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What is oxygen?

• Oxygen is a non-metal element that is a gas at room temperature. Its molecules contain two oxygen atoms.
• Oxygen is vital for respiration, which is the process that transfers energy from glucose to cells.
• Oxygen is necessary for burning to occur. However, burning will only happen when the mixture of fuel and oxygen is hot enough.
How is oxygen useful?
Oxygen is a non-metal element and is found naturally as a molecule. Each molecule is made up of two oxygen atoms that are strongly joined together. Oxygen has low melting and boiling points, so it is in a gas state at room temperature. A rotating model of an oxygen molecule.

Vital for life
When animals breathe in, oxygen molecules enter the lungs and pass through the lung walls into the blood. The blood carries oxygen to the cells of the body, where it takes part in a chemical reaction with glucose. This chemical reaction is called respiration.
Respiration happens all the time in every living thing: it is how the cells receive energy. If an animal or plant does not have enough oxygen, it will not be able to respire and will die.
Burning
If the temperature is high enough, many substances will burn in oxygen. When a substance burns, it reacts with oxygen: this happens in wood fires and also in car engines, which burn petrol. The chemical reaction transfers energy in order to make the engine work. The scientific word for burning is combustion.

What is nitrogen?

• Nitrogen is an element. It’s a gas at room temperature.
• Nitrogen makes up about 78% of the Earth’s atmosphere.
• Liquid nitrogen is very cold, so it is often used to freeze food.

How is nitrogen used?
Nitrogen has just one type of atom, so it is an element. It’s found naturally as a molecule, each containing two nitrogen atoms. This gives it a chemical formula of N₂. Nitrogen has a low melting and boiling point and is a gas at room temperature.
The Earth’s atmosphere is made up of 78% nitrogen. The next most common gas is oxygen, at 21%. Nitrogen isn’t very reactive, but it can react with oxygen at high temperatures, such as in car engines. These reactions make nitrogen oxides.
The boiling point of nitrogen is −196 °C, so liquid nitrogen is very cold indeed. This means liquid nitrogen is ideal for freezing food, such as vegetables, very quickly, allowing them to stay fresher for longer.

What is hydrogen?

• Hydrogen is an element; it exists naturally as a molecule. Each hydrogen molecule is made up of two hydrogen atoms.
• In petrol and diesel cars, the burning of fuel produces carbon dioxide and water. Extra carbon dioxide in the air promotes global warming.
• In hydrogen cars hydrogen reacts with oxygen in a fuel cell, making electricity to run the car. The only waste product of this process is water vapour.
• Hydrogen is one of the chemical elements that exist in nature. An element has one type of atom, and it cannot be broken down into other substances. Hydrogen exists naturally as a molecule, consisting of two hydrogen atoms. The chemical formula of hydrogen is H₂.
• Most cars burn petrol or diesel in their engines. These chemical reactions make carbon dioxide and water. Carbon dioxide is a greenhouse gas, which means too much of it can promote global warming. Global warming causes climate change, resulting in droughts, floods and extreme weather.
• Hydrogen cars help to reduce greenhouse gas emissions. They either burn hydrogen in an engine or they react both hydrogen and oxygen together in a fuel cell. Both processes produce electricity which powers an electric motor. Hydrogen cars produce one harmless exhaust gas – water vapour.
How is nitrogen used
THERMAL PROCESSES
Thermal processes for hydrogen production typically involve steam reforming, a high-temperature process in which steam reacts with a hydrocarbon fuel to produce hydrogen. Many hydrocarbon fuels can be reformed to produce hydrogen, including natural gas, diesel, renewable liquid fuels, gasified coal, or gasified biomass. Today, about 95% of all hydrogen is produced from steam reforming of natural gas.
ELECTROLYTIC PROCESSES
Water can be separated into oxygen and hydrogen through a process called electrolysis. Electrolytic processes take place in an electrolyzer, which functions much like a fuel cell in reverse—instead of using the energy of a hydrogen molecule, like a fuel cell does, an electrolyzer creates hydrogen from water molecules.
SOLAR-DRIVEN PROCESSES
Solar-driven processes use light as the agent for hydrogen production. There are a few solar-driven processes, including photobiological, photoelectrochemical, and solar thermochemical. Photobiological processes use the natural photosynthetic activity of bacteria and green algae to produce hydrogen. Photoelectrochemical processes use specialized semiconductors to separate water into hydrogen and oxygen. Solar thermochemical hydrogen production uses concentrated solar power to drive water splitting reactions often along with other species such as metal oxides.
BIOLOGICAL PROCESSES
Biological processes use microbes such as bacteria and microalgae and can produce hydrogen through biological reactions. In microbial biomass conversion, the microbes break down organic matter like biomass or wastewater to produce hydrogen, while in photobiological processes the microbes use sunlight as the energy source.

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