Chemistry · Class 11 · Hydrogen · Term 3

Properties and Uses of Dihydrogen

Investigate the physical and chemical properties of dihydrogen, including its reactions with non-metals, metals, and organic compounds, and explore its major industrial uses.

TL;DR:Let's investigate dihydrogen, a simple molecule with a huge impact, from creating fertilisers that feed our nation to powering the rockets that explore space.

• CBSE Learning Outcomes
• NCERT Class 11 Chemistry: Unit 9 - Hydrogen

About This Topic

This topic, 'Properties and Uses of Dihydrogen', is a fundamental component of the 'Hydrogen' chapter in the Class 11 chemistry curriculum, as prescribed by NCERT and followed by CBSE and other state boards. It builds upon students' prior knowledge of chemical bonding and redox reactions. The focus is on dihydrogen's unique dual nature: its ability to act as a potent reducing agent in most reactions, yet also behave as an oxidising agent when reacting with highly electropositive metals to form hydrides. This duality is central to understanding its unique, and often debated, position in the periodic table.

For the Indian context, the industrial applications are particularly significant. A deep dive into the Haber process for ammonia synthesis is crucial, as it directly links chemistry to the nation's agricultural sector through the production of fertilisers. Similarly, the hydrogenation of vegetable oils to produce vanaspati ghee is a relatable, everyday example of industrial organic chemistry. The topic also serves as a gateway to discussing future energy solutions, like hydrogen fuel cells, which is a growing area of interest and research in India, aligning with national goals for sustainable development and cleaner energy.

Key Questions

1. Explain why dihydrogen acts as a good reducing agent.
2. Analyse the reaction of dihydrogen with nitrogen in the Haber process for ammonia synthesis.
3. Identify three major industrial applications of dihydrogen and explain their chemical basis.

Learning Objectives

• Describe the physical and chemical properties of dihydrogen with appropriate examples.
• Explain the role of dihydrogen as a reducing agent in both inorganic and organic reactions.
• Write balanced chemical equations for the reactions of dihydrogen with metals, non-metals, and organic compounds.
• Analyse the industrial significance of the Haber process for ammonia synthesis and the hydrogenation of oils.
• Justify the unique position of hydrogen in the periodic table by comparing its properties with those of alkali metals and halogens.

Key Vocabulary

Dihydrogen	The diatomic molecule, H₂, which is the most common form of the element hydrogen.
Hydride	A compound of hydrogen with another, more electropositive element. For example, sodium hydride (NaH).
Hydrogenation	A chemical reaction that adds hydrogen across double or triple bonds, typically in organic molecules, often using a catalyst.
Haber Process	The industrial process used to manufacture ammonia from dihydrogen and dinitrogen gases at high pressure and temperature with a catalyst.
Reducing Agent	A substance that donates electrons in a redox reaction, causing another substance to be reduced.

Watch Out for These Misconceptions

Common Misconception

Hydrogen is an alkali metal because it is in Group 1.

What to Teach Instead

While hydrogen is placed in Group 1 due to its 1s¹ electron configuration, it is a non-metal. It resembles alkali metals by forming a H⁺ ion, but it also resembles halogens (Group 17) by forming a hydride ion (H⁻), justifying its unique position.

Common Misconception

Hydrogen fuel is perfectly 'clean' and has no environmental impact.

What to Teach Instead

While burning dihydrogen produces only water, most of the world's hydrogen is currently produced from natural gas (steam reforming), which releases carbon dioxide. Truly 'green' hydrogen must be produced using renewable energy for electrolysis, which is currently expensive and less common.

Common Misconception

Dihydrogen is a weak reactant because the H-H bond is strong.

What to Teach Instead

The H-H bond does have a very high bond enthalpy, which makes dihydrogen relatively inert at room temperature. However, at high temperatures or with a catalyst, it becomes highly reactive and participates in a vast number of important chemical reactions.

Active Learning Ideas

Concept Mapping

Modelling the Haber Process

Students use different coloured clay balls and toothpicks to represent nitrogen and hydrogen atoms and their bonds. They physically break the strong N≡N triple bond and H-H single bonds and then form new N-H bonds to create ammonia molecules, helping them visualise the stoichiometry and energy changes involved.

20 min·Small Groups

Jigsaw

Hydrogenation Jigsaw

Divide students into 'expert' groups, each focusing on one major use of dihydrogen (e.g., ammonia synthesis, hydrogenation of oils, methanol production, metallurgy). They then regroup into 'jigsaw' groups with one expert from each area to teach their peers, ensuring comprehensive learning.

30 min·Small Groups

Concept Mapping

Predict the Product Worksheet

Students are given a worksheet with various reactants (e.g., Cl₂, Na, CuO, C₂H₄). They must predict the products formed when each reacts with dihydrogen and write the balanced chemical equation, classifying dihydrogen's role as a reducing or oxidising agent.

15 min·Pairs

Real-World Connections

• The production of 'vanaspati ghee' from liquid vegetable oils, a common cooking medium in many Indian households.
• Manufacturing of nitrogenous fertilisers (like urea) from ammonia produced via the Haber process, which is vital for India's agriculture.
• The use of hydrogen as a reducing agent to extract pure metals like tungsten from their oxides for use in high-tech applications.
• In rocket fuel, liquid hydrogen is used as a high-energy propellant by organisations like ISRO.
• Development of hydrogen fuel cell buses and cars as a potential solution to urban air pollution in cities like Delhi and Mumbai.

Assessment Ideas

Exit Ticket

An exit ticket where students write the balanced chemical equation for the reaction of dihydrogen with nitrogen and list the required industrial conditions.

Quick Check

A section in the unit test with questions requiring students to explain why H₂ is a good reducing agent and to describe two of its major industrial applications with relevant chemical equations.

Quick Check

Students complete a K-W-L (Know, Want to know, Learned) chart about dihydrogen's properties and uses at the beginning and end of the topic to reflect on their learning.

Frequently Asked Questions

Why do we call it 'dihydrogen' instead of just 'hydrogen'?

'Hydrogen' refers to the element (H) on the periodic table. 'Dihydrogen' (H₂) refers to the stable, diatomic molecule that is the elemental form of hydrogen under standard conditions. It is more precise, similar to saying 'dioxygen' (O₂) or 'dinitrogen' (N₂).

If hydrogen is the most abundant element in the universe, why is it considered a future fuel and not used widely now?

On Earth, hydrogen is not found freely as H₂ gas. It is locked up in compounds like water (H₂O) and hydrocarbons. Extracting it requires a lot of energy, and storing and transporting the highly flammable H₂ gas safely and efficiently are major technological challenges that are still being solved.

What is the difference between ionic, covalent, and metallic hydrides?

Ionic hydrides are formed with s-block metals (e.g., NaH), where hydrogen acts as H⁻. Covalent hydrides are formed with p-block elements (e.g., CH₄, H₂O), involving shared electron pairs. Metallic hydrides are formed with d- and f-block metals, where hydrogen atoms occupy interstitial sites in the metal lattice.