PHYSICAL SCIENCE LESSON-2 CHEMICAL EQUATIONS

  PHYSICAL SCIENCE

LESSON-2

CHEMICAL EQUATIONS

Reflections on concepts

Question 1.

What information do you get from a balanced chemical equation?

Answer:

1. A chemical equation gives information about the reactants and products by means of their symbols and formulae.
2. It gives the ratio of molecules of reactants and products.
3. It gives the relative masses of reactants and products.
4. If the masses are expressed in grams, then the equation also gives the molar ratios of reactants and products.
5. We can calculate the volumes of gases liberated at given condition of temperature and pressure using molar mass and molar volume relationship.
6. Using molar mass and Avagadro’s number we can calculate the number of molecules and atoms of different substances.

Question 2.

Why should we balance a chemical equation?

Answer:

Chemical reactions obeys law of conservation of mass. So, the total number of atoms of each element in the reactants must be equal to the total number of atoms of each element in the products. So we should have to balance chemical equation.

Question 3.

Balance the following chemical equations.

(a)  NaOH + H₂SO₄ → Na₂SO₄ + H₂O

Answer:

Step 1: Write unbalanced equation

NaOH + H₂SO₄ → Na₂SO₄ + H₂O

Step 2: Compare number of atoms of each element on both sides. Add the suitable coefficients to balance equation.

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

Step 3 : Make sure the coefficients are reduced to their smallest whole number values.

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

Step 4: Check the answer

(b) KClO₃ → KCl + O₂
Answer:
Step 1: Write unbalanced equation.
KClO₃ → KCl +O₂

Step 2: Add suitable coefficients to balance equation on both sides.
2KClO₃ → 2KCl +3O₂

Step 3: Make sure the coefficients are reduced to their smallest whole number values.
2KClO₃ → 2KCl +3O₂

Step 4: Check the answer.

(c) Hg (NO₃)₂ + Kl → Hg I₂ + KNO₃
Answer:
Step 1: Write unbalanced equation
Hg(NO₃)₂+KI → HgI₂ +KNO₃

Step 2: Add suitable coefficients to balance equation on both sides
Hg(NO₃)₂ +2KI → HgI₂ +2KNO₃

Step 3: Make sure the coefficients are reduced to their smallest whoíe number values.
Hg(NO₃ )₂ +2 Kl → Hg I₂ + 2KNO₃

Step 4: Check the answer

Question 4.
Mention the physical states of the reactants and products of the following chemical reactions and balance the equations.
(a) C₆H₁₂O₆ → C₂H₅OH + CO₂
Answer:
C₆H₁₂O₆(aq) → 2C₂H₅OH(aq)+2CO₂(g)

(b) NH₃ + Cl₂ → N₂ + NH₄Cl^(s)
Answer:
8NH_3(g) +3Cl_2(g) → N_2(g) +6NH₄Cl

(c) Na+H₂O → NaOH+H₂
Answer:
2Na(s)+2H₂O (l) → 2NaOH (aq)+H₂(g)

 

II. Application Of Concepts

Question 1.
Balance the following chemical equations after writing the symbolic representation.
(a) Calcium hydroxide (s) + Nitric acid (aq) → Water(l) + Calcium nitrate(aq)
(b) Magnesium (s) + Iodine(s) → Magnesium Iodide (s)
Answer:
(a) Calcium hydroxide (s) + Nitric acid (aq) → Water(l) + Calcium nitrate(aq)
Answer:
Ca(OH)_2(sol) + 2HNO_3(so1) → 2H₂O_(l) + Ca(NO₃)_2(aq) Double displacement reaction

(b) Magnesium (s) + Iodine(s) → Magnesium Iodide (s)
Answer:
Mg_(s) + I_2(s) → MgI_2(s)
Chemical combination reaction.

Question 2.
Write the following chemical reactions including the physical states of the substances and balance chemical equations
(a)  Sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water.
Answer:
(a) Sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water.
Answer:
NaOH (aq) + HCl (aq) ) → NaCl (aq) +H₂O (l)

(b) Barium chloride reacts with liquid sodium sulphate to leave Barium sulphate as a precipitate and also form liquid sodium chloride.
Answer:
BaCl_2(aq)+ Na₂SO_4(aq) → BaSO₄ ↓ +2 NaCl(aq )

Question 3.
Potassium nitrate and Sodium nitrate reacts separately with copper sulphate solution. Write balanced chemical equations for the above reactions.
Answer:

1. Potassium nitrate reacts with copper sulphate to form potassium sulphate and copper nitrate.
   2KNO₃ + CuSO₄ → K₂SO₄ + Cu(NO₃)₂
   2. Sodium nitrate reacts with copper sulphate to form sodium sulphate and copper nitrate.
   2NaNO₃ + CuSO₄ → Na₂SO₄ + Cu(NO₃)₂

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