Category: Questions

Answer:

A reaction in which an insoluble solid (called precipitate) is formed is called a precipitation reaction.

Example 1:

CaCl2 (aq) + Na2CO3 (aq) → CaCO3 (s) + 2 NaCl (aq)

In this reaction, calcium carbonate (CaCO₃) is obtained as a precipitate. Hence, it is a precipitation reaction.

Example 2:

BaCl2 (aq) + Na2SO4 (aq) → BaSO4 (s) + 2 NaCl (aq)

In this reaction, barium sulphate (BaSO₄) is obtained as a precipitate.

Answer:

In the refining of silver, copper metal displaces silver from its solution of silver nitrate. This is a typical displacement reaction, where a more reactive metal (copper) replaces a less reactive metal (silver) from its compound.

Cu (copper) + 2 AgNO3 (silver nitrate) → Cu(NO3)2 (copper nitrate) + 2 Ag (silver)

Substances Involved:

• Copper (Cu)
• Silver nitrate (AgNO₃)
• Copper nitrate (Cu(NO₃)₂)
• Silver (Ag)

Answer:

Displacement Reaction:
In a displacement reaction, a more reactive element replaces a less reactive element from a compound. Here, element A is more reactive than element B.

Zn (zinc) + CuSO4 (copper sulfate) → ZnSO4 (zinc sulfate) + Cu (copper)

Substances Involved:

• Zinc (Zn)
• Copper sulfate (CuSO₄)
• Zinc sulfate (ZnSO₄)
• Copper (Cu)

Double Displacement Reaction:
In a double displacement reaction, two atoms or a group of atoms switch places to form new compounds.

NaCl (sodium chloride) + AgNO3 (silver nitrate) → NaNO3 (sodium nitrate) + AgCl (silver chloride)

Substances Involved:

• Sodium chloride (NaCl)
• Silver nitrate (AgNO₃)
• Sodium nitrate (NaNO₃)
• Silver chloride (AgCl)

Answer:

(a) Thermal Decomposition:
When heat is used to decompose a substance.

CaCO3 (calcium carbonate) → CaO (calcium oxide) + CO2 (carbon dioxide)

Substances Involved:

• Calcium carbonate (CaCO₃)
• Calcium oxide (CaO)
• Carbon dioxide (CO₂)

(b) Decomposition by Light:
When light is used to decompose a substance.

2 AgCl (silver chloride) → 2 Ag (silver) + Cl2 (chlorine)

Substances Involved:

• Silver chloride (AgCl)
• Silver (Ag)
• Chlorine (Cl₂)

(c) Decomposition by Electricity:
When electricity is used to decompose a substance.

2 H2O (water) → 2 H2 (hydrogen) + O2 (oxygen)

Substances Involved:

• Water (H₂O)
• Hydrogen (H₂)
• Oxygen (O₂)

Answer:

Decomposition reactions are those in which a compound breaks down to form two or more substances. These reactions require a source of energy to proceed. Thus, they are the exact opposite of combination reactions in which two or more substances combine to give a new substance with the release of energy.

Decomposition Reaction:

CaCO3 (calcium carbonate) → CaO (calcium oxide) + CO2 (carbon dioxide)

Substances Involved:

• Calcium carbonate (CaCO₃)
• Calcium oxide (CaO)
• Carbon dioxide (CO₂)

Combination Reaction:

2 H2 (hydrogen) + O2 (oxygen) → 2 H2O (water)

Substances Involved:

• Hydrogen (H₂)
• Oxygen (O₂)
• Water (H₂O)

Answer:

Energy is required to support life. The energy in our body is obtained from the food we eat. During digestion, large molecules of food are broken down into simpler substances such as glucose. Glucose then combines with oxygen in the cells and provides energy. The special name for this combustion reaction is respiration. Since energy is released during the whole process, it is considered an exothermic process.

Chemical Equation for Respiration:

C6H12O6 (glucose) + 6 O2 (oxygen) → 6 CO2 (carbon dioxide) + 6 H2O (water) + Energy

Substances Involved:

• Glucose (C₆H₁₂O₆)
• Oxygen (O₂)
• Carbon dioxide (CO₂)
• Water (H₂O)

Answer:

Exothermic Reactions:

Exothermic reactions are chemical reactions that release energy in the form of heat, light, or sound. In these reactions, the energy of the products is lower than the energy of the reactants, leading to the release of energy.

Example: A mixture of sodium (Na) and chlorine (Cl₂) reacts to form table salt (NaCl). This is a combination reaction that releases energy in the form of heat and light.

2 Na (solid) + Cl2 (gas) → NaCl (solid)

Substances Involved:

• Sodium (Na) – Solid
• Chlorine (Cl₂) – Gas
• Sodium chloride (NaCl) – Solid

Endothermic Reactions:

Endothermic reactions are chemical reactions that absorb energy or require energy in order to proceed. In these reactions, the energy of the products is higher than the energy of the reactants, leading to the absorption of energy.

Example: Photosynthesis is an example of an endothermic reaction. In this process, plants use the energy from sunlight to convert carbon dioxide (CO₂) and water (H₂O) into glucose (C₆H₁₂O₆).

6 CO2 (gas) + 6 H2O (liquid) → C6H12O6 (aqueous) + 6 O2 (gas)

Substances Involved:

• Carbon dioxide (CO₂) – Gas
• Water (H₂O) – Liquid
• Glucose (C₆H₁₂O₆) – Aqueous
• Oxygen (O₂) – Gas

Catalyst: Sunlight (provides energy for the reaction)

Balanced Equations and Reaction Types:

1. (a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)

   2 KBr (aq) + BaI₂ (aq) → 2 KI (aq) + BaBr₂ (s)

   Type of Reaction: Double displacement (precipitation) reaction.
2. (b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)

   ZnCO₃ (s) → ZnO (s) + CO₂ (g)

   Type of Reaction: Decomposition reaction.
3. (c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)

   H₂ (g) + Cl₂ (g) → 2 HCl (g)

   Type of Reaction: Combination (synthesis) reaction.
4. (d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)

   Mg (s) + 2 HCl (aq) → MgCl₂ (aq) + H₂ (g)

   Type of Reaction: Single displacement (redox) reaction.

Balanced Equations:

1. (a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water

   Ca(OH)₂ (aq) + CO₂ (g) → CaCO₃ (s) + H₂O (l)

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

   Zn (s) + 2 AgNO₃ (aq) → Zn(NO₃)₂ (aq) + 2 Ag (s)

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

   2 Al (s) + 3 CuCl₂ (aq) → 2 AlCl₃ (aq) + 3 Cu (s)

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

   BaCl₂ (aq) + K₂SO₄ (aq) → BaSO₄ (s) + 2 KCl (aq)

Balanced Equations:

1. (a) HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O

   2 HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2 H₂O

2. (b) NaOH + H₂SO₄ → Na₂SO₄ + H₂O

   2 NaOH + H₂SO₄ → Na₂SO₄ + 2 H₂O

3. (c) NaCl + AgNO₃ → AgCl + NaNO₃

   NaCl + AgNO₃ → AgCl + NaNO₃

4. (d) BaCl₂ + H₂SO₄ → BaSO₄ + HCl

   BaCl₂ + H₂SO₄ → BaSO₄ + 2 HCl