Key Formulae from p-Block Chemistry

1. Stoichiometry and Chemical Reactions

• Molecular Nitrogen (N₂) Production:
• • Laboratory Preparation: ${\text{NH}}_4\text{Cl}+{\text{NaNO}}_2\to {\text{N}}_2+2{\text{H}}_2\text{O}+\text{NaCl}$
  • Explanation: This reaction is used in laboratory settings to produce nitrogen gas. Ammonium chloride reacts with sodium nitrite to produce nitrogen gas along with water and sodium chloride.
• Phosphorus Pentachloride Decomposition:
• • Thermal Decomposition: ${\text{PCl}}_5\to {\text{PCl}}_3+{\text{Cl}}_2$
  • Explanation: When heated, phosphorus pentachloride decomposes into phosphorus trichloride and chlorine gas.

2. Thermodynamics

• Enthalpy of Formation of Ammonia:
• • Haber Process: ${\text{N}}_2(g)+3{\text{H}}_2(g)\rightleftharpoons 2{\text{NH}}_3(g);\Delta H=-46.1,\text{kJ/mol}$
  • Explanation: The formation of ammonia from nitrogen and hydrogen gases is an exothermic reaction, which releases 46.1 kJ/mol of energy.
• Bond Dissociation Enthalpy:
• • For Nitrogen: ${\text{N}}_2(g)\to 2\text{N}(g);\Delta H=941.4,\text{kJ/mol}$
  • Explanation: The dissociation of a nitrogen molecule into two nitrogen atoms requires a high amount of energy due to the triple bond in N₂.

3. Chemical Bonding and Structure

• Electronic Configuration of p-block elements:
• • General Configuration: ${\text{ns}}^2{\text{np}}^{1-6}$
  • Explanation: The general electronic configuration for p-block elements ranges from ns²np¹ to ns²np⁶, depending on their position in the periodic table.
• Oxidation States:
• • Oxidation States in Group 15 Elements: $\text{-3, +3, +5}$
  • Explanation: The common oxidation states for elements in Group 15, with stability varying down the group due to the inert pair effect.

4. Example Applications

• Calculation of Theoretical Yield:
  Solution:
• • For the reaction: ${\text{NH}}_4\text{Cl}+{\text{NaNO}}_2\to {\text{N}}_2+2{\text{H}}_2\text{O}+\text{NaCl}$
  • Example: Calculate the amount of nitrogen gas produced if 10 g of ammonium chloride reacts with excess sodium nitrite.
• • Molar mass of $N{H}_{4}Cl=53.5$ g/mol
  • Moles of $N{H}_{4}Cl=10g/53.5g/mol=0.187mol$
  • From the balanced equation, 1 mole of $N{H}_{4}Cl$ produces 1 mole of $N_2$.
  • Therefore, 0.187 mol of $N{H}_{4}Cl$ will produce 0.187 mol of $N_2$ gas.
  • Molar mass of $N_2$ = 28 g/mol
  • Mass of $N_2=0.187mol\times 28g/mol=5.236g$

5. Common Mistakes

• Incorrect Stoichiometric Calculations:
• • Common Error: Failing to balance chemical equations before performing stoichiometric calculations.
  • Strategy to Avoid: Always ensure the chemical equation is balanced before calculating reactant or product quantities.
• Misinterpretation of Oxidation States:
• • Common Error: Confusing the oxidation states of elements in compounds, particularly in redox reactions.
  • Strategy to Avoid: Practice determining oxidation states using rules consistently and understand periodic trends.