Writing a chemical equation
How to write a balanced chemical equation : A Step-by-Step Guide - 10th CBSE- Physical science
Writing a chemical
equation is a crucial aspect regularly featured in the AISSE exam, and it's
imperative for every CBSE 10th-grade student to diligently practice it before
their final examination. To address this need, we've created a blog post
encompassing all significant balanced chemical equations (solved) aligned with
the 10th-grade NCERT curriculum.
Define a chemical equation?
An arrow separates the reactants and products in a chemical equation. Important reaction conditions, such as temperature, pressure, or catalysts, should be indicated on the arrow.
Additionally, the arrowhead points towards the products side, indicating the
direction of the reaction.
To enhance the
informativeness of the chemical equation, the physical states of reactants and
products are specified. The symbol (g) signifies gaseous compounds, (l) denotes
liquid molecules, and (s) represents solid substances.
The energy required to
initiate a chemical reaction is noted on the reactant side, while the energy
released during the chemical transformation is indicated on the product side.
A chemical equation
must adhere to the law of conservation of mass, ensuring balance.
An unbalanced chemical equation is referred to as a skeletal chemical equation, while a chemical equation expressed in words rather than chemical formulas is termed a word equation.
While word equations are the simplest and most convenient method of
representing a chemical change, they tend to be lengthy.
A Step-by-Step guide to balance a chemical equation:
Step 1: Write down the
symbols of elements and the formulas of chemical compounds as presented in the
word equation.
Step 2: Initiate the
balancing process by addressing the compound containing the highest number of
atoms. This may either be a reactant or a product. Within that compound,
identify the element with the highest count of atoms.
Step 3: Similarly,
adjust the count of atoms for all compounds involved to achieve a balanced
chemical equation.
Step 4: Validate the
accuracy of the balanced equation using the trial-and-error method.
Step 5: Conclude by
specifying the physical states of all compounds/elements featured in the given
chemical equation.
For example:
Hydrogen + Chlorine -----------------→ Hydrogen chloride
…………….. [ Word-equation]
H2 + Cl2
---------------→ HCl ……………………… [Skeletal chemical equation]
H2 + Cl2
---------------→ 2HCl ………………………
[Balancing the chemical equation using hit-and-trial method]
H2 (g) + Cl2
(g) ---------------→ 2HCl (g) ……………………… [A balanced chemical
equation]
Important questions and answers on writing a chemical equation:
1. What is a skeletal chemical equation?
Answer:
It is an unbalanced
chemical equation merely presents the word equation using symbols/chemical
formulas of the elements and compounds participating in the chemical
transformation. It does not adhere to the law of conservation of mass.
For instance, in the
formation of magnesium oxide from magnesium and oxygen, upon close observation,
the mass of oxygen on both the reactant and product sides of the chemical
equation remains unbalanced.
Mg + O2
------------→
MgO
Magnesium
oxide
2. What is hit-and-trial method?
Answer:
This approach is
employed to balance skeletal chemical equations in compliance with the law of
conservation of mass.
Through the
hit-and-trial method, we experiment with various combinations of the smallest
whole number coefficients to achieve balance in the chemical equation.
3. What is a balanced chemical equation?
Answer:
It is a method of illustrating the chemical conversion of reactants into products utilizing their chemical formulas.
In the process of balancing a chemical equation, we employ the hit-and-trial method.
A chemical equation must be balanced in accordance
with the law of conservation of mass. Failure to do so means it does not
accurately depict the actual chemical change, which can be verified through
laboratory experiments.
4. What is the law of conservation of mass?
Answer:
As per the law of conservation, mass cannot be created or destroyed during a chemical reaction. Therefore, the total mass of elements in the products must equal the total mass of elements in the reactants.
Put differently, the number of atoms for each element remains constant before and after a chemical reaction.
Writing a chemical
equation in accordance with the law of conservation of mass is termed a
balanced chemical equation. The hit-and-trial method is a well-known approach
used to balance a skeletal chemical equation.
