sulfate, a white solid that is used in medicine (known as a "barium meal"):

Barium sulfate can be prepared by adding sulfuric acid to a solution of barium nitrate.

What are the reactants in this chemical reaction?
The reactants are the substances that we start with which are the sulfuric acid which we add to the barium nitrate, so there are two reactants; sulfuric acid and barium nitrate.

What is the product of this chemical reaction?
The product is the new substance that is produced (or made, or formed, or prepared).
The information tells us how to prepare barium sulfate, that is, this chemical reaction will make (or produce) barium sulfate, therefore the product of the chemical reaction is barium sulfate.

Writing Word Equations for Chemical Reactions

Chemical reactions are occuring all around you every day and every night.

For lunch I had a sandwich. The bread in the sandwich contains starch. When I eat starch, a chemical reaction takes place in my mouth which breaks that starch down into sugars. As I continue to chew my sandwich I can taste the sweetness of these sugars as they are produced.

If I want to write a word equation to represent this chemical reaction, the first thing I need to do is identify the names of the reactants and products.
The reactant is the substance we start with, the substance that is present before the chemical reaction starts.
The reactant in my bread is the starch.
The product of a reaction is the substance that is formed, or produced, as a result of the chemical reaction taking place.
The product of the chemical reaction when I eat starch are the sugars that are formed.

A word equation shows the reactant reacting to produce the product:

reactant → product

The arrow in the general form of the equation above shows the direction in which the chemical reaction proceeds:
that is, we start with "reactant" and we end up with "product".

In order to write a word equation to represent a chemical reaction I must:

• write the name of the reactant (starch)
• draw an arrow to show the direction of the chemical reaction, →
• write the name of the product (sugars) to the right of the arrow

So my word equation for the breakdown of starch into sugars in my mouth is:

A reactant could break down to produce more than one new substance, that is, more than one product.

Today I drank a can of cola with my sandwich for lunch. Cola is a fizzy drink (or soda) and it is fizzy because bubbles of carbon dioxide gas are continually being produced. These bubbles force their way up through your drink until they reach the surface where they can finally escape and join the atmosphere. This carbon dioxide gas is produced when the carbonic acid in the drink decomposes (breaks down). The other product of this chemical reaction is water.

I want to write a word equation to describe the chemical reaction in which carbonic acid decomposes to produce carbon dioxide and water:

reactant → products

In order to write a word equation to represent a chemical reaction I must:

• write the name of the reactant (carbonic acid)
• draw an arrow to show the direction of the chemical reaction, →
• write the names of each of the products separated by a plus sign (+) to the right of the arrow (carbon dioxide + water)

So my word equation for the decomposition of carbonic acid in my cola drink is:

There may be more than one reactant present in a chemical reaction.

It was only after finishing my lunch and experiencing the discomfort of indigestion that I remembered why I never drink fizzy drinks. Indigestion is caused by an increase in the acid level of my stomach. The stomach contains an acid known as hydrochloric acid. I can neutralise some of the excess hydrochloric acid by taking an indigestion tablet. My indigestion tablets contain a substance known as calcium carbonate. The calcium carbonate reacts with some of the hydrochloric acid to produce calcium chloride, water and carbon dioxide gas. The carbon dioxide gas is released in the form of a satisfying burp which makes you feel much better!

I want to write a word equation to describe the chemical reaction in which hydrochloric acid reacts with calcium carbonate to produce calcium chloride, carbon dioxide and water:

reactants → products

In order to write a word equation to represent a chemical reaction I must:

• write the names of each of the reactants separated by a plus sign (+) (hydrochloric acid + calcium carbonate)
• draw an arrow to show the direction of the chemical reaction, →
• write the names of each of the products separated by a plus sign (+) to the right of the arrow (calcium chloride + carbon dioxide + water)

So my word equation for the reaction occurring between hydrochloric acid and calcium carbonate is:

De-coding a Word Equation

A word equation is a quick, short-hand way of telling us the name of the reactant(s) we need to use for the chemical reaction, and the names of the new substance(s), the product(s), that will be produced as a result of the chemical reaction.

If we see a word equation written down, we can follow the directions it gives in order to make the make new substance(s).

For example, consider the word equation given below:

magnesium + oxygen → magnesium oxide

This chemical equation tells us that if we expose magnesium (a shiny metal) to oxygen (a colourless gas in the atmosphere), a new substance called magnesium oxide will be produced (which is a grey-white solid).

Here is another example of a word equation:

hydrochloric acid + iron → iron chloride + hydrogen

This chemical equation tells us that if we add hydrochloric acid to iron (a metal) in a beaker in the lab, then they will react to produce two new substances; iron chloride and hydrogen (which is a colourless gas that easily burns).
Equally it tells us that if we were to eat some iron then when that iron reaches our stomach which contains hydrochloric acid, a chemical reaction would occur in which iron chloride and hydrogen would be produced. The hydrogen gas would be released as a burp!
If I add hydrochloric acid to iron, I produce iron chloride and hydrogen.
If I add iron to hydrochloric acid, I produce iron chloride and hydrogen.

The order in which we list the reactants does not matter. But reactants MUST be written to the left of the arrow (→).
The order in which we list the products does not matter. But products MUST be written to the right of the arrow (→).

The chemical reaction between iron and hydrochloric acid to produce iron chloride and hydrogen can be written in any of the following ways because they all represent the same chemical reaction:

hydrochloric acid + iron → iron chloride + hydrogen

iron + hydrochloric acid → iron chloride + hydrogen

iron + hydrochloric acid → hydrogen + iron chloride

hydrochloric acid + iron→ hydrogen + iron chloride

Problem Solving

The Solution to the Problem

(using the StoPGoPS approach to problem solving)