Did you know that the boiling point of a liquid isn’t always the same? It actually changes depending on the pressure around it. For example, water usually boils at 100 degrees Celsius, but that’s only true when the pressure is at 1 atmosphere, which is the normal air pressure at sea level. If the pressure is lower, like on a mountain or in a vacuum, water can boil at lower temperatures, even at room temperature!
Here’s something cool: when water boils at room temperature, it actually gets colder. This happens because the fastest water molecules, which have the most energy, escape first. The slower, less energetic molecules are left behind, making the water cooler. This is like a natural way to refrigerate the water!
You’ve probably heard of liquid nitrogen, but did you know nitrogen can also become a solid? By lowering the pressure around liquid nitrogen, we can make the fastest nitrogen molecules escape, which cools it down even more until it freezes into a solid.
To see how cold liquid nitrogen is, we can use a tool called a thermocouple. It measures the temperature and shows that liquid nitrogen is about -196 degrees Celsius. When we remove the air from around it, the nitrogen boils, and the temperature drops even further, getting close to -200 degrees Celsius!
As the temperature keeps dropping, solid nitrogen starts to form. The solid nitrogen, or ice, gets pulled up because of the lower pressure above it, while the pressure below stays higher since the vacuum pump can’t reach there.
Once we have solid nitrogen, we can do something even more amazing. By pouring it onto a water bath, the extreme cold causes carbon dioxide from the air to freeze, forming solid carbon dioxide, which we call dry ice. This happens right on the surface of the water!
This journey into boiling points, pressure, and temperature shows us how substances behave in different conditions. By changing these factors, we can see some amazing things, like making solid nitrogen and dry ice. It’s a great way to understand important scientific ideas and see them in action!
Conduct a simple experiment to observe how water boils at different temperatures depending on the altitude. Use a pressure cooker or a vacuum pump to simulate high-altitude conditions. Measure the boiling point of water and compare it to the standard boiling point at sea level. Record your observations and explain why the boiling point changes with pressure.
Use an online simulation to explore how pressure affects the boiling point of various liquids. Adjust the pressure settings and observe the changes in boiling points. Take notes on how each liquid behaves under different pressures and discuss your findings with your classmates.
In a supervised setting, work in groups to create dry ice using solid nitrogen. Observe the process of carbon dioxide freezing and forming dry ice. Discuss the science behind this transformation and how pressure and temperature play a role in the formation of dry ice.
Research the properties and uses of liquid nitrogen. Create a presentation to share with the class, explaining how liquid nitrogen is used in various industries and scientific experiments. Include information on how pressure and temperature affect its state and applications.
Solve math problems related to pressure changes and their effects on boiling points. For example, calculate the pressure needed to boil water at $25^circ$C. Use the formula $$P = P_0 times e^{left(frac{-L}{R}right)left(frac{1}{T_1} – frac{1}{T_0}right)}$$ where $P_0$ is the standard pressure, $L$ is the latent heat, $R$ is the gas constant, and $T_1$ and $T_0$ are the temperatures in Kelvin.
Boiling – The process where a liquid changes to a gas at its boiling point, which is the temperature at which its vapor pressure equals the external pressure. – When water reaches a temperature of $100^circ text{C}$ at sea level, it begins boiling and turns into steam.
Pressure – The force exerted per unit area on the surface of an object. – The pressure inside a balloon increases as more air molecules are added, causing it to expand.
Temperature – A measure of the average kinetic energy of the particles in a substance. – As the temperature of the ice increases, it begins to melt into water.
Nitrogen – A colorless, odorless gas that makes up about 78% of the Earth’s atmosphere and is essential for life. – Nitrogen is used in fertilizers to help plants grow by providing essential nutrients.
Solid – A state of matter characterized by particles arranged in a fixed structure, giving it a definite shape and volume. – Ice is a solid form of water, where the molecules are tightly packed in a crystalline structure.
Liquid – A state of matter with a definite volume but no fixed shape, allowing it to flow and take the shape of its container. – Water is a liquid at room temperature, allowing it to be poured from one container to another.
Molecules – Groups of two or more atoms bonded together, representing the smallest fundamental unit of a chemical compound. – Water molecules consist of two hydrogen atoms bonded to one oxygen atom, represented by the formula $H_2O$.
Energy – The capacity to do work or cause change, often manifesting as heat, light, or motion. – When you heat water, energy is transferred to the molecules, increasing their motion and eventually causing the water to boil.
Ice – The solid form of water, typically formed when water freezes at $0^circ text{C}$ or below. – Ice floats on water because it is less dense than liquid water, due to the arrangement of its molecules.
Carbon Dioxide – A colorless, odorless gas produced by burning carbon and organic compounds and by respiration. – Plants use carbon dioxide during photosynthesis to produce oxygen and glucose.