5. Explain the importance of writing the physical states in a chemical equation?
Answer:
When composing a
balanced chemical equation, it is crucial to indicate the physical states of
the compounds/elements participating in the chemical transformation.
This provides insight
into the reaction's nature and the necessary precautions for laboratory
experimentation.
Notations used to
denote the physical states of chemical compounds include: (s) for solids, (l)
for liquids, (g) for gases, and (aq) for aqueous substances, indicating
compounds dissolved in water.
Furthermore, the
balanced chemical equation also indicates the type of energy absorbed or
released during a chemical change.
For instance:
CaO + H2O
---------------→ Ca(OH)2 + heat [ Exothermic reaction]
CaCO3 +
heat energy ---------------→ CaO + CO2 [ Endothermic reaction]
The aforementioned
equation illustrates the release of heat energy during the formation of calcium
hydroxide. Conversely, the decomposition of calcium carbonate involves the
absorption of heat energy.
50 Solved Balanced Chemical Equations: Essential for 10th CBSE AISSE exam
1. Magnesium + Oxygen
-------------→ Magnesium Oxide
Mg + O2
---------→ MgO
Balancing the number
of oxygen atoms on both the sides of the chemical equation, we get;
Mg + O2
---------→ 2MgO
Balancing the number
of magnesium atoms on both the sides of the chemical equation, we get;
2Mg + O2
---------→ 2MgO
Finally, the balanced
chemical equation is;
2Mg + O2
---------→ 2MgO
2. Iron + Water
---------→ Iron (II, III) oxide + Hydrogen
Fe + H2O
----------→ Fe3O4 + H2
Balancing the number
of oxygen atoms on both the sides of the chemical equation, we get;
Fe + 4H2O
----------→ Fe3O4 + H2
Balancing the number
of iron atoms on both the sides of the chemical equation, we get;
3Fe + 4H2O
----------→ Fe3O4 + H2
Balancing the number
of hydrogen atoms on both the sides of the chemical equation, we get;
3Fe + 4H2O
----------→ Fe3O4 + 4H2
Finally, the balanced
chemical equation is;
3Fe + 4H2O
----------→ Fe3O4 + 4H2
3. Zinc + Hydrochloric
acid --------------→ Zinc chloride + Hydrogen
Zn + HCl -------------→
ZnCl2 + H2
Balancing the number
of hydrogen & chlorine atoms on both the sides of the chemical equation, we
get;
Zn + 2HCl
-------------→ ZnCl2 + H2
Finally, the balanced
chemical equation is;
Zn + 2HCl
-------------→ ZnCl2 + H2
4. Hydrogen + Oxygen
--------------→ Water
H2 + O2
-----------→ H2O
Balancing the number
of oxygen atoms on both the sides of the chemical equation, we get;
H2 + O2
-----------→ 2H2O
Balancing the number
of hydrogen atoms on both the sides of the chemical equation, we get;
2H2 + O2
-----------→ 2H2O
The balanced chemical
equation is
2H2 + O2
-----------→ 2H2O
5. Hydrogen + Chlorine
-------------→ Hydrogen chloride
H2 + Cl2
-------------→ HCl
Balancing the number
of hydrogen & chlorine atoms on both the sides of the chemical equation, we
get;
H2 + Cl2
