Answer the following questions : a) What are the raw materials for the production of paper ? [2] b) Draw the flowsheet diagram for the manufacture of Portland cement. [3] c) Nuclear fusion reaction…

a) Raw materials for the production of paper

The production of paper primarily relies on the following raw materials:

• Cellulose: The main raw material, obtained from wood pulp (softwoods like pine and spruce or hardwoods like eucalyptus), agricultural residues (e.g., straw, bagasse), or recycled paper. Cellulose fibers provide the structural framework of paper.
• Water: Used as a medium for processing pulp and as a solvent for chemicals.
• Chemicals:
  • Sodium hydroxide (NaOH) and sodium sulphite (Na₂SO₃): Used in the Kraft process to break down lignin and extract cellulose from wood.
  • Calcium carbonate (CaCO₃) and clay (kaolin): Added as fillers to improve opacity, smoothness, and printability.
  • Rosin and alum (aluminium sulphate, Al₂(SO₄)₃): Used as sizing agents to control ink absorption and improve water resistance.
  • Bleaching agents: Such as chlorine dioxide (ClO₂) or hydrogen peroxide (H₂O₂) to whiten the pulp.
• Energy: Steam and electricity for mechanical processing (e.g., grinding, refining, and drying).
• Recycled paper: Used in the production of recycled paper, which is processed to remove contaminants and separate fibers.

H₂O₂ (Bleaching Agent)H₂O₂ (Bleaching Agent)

---

b) Flowsheet diagram for the manufacture of Portland cement

Explanation of the process:

1. Raw Materials: Limestone (CaCO₃) and clay (SiO₂, Al₂O₃, Fe₂O₃) are crushed and mixed in the ratio of 3:1 or 4:1. Gypsum (CaSO₄·2H₂O) is added later.
2. Crushing & Grinding: The raw materials are ground into a fine powder.
3. Mixing: The powder is mixed uniformly.
4. Heating in Rotary Kiln: The mixture is heated to 1450°C, forming clinker nodules containing:
   • Tricalcium silicate (3CaO·SiO₂ or C₃S)
   • Dicalcium silicate (2CaO·SiO₂ or C₂S)
   • Tricalcium aluminate (3CaO·Al₂O₃ or C₃A)
   • Tetracalcium aluminoferrite (4CaO·Al₂O₃·Fe₂O₃ or C₄AF)
5. Gypsum Addition: Gypsum is added to control the setting time of cement.
6. Final Grinding: The clinker is ground into a fine powder to produce Portland cement.

---

c) Why is a nuclear fusion reaction also called a thermonuclear reaction?

A nuclear fusion reaction is called a thermonuclear reaction because it requires extremely high temperatures (typically millions of degrees Kelvin) to overcome the Coulomb repulsion between positively charged nuclei. The term "thermo" refers to the heat energy required to initiate and sustain the reaction.

Key reasons:

• High Activation Energy: Fusion reactions (e.g., ${}_{}^{}{}_1^2\mathrm{H}+{}_{}^{}{}_1^3\mathrm{H}\to {}_{}^{}{}_2^4\mathrm{He}+{}_{}^{}{}_0^1\mathrm{n}+17.6\mathrm{MeV}$) involve combining light nuclei (e.g., hydrogen isotopes) into heavier nuclei, releasing vast energy. However, the nuclei must collide with sufficient kinetic energy to overcome electrostatic repulsion.
• Plasma State: At such high temperatures, matter exists as a plasma (ionized gas), where electrons are stripped from atoms, allowing nuclei to fuse.
• Natural Occurrence: In stars (e.g., the Sun), fusion occurs naturally due to gravitational compression generating temperatures of 15–20 million K in the core.
• Artificial Initiation: In artificial settings (e.g., hydrogen bombs or fusion reactors), external heat (e.g., from fission or lasers) is used to achieve the required conditions.

Thus, the term "thermonuclear" emphasizes the thermal energy dependency of fusion reactions.

---

d) Formation of addition and condensation polymers

Addition Polymers

• Formation: Formed by the addition reaction of unsaturated monomers (containing double or triple bonds, e.g., alkenes) without the loss of any small molecules.
• Mechanism: The double bonds in monomers (e.g., ethene) break, and the monomers link together to form long chains.
• Example:
  • Polyethene (from ethene): $$n\mathrm{CH}{}_2=\mathrm{CH}{}_2\to [-\mathrm{CH}{}_2-\mathrm{CH}{}_2{}^{-}]\mathrm{n}$$
  • Polystyrene (from styrene): $$n\mathrm{CH}{}_2=\mathrm{CH}(\mathrm{Ph})\to [-\mathrm{CH}{}_2-\mathrm{CH}(\mathrm{Ph}){}^{-}]\mathrm{n}$$

styrenestyreneInitiator (e.g., benzoyl peroxide)[-CH₂-CH(Ph)-]n

Condensation Polymers

• Formation: Formed by the condensation reaction between monomers, where small molecules (e.g., water, methanol, HCl) are eliminated as byproducts.
• Mechanism: Typically involves step-growth polymerization, where functional groups (e.g., –OH, –COOH, –NH₂) react to form bonds (e.g., ester or amide linkages) and release a molecule.
• Example:
  • Nylon-6,6 (from hexamethylenediamine and adipic acid): $$n\mathrm{HOOC}-(\mathrm{CH}{}_2){}_4-\mathrm{COOH}+n\mathrm{H}{}_2\mathrm{N}-(\mathrm{CH}{}_2){}_6-\mathrm{NH}{}_2\to [-\mathrm{OC}-(\mathrm{CH}{}_2){}_4-\mathrm{CO}-\mathrm{NH}-(\mathrm{CH}{}_2){}_6-\mathrm{NH}{}^{-}]\mathrm{n}+2n\mathrm{H}{}_2\mathrm{O}$$
  • Terylene (PET) (from ethylene glycol and terephthalic acid): $$n\mathrm{HO}-(\mathrm{CH}{}_2){}_2-\mathrm{OH}+n\mathrm{HOOC}-\mathrm{C}{}_6\mathrm{H}{}_4-\mathrm{COOH}\to [-\mathrm{O}-(\mathrm{CH}{}_2){}_2-\mathrm{O}-\mathrm{CO}-\mathrm{C}{}_6\mathrm{H}{}_4-\mathrm{CO}{}^{-}]\mathrm{n}+2n\mathrm{H}{}_2\mathrm{O}$$

Comparison Table: