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Title: Writing and Balancing chemical equations
Description: The notes are meant to teach students on how to write and balance chemical equations with ease.
Description: The notes are meant to teach students on how to write and balance chemical equations with ease.
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How to Write Chemical Formulae and Balance Chemical Equations
A chemical formula is a concise way of giving information about the atoms that make up a
particular chemical compound
...
The number of atoms (if
greater than one) is shown as a subscript
...
The Law of Conservation of Mass
The mass of a closed system of substances will remain constant, regardless of the processes
acting inside the system
...
For
any chemical process in a closed system, the mass of the reactants must equal the mass of
the products
...
In order to make sure that this is the case, the number of atoms of each element in the
reactants must be equal to the number of atoms of those same elements in the products
...
The substances undergoing reaction are called reactants, and their formulas are placed on the
left side of the
equation
...
The substances generated by the reaction are called products, and their formulas are placed on
the right sight
of the equation
...
Plus signs (+) separate individual reactant and product formulas, and an arrow (⟶) separates
the reactant
and product (left and right) sides of the equation
...
The relative numbers of reactant and product species are represented by coefficients (numbers
placed
immediately to the left of each formula)
...
When balancing a chemical equation, there are a number of steps that need to be followed
...
• STEP 2: Write the equation by putting the reactants on the left of the arrow, and the
products on the right
...
• STEP 4: If the equation is not balanced, change the coefficients of the molecules until the
number of atoms of each element on either side of the equation balance
...
Exercises
Question 1: Balance the following equation:
Mg + HCl → MgCl2 + H2
Answer
Step 1 :
Reactants: Mg = 1 atom; H = 1 atom and Cl = 1 atom
Products: Mg = 1 atom; H = 2 atoms and Cl = 2 atoms
Step 2 : Balance the equation
The equation is not balanced since there are 2 chlorine atoms in the product and only
1 in the reactants
...
The final equation is:
Mg + 2HCl → MgCl2 + H2
Question 2: Balanced the following equation:
Mg + P4 → Mg3P2
Answer
Step 1 Identify the reactants and the products
Reactants: Mg =1
P=4
Products: Mg =3
P=2
The number of Mg and P in the reactants and products is not the same
...
Mg + P4 → 2Mg3P2
Having done that, we need to increase the number of atoms of Mg in the reactants to 6 in order to
balance the equation
...
Question 3: Nitrogen gas reacts with hydrogen gas to form ammonia
...
Answer
Step 1 : Identify the reactants and the products, and write their chemical
Formulae
...
Step 2 : Write the equation so that the reactants are on the left and products
on the right of the arrow
The equation is as follows:
N2 + H2 → NH3
Step 3 : Count the atoms of each element in the reactants and products
Reactants: N = 2; H = 2
Products: N = 1; H = 3
Step 4 : Balance the equation
In order to balance the number of nitrogen atoms, we could rewrite the equation as:
N2 + H2 → 2NH3
Step 5 : Check that the atoms are balanced
In the above equation, the nitrogen atoms now balance, but the hydrogen atoms
don’t (there are 2 hydrogen atoms in the reactants and 6 in the product)
...
The final equation is:
N2 + 3H2 → 2NH3
Now the atoms of both sides of the equations are balanced
...
This is done by
placing the correct label on the right-hand side of the formula
...
(g) for gaseous compounds
2
...
(s) for solid compounds
4
...
A catalyst is a substance that speeds up the
reaction without undergoing any change to itself
...
To show that heat was needed for the reaction, a Greek delta (_) is placed above the arrow in
the same way as the catalyst
...
Calcium nitrate (Ca(NO3)2) is
also produced in the solution
...
Step 2 : Place the reactants on the left of the equation and the products on the right hand side of
the arrow
CaCl2(I) + AgNO3(I) →Ca(NO3)2 (aq) + AgCl(s)
Step 3 : Balance the equation
CaCl2(I) + AgNO3(I) →Ca(NO3)2 (aq) + AgCl(s)
We need to increase the number of atoms of Cl on the right-hand side to be equal to that of the
left-hand side and increase the atoms of nitrate on the left-hand side to be equal to that of the
right-hand side of the equation
...
Write a balanced equation
for this reaction
...
The products are zinc
chloride (ZnCl2) and hydrogen (H2)
...
Zn + HCl → ZnCl2 + H2
Step 3 : Balance the equation
You will notice that the zinc atoms balance but the chlorine and hydrogen atoms
don’t
...
Zn + 2HCl → ZnCl2 + H2
Step 4 : Check that all the atoms balance
When you look at the equation again, you will see that all the atoms are now balanced
...
g
...
(b) Prove that the law of conservation of mass is obeyed during this chemical
reaction
...
P4(s) + 5O2(g) → 2P2O5(s)
Step 3 : Check that the atoms are balanced
The equation is now balanced, as the sum of the atoms of the left-hand side equation is equal to
that of the right-hand of the equation
...
Title: Writing and Balancing chemical equations
Description: The notes are meant to teach students on how to write and balance chemical equations with ease.
Description: The notes are meant to teach students on how to write and balance chemical equations with ease.