-------------→ 2HCl
The balanced chemical
equation is
H2 + Cl2
-------------→ 2HCl
6. Carbon monoxide +
Hydrogen ---------------→ Methanol
CO + H2
-----------→ CH3OH
CO + 2H2
-----------→ CH3OH
7. Carbon dioxide +
Water -----------→ Glucose + Oxygen + 6 Water
CO2 + H2O -------------→ C6H12O6
+ O2 + 6 H2O
CO2 + 12H2O
-------------→ C6H12O6 + O2 + 6 H2O
6CO2 + 12H2O -------------→ C6H12O6
+ O2 + 6 H2O
6CO2 + 12H2O
-------------→ C6H12O6 + 6O2 + 6 H2O
8. Sodium + Oxygen
----------------→ Sodium Oxide
Na + O2
--------------→ Na2O
Na + O2
--------------→ 2Na2O
4Na + O2
--------------→ 2Na2O
9. Iron + Oxygen
--------------→ Iron (II,III) Oxide
Fe + O2
-------------→ Fe3O4
3Fe + O2
-------------→ Fe3O4
3Fe + 2O2
-------------→ Fe3O4
10. Iron + Oxygen
--------------→ Iron (III) Oxide
Fe + O2
-------------→ Fe2O3
Fe + 3O2
-------------→ Fe2O3
Fe + 3O2
-------------→ 2Fe2O3
4Fe + 3O2
-------------→ 2Fe2O3
11. Aluminium + Oxygen
--------------→ Aluminium Oxide
Al + O2
-------------→ Al2O3
Al + 3O2
-------------→ Al2O3
Al + 3O2
-------------→ 2Al2O3
4Al + 3O2
-------------→ 2Al2O3
12. Silver Chloride
-------------→ Silver + Chlorine
AgCl -------------→ Ag
+ Cl2
2AgCl -------------→
Ag + Cl2
2AgCl -------------→ 2Ag
+ Cl2
13. Silver bromide -------------→
Silver + Bromine
AgBr -------------→ Ag
+ Br2
2AgBr -------------→
Ag + Br2
2AgBr -------------→ 2Ag
+ Br2
14. Sodium
hydroxide + Zinc ----------------→ Sodium zincate + hydrogen
NaOH + Zn
---------------→ Na2ZnO2 + H2
2NaOH + Zn
---------------→ Na2ZnO2 + H2
15. Sodium
carbonate + Hydrochloric acid ---------→ Sodium chloride + water + carbon
dioxide
Na2CO3
+ HCl --------------→ NaCl + H2O + CO2
Na2CO3
+ 2HCl --------------→ NaCl + H2O + CO2
Na2CO3
+ 2HCl --------------→ 2NaCl + H2O + CO2
16. Barium
chloride + Aluminium sulphate ----------→ Barium sulphate + Aluminium chloride
BaCl2
+ Al2(SO4)3 ---------------→ BaSO4
+ AlCl3
BaCl2
+ Al2(SO4)3 ---------------→ 3BaSO4
+ AlCl3
3BaCl2
+ Al2(SO4)3 ---------------→ 3BaSO4
+ AlCl3
3BaCl2
+ Al2(SO4)3 ---------------→ 3BaSO4
+ 2AlCl3
17. Sodium +
water -------------→ Sodium hydroxide + hydrogen
Na + H2O
------------→ NaOH + H2
Na + 2H2O
------------→ NaOH + H2
Na + 2H2O
------------→ 2NaOH + H2
2Na + 2H2O
------------→ 2NaOH + H2
18. Barium
chloride + Sodium sulphate ----------→ Barium sulphate + Sodium chloride
BaCl2
+ Na2SO4 ---------------→ BaSO4 + NaCl
BaCl2
+ Na2SO4 ---------------→ BaSO4 + 2NaCl
19. Sodium
hydroxide + Hydrochloric acid -------------→ Sodium chloride + water
NaOH + HCl
------------→ NaCl + H2O
It is a
balanced chemical equation
20. Methane +
Oxygen ------------→ Carbon dioxide + water
CH4
+ O2 --------------→ CO2 + H2O
CH4
+ O2 --------------→ CO2 + 2H2O
CH4
+ 2O2 --------------→ CO2 + 2H2O
21. Glucose + Oxygen
--------------→ Carbon dioxide + water
C6H12O6
+ O2 ------------→ CO2 + H2O
C6H12O6
+ O2 ------------→ CO2 + 6H2O
C6H12O6
