Unit Overview

Nitrogen and sulfur

CIE A-Level Chemistry· 5 min read 📊 n/a

1. Unit at a Glance

Nitrogen (group 15) and sulfur (group 16) are non-metals with outsized importance for global food production, manufacturing, and climate. The unit splits logically into two core sub-topics covering each element and its derivatives, connecting atomic structure, bonding, reactivity and real-world impact.

You will first investigate nitrogen's strong triple bond and resulting inertness, before moving to key industrial processes like Haber ammonia production, and the role of nitrogen oxides in atmospheric pollution. Next, you will explore sulfur chemistry, including the Contact process for sulfuric acid and the link between sulfur emissions and acid rain.

This unit contains two core sub-topics, to be completed in order:

Nitrogen and its compounds

Covers nitrogen gas, ammonia, the Haber process, ammonium salts, nitrates, and nitrogen oxides.

★★⏱ 15 min

Sulfur and its compounds

Explores sulfur allotropes, sulfur dioxide, sulfuric acid, the Contact process, and sulfur's environmental impacts.

★★⏱ 12 min

2. Common Pitfalls

Wrong move:

Confusing the catalyst for the Haber process and the Contact process

Why:

Both are key industrial reversible reactions that appear regularly in exam questions

Correct move:

Haber uses an iron catalyst; Contact uses a vanadium(V) oxide ( $V_{2} O_{5}$ ) catalyst

Wrong move:

Forgetting why nitrogen gas is relatively unreactive

Why:

Exam questions frequently ask to explain nitrogen's inertness

Correct move:

Always link nitrogen's lack of reactivity to the very high bond enthalpy of the N≡N triple bond

3. Quick Reference Cheatsheet

Concept	Key Fact / Equation
N≡N bond enthalpy	+945 kJ mol⁻¹ (very strong)
Haber process equilibrium	$N_{2} (g) + 3 H_{2} (g) ⇌ 2 N H_{3} (g)$
Haber process conditions	450°C, 200 atm, Fe catalyst
Contact process equilibrium	$2 S O_{2} (g) + O_{2} (g) ⇌ 2 S O_{3} (g)$
Contact process conditions	450°C, 1-2 atm, $V_{2} O_{5}$ catalyst
Acid rain formation from $S O_{2}$	$S O_{2} (g) + H_{2} O (l) \to H_{2} S O_{3} (a q)$
Concentrated $H_{2} S O_{4}$ as oxidizing agent	Reacts with metals to produce $S O_{2}$

What's Next

Start this unit by working through the first sub-topic on nitrogen and its compounds, which builds the foundation for understanding the reactive compounds of this key element. After completing both sub-topics in this unit, you can move on to the next topic in the CIE A-Level 9701 syllabus.