Chemical Reactions and Equations Question Answers part 2

Q.1. Which of the statements about the reaction below are incorrect?
2Pb0 (s) + C (s) → 2Pb (s) + CO₂(g)
(a) Lead is getting reduced
(b) Carbon dioxide is getting oxidised
(c) Carbon is getting oxidised
(d) Lead oxide is getting reduced

A. (a) and (b)
B. (a) and (c)
C. (a), (b) and (c)
D. all

Answer :
A


Loss of Oxygen is by an element is known Reduction whereas gain of Oxygen by an element is known as Oxidation 
During this reaction, Lead Oxide(PbO) is getting reduced as it is losing oxygen whereas Carbon(C) is getting oxidised as it is gaining oxygen to form carbon dioxide.

Q.2.Fe₂0₃ + 2Al → Al₂0₃ + 2Fe
The above reaction is an example of a:

A. combination reaction
B. double displacement reaction
C. decomposition reaction
D. displacement reaction

Answer :
D

When an element displaces another element from its compound, a displacement reaction occurs.
In this reaction, aluminium displaces the iron from its compound. Thus, this is an example of displacement reaction.

Q.3. What happens when dilute hydrochloric acid is added to iron filings? 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

Answer :
A

When dilute hydrochloric acid is added to iron fillings, hydrogen gas and iron chloride are produced.


Q.4. What is a balanced chemical equation? Why should chemical equations be balanced?

Answer :
A chemical reaction which have an equal number of atoms of different elements in the reactants and product sides is called a balanced chemical equation. For example;

In the above reaction; zinc reacts with sulphuric acid to form zinc sulphate and hydrogen. Let us examine the number of atoms of different elements on both sides of the arrow.

As the number of atoms of each element is the same on both sides of the arrow, hence, it is a balanced chemical equation.
The chemical equations are balanced to satisfy the law of conservation of mass which says that 'matter (or atoms) can neither be created nor destroyed in a chemical reaction'. So, the total mass of the elements present in the products of a chemical reaction should be equal to the total mass of the elements present in the reactants. In other words, the number of atoms of each element remains the same, before and after a chemical reaction.


Q.5. 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 sulphur dioxide.

(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride solution and a precipitate of barium sulphate.

(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen

Answer :
(a) H₂ (g) + N₂ (g) → NH₃ (g)
Step 1 - To balance chemical equations, first list the number of atoms of different type that are present in the chemical equation on both sides –

Elements	No of Atoms in LHS	No of Atoms in RHS
H	2	3
N	2	1

 
Step 2 - To start balancing, we take any one compound. We will take H₂ on the reactant side in consideration. Let’s start with that. 

Atoms of H2	In Reactant	In Product
Initial	2	3
Balanced	2x3=6	3x2

Hence the Balanced Chemical Equation is 3H₂+ N_2→ 2NH₃
The following questions are solved similarly
(b) 2H₂S (g) + 3O₂ (g) → 2H₂O (l) + 2SO₂ (g)
(c) 3BaCl₂ (aq) + Al₂(SO₄)₃ (aq) → 2AlCl₃ (aq) + 3BaSO₄ (s)
(d) 2K (s) + 2H₂O (l) → 2KOH (aq) + H₂ (g)


Q.6. Balance the following chemical equations:
(a) HNO₃ + Ca(OH)₂→ Ca(NO₃)₂ + H₂O
(b) NaOH + H₂SO₄→ Na₂SO₄ + H₂O
(c) NaCl + AgNO₃→ AgCl + NaNO₃
(d) BaCl₂ + H₂SO₄→ BaSO₄ + 2HCL

Answer :
(a) Step 1 - To balance chemical equations, first list the number of atoms of different type that are present in the chemical equation on both sides -
HNO₃ + Ca(OH)₂→ Ca(NO₃)₂ + H₂O

Element	No. of atoms in LHS	No. of atoms in RHS
N	1	2
Ca	1	1
H	1+2=3	2
O	3+2=5	6+1=7

Step 2 - To start balancing, we find the compound that has the highest number of atoms. We can see that Ca(NO₃)₂ on the product side has the highest number of atoms. In this compound Oxygen has the highest number of atoms. Lets start with that. 

Atoms of O	In Reactant	In Product
Initial	3 + 2=5	6 + 1=7
Balanced	2x3 + 2=8	6 + 2x1=8

This makes the partially balanced equation -
2HNO₃ + Ca(OH)₂→ Ca(NO₃)₂ + 2H₂O
Step 3 - Now checking for all other elements we note that the number of atoms on both side are same. We can say that the equation is balanced. 
(b)NaOH + H₂SO₄→ Na₂SO₄ + H₂O
Step 1 - To balance chemical equations, first list the number of atoms of different type that are present in the chemical equation on both sides –
NaOH + H₂SO₄→ Na₂SO₄ + H₂O

Elements	No of Atoms in LHS	No of Atoms in RHS
Na	1	2
O	1+4=5	5
S	1	1
H	3	2

Step 2 - To start balancing, we take any one compound. We will take NaOH on the reactant side in consideration. Let’s start with that. 

Atoms of Na	In Reactant	In Product
Initial	1	2
Balanced	1x2=2	2

 This makes the partially Balanced Equation as:-
2NaOH + H₂SO₄-> Na₂SO₄ + 2H₂O
Step 3 - Now checking for all other elements we note that the numbers of atoms on both sides are same. We can say that the equation is balanced. 
(c) NaCl + AgNO₃→ AgCl + NaNO₃
Step 1 - To balance chemical equations, first list the number of atoms of different type that are present in the chemical equation on both sides –
NaCl + AgNO₃→ AgCl + NaNO₃

Elements	No of Atoms in LHS	No of Atoms in RHS
Na	1	1
Cl	1	1
Ag	1	1
N	1	1
O	3	3

_{We can see that the Number of Atoms in LHS and RHS are equal, Hence the equation is balanced}
(d) BaCl₂ + H₂SO₄→ BaSO₄ + 2HCL
Step 1 - To balance chemical equations, first list the number of atoms of different type that are present in the chemical equation on both sides –
BaCl₂ + H₂SO₄→ BaSO₄ + 2HCL

Elements	No of Atoms in LHS	No of Atoms in RHS
Ba	1	1
Cl	2	2
H	2	2
S	1	1
0	4	4

 _{We can see that the Number of Atoms in LHS and RHS are equal, Hence the equation is balanced}.


Q.7. Write the balanced chemical equations for the following reactions:
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water

(b) Zinc + Silver nitrate → Zinc nitrate + Silver

(c) Aluminium + Copper chloride → Aluminium chloride + Copper

(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

Answer :
(a) Ca(OH)₂ + Co₂→ CaC0₃ + H₂0
(b) Zn + 2AgNO₃→ Zn(NO₃)₂ + 2Ag
(c) 2Al + 3CuCl₂→ 2AlCl₃ + 3Cu
(d) BaCl₂ + K₂SO₄→ BaSO₄ + 2KCl


Q.8. 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 + Hydrochloric →Magnesium chloride (aq) + Hydrogen (g)

Answer :
(a) Double displacement reaction (also known as precipitation reaction):-
2KBr (aq) + BaI₂ (aq) → 2KI(q) + BaBr₂ (s)
(b) Decomposition reaction:
ZnC0₃ (s) → ZnO (s) + C0₂ (g)

(c) Combination reaction:
H₂ (g) + Cl₂ (g) → 2HCl (g)

(d) Displacement reaction:
Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)