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Explainer Video

Tutor: Aimee LeBrun

Summary

Chemical equations

In a nutshell

Word and symbol equations can be used to represent the reactions happening between reacting materials and the products that are produced in a reaction.

Word equations

procedure

1.	Work out which two substances are being reacted together.
2.	Write the names of the two reactants with a '+' between them.
3.	Add an arrow, signifying the reaction is taking place.
4.	Finish the equation with the name of the product formed.

Example 1

Write the word equation for the reaction between sodium and chlorine to produce sodium chloride.

The two reacting materials are sodium and chlorine:

$sodium+chlorine$

Add the reaction arrow and finish off with the product substance (sodium chloride):

$sodium+chlorine\rightarrow sodium\,chloride$

Note: Try to write the equation on one line. If this is not possible, write words beneath each other as shown below:

$sodium+chlorine\rightarrow sodium\,\\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,chloride$

Balanced equations

Balanced equations represents substances using formulae. The number of atoms of each element is the same for the reactants and products. The equation must be balanced.

procedure

1.	Work out the formulae for all of the reacting and product materials. Use this to write out the equation.
2.	Count the number of atoms on each side of the equation. If the numbers are unequal the equation needs to be balanced.
3.	To balance the equation, add numbers in front of the substances to make the number of each type of atom equal on either side of the reaction.

Example 2

Balance the following equation.

$Na + Cl_2\rightarrow NaCl$ 

Count the number of atoms on each side of the equation:

TYPE OF ATOM	LEFT HAND SIDE	RIGHT HAND SIDE
$Na$	$1$	$1$
$Cl$	$2$	$1$

The number of $Cl$ atoms is not equal, another $Cl$ is needed on the right hand side. To achieve this add a ' $2$ ' in front of the $NaCl$ :

$Na + Cl_2\rightarrow 2NaCl$

However, if you count the number of atoms again the $Na$ is now unbalanced.

Add a ' $2$ ' in front of the $Na$ reacting material to balance fully:

$2Na + Cl_2\rightarrow 2NaCl$

$\underline{Therefore,\ the\ balanced\ equation\ is\ 2Na + Cl_2\rightarrow 2NaCl}$ .

Ionic equations

An ion is a charged particle. In ionic equations, each substance is represented by their formulae. The total charge is the same on both sides.

procedure

1.	Work out the formulae of the reacting and product materials.
2.	Count the number of atoms on each side and balance the equation as shown in example two.
3.	Once balanced, ensure that the charge is the same on the left hand side to the right.

Example 3

$Na^+ + Cl^-\rightarrow NaCl$

State symbols

State symbols show the physical state of each substance in a reaction. These can be represented to the right of the formulae for a substance in an equation.

state	state symbol
Solid	$(s)$
Liquid	$(l)$
Gas	$(g)$
Aqueous solution	$(aq)$

Example

$sodium(s)+chlorine(g)\rightarrow sodium\,chloride(s)$

$2Na(s) + Cl_2(g) \rightarrow 2NaCl(s)$

Learn with Basics

Length:

Unit 1

An introduction to chemical reactions

Unit 2

Word and symbol equations

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Unit 3