Chemical Reactions and Equations Class 10

Which of the statements about the reaction below are incorrect?
2PbO(s) + C(s) → 2Pb(s) + CO
2
(g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
(i) - (a) and (b)
(ii) - (a) and (c)
(iii) - (a), (b) and (c)
(iv) - all

Fe
2
O
3
+ 2Al → Al
2
O
3
+ 2Fe
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.

What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced

What is a balanced chemical equation? Why should chemical equations be balanced?

Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulfur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Balance the following chemical equations.
(a) HNO
3
+Ca(OH)
2
→ Ca(NO
3
)
2
+ H
2
O

Balance the following chemical equations.
(b) NaOH + H
2
SO
4
→ Na
2
SO
4
+ H
2
O

Balance the following chemical equations.
(c) NaCl + AgNO
3
→ AgCl + NaNO
3

Balance the following chemical equations.
(d) BaCl
2
+ H
2
SO4 → BaSO
4
+ HCl

NCERT Q7
Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
Answer:-
Ca(OH)
2
+ CO
2
→ CaCO
3
+ H
2
O
Name of the element
No. of atoms in reactants
No. of atoms in products
Calcium
1
1
Oxygen
4
4
Hydrogen
2
2
Carbon
1
1
The number of atoms of elements in reactants and products are equal. It does not require any further balancing.
Since all the elements are balanced the final balanced equation is
Ca(OH)
2
+ CO
2
→ CaCO
3
+ H
2
O

NCERT Q7
Write the balanced chemical equations for the following reactions.
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
Answer:-
Zn + AgNO
3
→ Zn(NO
3
)
2
+ Ag
Name of the element
No. of atoms in reactants
No. of atoms in products
Zinc
1
1
Silver
1
1
Nitrogen
1
2
Oxygen
3
6
To balance Nitrogen and Oxygen,
Multiply AgNO
3
by 2
Zn +
2
AgNO
3
→ Zn(NO
3
)
2
+ Ag
Name of the element
No. of atoms in reactants
No. of atoms in products
Zinc
1
1
Silver
2
1
Nitrogen
2
2
Oxygen
6
6
To balance Silver,
Multiply Ag by 2
Zn +
2
AgNO
3
→ Zn(NO
3
)
2
+
2
Ag
Name of the element
No. of atoms in reactants
No. of atoms in products
Zinc
1
1
Silver
2
2
Nitrogen
2
2
Oxygen
6
6
Now, all the elements are balanced and the balanced equation is
Zn +
2
AgNO
3
→ Zn(NO
3
)
2
+
2
Ag

NCERT Q7
Write the balanced chemical equations for the following reactions.
(c) Aluminium + Copper chloride → Aluminium chloride + Copper
Answer:-
(c)
Al + CuCl
2
→ AlCl
3
+ Cu
Name of the element
No. of atoms in reactants
No. of atoms in products
Aluminium
1
1
Copper
1
1
Chlorine
2
3
To balance Chlorine,
Multiply
CuCl
2
by 3 and AlCl
3
by 2
Al +
3
CuCl
2
→
2
AlCl
3
+ Cu
Name of the element
No. of atoms in reactants
No. of atoms in products
Aluminium
1
2
Copper
3
1
Chlorine
6
6
To balance Aluminium,
Multiply
Al by 2
To balance Copper,
Multiply
Cu by 3
2
Al +
3
CuCl
2
→
2
AlCl
3
+
3
Cu
Name of the element
No. of atoms in reactants
No. of atoms in products
Aluminium
2
2
Copper
3
3
Chlorine
6
6
Now, all the elements are balanced and the balanced equation is
2
Al +
3
CuCl
2
→
2
AlCl
3
+
3
Cu

NCERT Q7
Write the balanced chemical equations for the following reactions.
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride
Answer:-
(d) BaCl
2
+ K
2
SO
4
→ BaSO
4
+ KCl
Name of the element
No. of atoms in reactants
No. of atoms in products
Barium
1
1
Chlorine
2
1
Potassium
2
1
Sulphur
1
1
Oxygen
4
4
To balance Chlorine and Potassium,
Multiply KCl by 2
BaCl
2
+ K
2
SO
4
→ BaSO
4
+
2
KCl
Name of the element
No. of atoms in reactants
No. of atoms in products
Barium
1
1
Chlorine
2
2
Potassium
2
2
Sulphur
1
1
Oxygen
4
4
Now, all the elements are balanced and the balanced equation is
BaCl
2
+ K
2
SO
4
→ BaSO
4
+
2
KCl

Write the balanced chemical equation for the following and identify the type of
reaction in each case.
(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) +
Barium bromide(s)
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)

What does one mean by exothermic and endothermic reactions? Give examples.

Why is respiration considered an exothermic reaction? Explain

Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

What is the difference between displacement and double displacement reactions? Write equations for these reactions.

In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

What do you mean by a precipitation reaction? Explain by giving examples.

Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction
Answer:-
Addition of Oxygen
to a Substance is called
Oxidation.
That is,
gain of Oxygen
is called Oxidation.
For example,
2Cu + O
2
→
2CuO
In the above reaction,
Oxygen is being added to Copper, hence it gets oxidised to CuO.
C + O
2
→
CO
2
In the above reaction,
Oxygen is being added to Carbon, hence it gets oxidised to CO
2
.
Removal of Oxygen
from a substance is called
Reduction.
That is,
loss of Oxygen
is called Reduction.
For example,
CuO + H
2
→
Cu + H
2
O
Oxygen is removed from Copper
in the reaction, therefore
reduction
occurs.
Fe
3
O
4
+ 4H
2
→ 3Fe + 4H
2
O
Oxygen is removed from Iron
in the reaction, therefore
reduction
occurs.

A shiny brown coloured element ‘X’ on heating in air becomes black in colour.
Name the element ‘X’ and the black coloured compound formed.

Why do we apply paint on iron articles?

Oil and fat containing food items are flushed with Nitrogen. Why?

Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity

Why should a magnesium ribbon be cleaned before burning in air?

Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride

Write the balanced equation for the following chemical reactions.
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride

Write the balanced equation for the following chemical reactions.
(iii) Sodium + Water → Sodium hydroxide + Hydrogen

Write a balanced chemical equation with state symbols for the
following reactions.
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium Chloride.

Write a balanced chemical equation with state symbols for the
following reactions.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

A solution of a substance ‘X’ is used for white washing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.

Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.

Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Give an example of a double displacement reaction other than the one given in Activity 1.10.

Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(i) 4Na(s) + O
2
(g) → 2Na
2
O(s)
(ii) Cu(s) + H
2
(g) → Cu(s) + H
2
O(l)