+ O2 ------------→ 6CO2 + 6H2O
C6H12O6
+ 6O2 ------------→ 6CO2 + 6H2O
22. Ferrous sulphate
------------→ Ferric oxide + Sulphur dioxide + Sulphur trioxide
FeSO4
----------------→ Fe2O3 + SO2 + SO3
2FeSO4
----------------→ Fe2O3 + SO2 + SO3
23. Lead nitrate +
Potassium iodide -------------→ Potassium nitrate + Lead iodide
Pb(NO3)2
+ KI ---------------→ KNO3 + PbI2
Pb(NO3)2
+ 2KI ---------------→ KNO3 + PbI2
Pb(NO3)2
+ 2KI ---------------→ 2KNO3 + PbI2
24. Copper + Oxygen
------------→ Cupric oxide
Cu + O2 ---------------→ CuO
Cu + O2 ---------------→ 2CuO
2Cu + O2 ---------------→ 2CuO
25. Carbon + Hydrogen --------------→ Methane
C + H2 --------------→ CH4
C + 2H2 --------------→ CH4
26. Manganese dioxide + Hydrochloric acid ------------------→ Manganese
Chloride + Water + Chlorine
MnO2 + HCl ------------------→ MnCl2 + H2O
+ Cl2
MnO2 + 4HCl ------------------→ MnCl2 + H2O
+ Cl2
MnO2 + 4HCl ------------------→ MnCl2 + 2H2O
+ Cl2
27. Lead nitrate
---------------→ Lead oxide + Nitrogen dioxide + Oxygen
Pb(NO3)2
----------------→ PbO + NO2 + O2
Pb(NO3)2
----------------→ 2PbO + NO2 + O2
2Pb(NO3)2
----------------→ 2PbO + NO2 + O2
2Pb(NO3)2
----------------→ 2PbO + 4NO2 + O2
28. Silver nitrate +
Sodium Chloride ---------------→ Sodium nitrate + Silver Chloride
AgNO3 +
NaCl ---------------→ NaNO3 + AgCl
It is a balanced
chemical equation
29. Lead Oxide + Carbon
-----------------→ Lead + Carbon dioxide
PbO + C
---------------→ Pb + CO2
2PbO + C
---------------→ Pb + CO2
2PbO + C
---------------→ 2Pb + CO2
30. Iron +
Hydrochloric acid -------------------→ Iron (II) Chloride + Hydrogen
Fe + HCl
-------------→ FeCl2 + H2
Fe + 2HCl
-------------→ FeCl2 + H2
31. Ferric oxide +
Aluminium -------------------→ Aluminium oxide + Iron
Fe2O3
+ Al ------------------→ Al2O3 + Fe
Fe2O3
+ Al ------------------→ Al2O3 + 2Fe
Fe2O3
+ 2Al ------------------→ Al2O3 + 2Fe
32. Barium hydroxide +
Ammonium chloride -----------------→ Barium Chloride + Ammonium hydroxide
Ba(OH)2 + NH4Cl
---------------→ BaCl2 + NH4OH
Ba(OH)2 + 2NH4Cl
---------------→ BaCl2 + NH4OH
Ba(OH)2 + 2NH4Cl
---------------→ BaCl2 + 2NH4OH
33. Zinc + Copper
sulphate -------------------→ Zinc sulphate + Copper
Zn + CuSO4
-----------------→ ZnSO4 + Cu
It is a balanced
chemical equation
34. Nitrogen +
Hydrogen -------------→ Ammonia
N2 + H2
-----------------→ NH3
N2 + 3H2
-----------------→ NH3
N2 + 3H2
-----------------→ 2NH3
35. Hydrogen Sulphide
+ Oxygen ------------------→ Water + Sulphur dioxide
H2S + O2
-----------------→ H2O + SO2
H2S + 3O2
-----------------→ H2O + SO2
H2S + 3O2
-----------------→ 2H2O + SO2
2H2S + 3O2
-----------------→ 2H2O + SO2
2H2S + 3O2
-----------------→ 2H2O + 2SO2
36. Potassium + water
------------------→ Potassium hydroxide + hydrogen
K + H2O
----------------→ KOH + H2
K + 2H2O
----------------→ KOH + H2
K + 2H2O
----------------→ 2KOH + H2
2K + 2H2O
----------------→ 2KOH + H2
