Question

Why should it make sense that \(\mathrm{N}_{2}\) exists as a gas? Given your answer, how is it possible to make liquid nitrogen? Explain why lowering the temperature works.

Short answer

Nitrogen (N₂) exists as a gas due to its relatively inert and non-reactive properties and strong triple bond between the two nitrogen atoms. To produce liquid nitrogen, we need to cool the nitrogen gas down to reduce the kinetic energy of the molecules, allowing attractive forces between molecules to come into play. Lowering the temperature of the nitrogen gas is crucial in turning it into a liquid state, with liquid nitrogen being produced at temperatures below its boiling point of around -196°C or 77K.

Step-by-step solution

Properties of Nitrogen (N₂)

Nitrogen is a relatively inert and non-reactive element, making it a stable molecule (N₂) with a triple bond between the two nitrogen atoms. The triple bond contains a lot of energy, making the bond very strong. The strong bond makes the nitrogen molecules less likely to react with other substances and thus stay as a gas. Therefore, due to its properties, it makes sense that nitrogen exists as a gas at standard temperature and pressure.

Producing Liquid Nitrogen

To make liquid nitrogen, we need to cool the nitrogen gas down to a point where the molecules have less kinetic energy than their bond energy. By removing enough heat from the nitrogen gas, the kinetic energy of the molecules is reduced, and the gas turns into a liquid.

The Importance of Lowering the Temperature

Lowering the temperature of the nitrogen gas is the key to making liquid nitrogen because it reduces the kinetic energy of the nitrogen molecules. As the temperature decreases, the molecular motion in the nitrogen gas slows down, and attractive forces between the molecules come into play, making the molecules come closer to each other. When the temperature is lowered sufficiently, the gas will transition into a liquid state due to these attractive forces. Liquid nitrogen is produced at a temperature below its boiling point, which is about -196°C or 77K.

Key concepts

Phase Transition

When we talk about nitrogen gas \(\mathrm{N}_2\), it has a strong tendency to remain a gas at room temperature. This is due to a natural phenomenon known as a phase transition. A phase transition is a change from one state of matter to another. For nitrogen, this means transforming from a gas to a liquid.
This process involves carefully lowering the temperature so that the gas molecules lose enough energy to allow attractive forces between them to take over. By reducing the heat in a gas, its particles slow down, moving closer together. Eventually, they become packed tightly enough to become a liquid. Hence, cooling nitrogen sufficiently will result in a phase transition from a gaseous to a liquid state.
Understanding phase transition helps us know why nitrogen seems elusive as a liquid at normal temperatures, as substantial cooling is required to make it a liquid.

Kinetic Energy

Kinetic energy is a term you'll often hear when discussing gases. It refers to the energy that a particle has due to its motion. The faster a particle moves, the more kinetic energy it carries. In the case of nitrogen gas ( _{2} ), its molecules zip around quickly at room temperature, possessing significant kinetic energy.
But what happens if we cool down the nitrogen gas? By lowering the temperature, we're effectively reducing the kinetic energy of the nitrogen molecules.

• Less kinetic energy means that the molecules move slower.
• Slower molecules mean reduced movement, allowing attractive forces between them to have a greater effect.

So, when these forces manage to bring the molecules close enough, nitrogen transitions from a gas to a liquid. It's all about energy—managing motion to lead gases into liquids.

Triple Bond

Nitrogen molecules involve two nitrogen atoms bonded through a very strong triple bond. This is a key feature of nitrogen and remarkably contributes to its stability and non-reactivity. A triple bond means that three pairs of electrons are shared between the two nitrogen atoms, which tightly holds them together.
Why is this important?

• The triple bond is the reason behind nitrogen's strong resistance to change states easily.
• This bond makes nitrogen less susceptible to reacting with other substances.

In summary, the sturdy triple bond within nitrogen molecules keeps them energetically stable. It takes a reduction in temperature and kinetic energy to alter the state of the nitrogen while the triple bond ensures it remains secure and predominantly in a gaseous form.