37. Copper nitrate
-----------------→ Cupric oxide + Nitrogen dioxide + oxygen
Cu(NO3)2
----------------→ CuO + NO2 + O2
Cu(NO3)2
----------------→ 2CuO + NO2 + O2
2Cu(NO3)2
----------------→ 2CuO + NO2 + O2
2Cu(NO3)2
----------------→ 2CuO + 4NO2 + O2
38. Washing soda
---------------→ Sodium carbonate + Water
Na2CO3.10H2O
---------------→ Na2CO3 + H2O
Na2CO3.10H2O
---------------→ Na2CO3 + 10H2O
39. Calcium hydroxide
+ Carbon dioxide ----------------------→ Calcium carbonate + Water
Ca(OH)2 +
CO2 --------------------→ CaCO3 + H2O
It is a balanced
chemical equation
40. Zinc + Silver
nitrate ----------------------→ Zinc nitrate + Silver
Zn + AgNO3
------------------→ Zn(NO3)2 + Ag
Zn + 2AgNO3
------------------→ Zn(NO3)2 + Ag
Zn + 2AgNO3
------------------→ Zn(NO3)2 + 2Ag
41. Aluminium + Copper
(II) Chloride ----------------→ Aluminium Chloride + Copper
Al + CuCl2
-------------------→ AlCl3 + Cu
Al + 3CuCl2
-------------------→ AlCl3 + Cu
Al + 3CuCl2
-------------------→ 2AlCl3 + Cu
2Al + 3CuCl2
-------------------→ 2AlCl3 + Cu
2Al + 3CuCl2
-------------------→ 2AlCl3 + 3Cu
42. Barium chloride + Potassium
sulphate ----------→ Barium sulphate + Potassium chloride
BaCl2
+ K2SO4 ---------------→ BaSO4 + KCl
BaCl2
+ K2SO4 ---------------→ BaSO4 + 2KCl
43. Sodium bicarbonate
+ Hydrochloric acid -----------------→ Sodium Chloride + Water + Carbon dioxide
NaHCO3 +
HCl ----------------→ NaCl + H2O + CO2
It is a balanced
chemical equation
44. Nitric acid + Calcium
hydroxide ------------------→ Calcium nitrate + Water
HNO3 +
Ca(OH)2 -------------------→ Ca(NO3)2 + H2O
2HNO3 +
Ca(OH)2 -------------------→ Ca(NO3)2 + H2O
2HNO3 +
Ca(OH)2 -------------------→ Ca(NO3)2 + 2H2O
45. Sodium hydroxide +
Sulphuric acid -------------------→ Sodium sulphate + Water
NaOH + H2SO4
----------------→ Na2SO4 + H2O
2NaOH + H2SO4
----------------→ Na2SO4 + H2O
2NaOH + H2SO4
----------------→ Na2SO4 + 2H2O
46. Sodium chloride +
Silver nitrate ----------------→ Sodium nitrate + Silver Chloride
NaCl + AgNO3
--------------→ NaNO3 + AgCl
It is a balanced
chemical equation
47. Barium Chloride +
Sulphuric acid ----------------→ Barium sulphate + Hydrochloric acid
BaCl2 + H2SO4
------------------→ BaSO4 + HCl
BaCl2 + H2SO4
------------------→ BaSO4 + 2HCl
48. Calcium hydroxide
+ Hydrochloric acid ---------------→ Calcium chloride + Water
Ca(OH)2 +
HCl -------------→ CaCl2 + H2O
Ca(OH)2 + 2HCl
-------------→ CaCl2 + H2O
Ca(OH)2 + 2HCl
-------------→ CaCl2 + 2H2O
49. Sodium carbonate +
Hydrochloric acid -------------→ Sodium chloride + water + carbon dioxide
Na2CO3
+ HCl ------------→ NaCl + H2O + CO2
Na2CO3
+ HCl ------------→ 2NaCl + H2O + CO2
Na2CO3
+ 2HCl ------------→ 2NaCl + H2O + CO2
50. Potassium bromide
+ Barium iodide ---------------→ Potassium iodide + Barium bromide
KBr + BaI2
----------------→ KI + BaBr2
KBr + BaI2
----------------→ 2KI + BaBr2
2KBr + BaI2
----------------→ 2KI + BaBr2