Question

Water is \(88.88\) percent oxygen by mass. Oxygen is exactly what a fre needs to grow brighter and stronger. So why doesn't a fire grow brighter and stronger when water is added to it?

Short answer

Water contains oxygen, but it's chemically bound and cannot support combustion, extinguishing fire instead.

Step-by-step solution

Understanding the Composition of Water

Water is composed of two hydrogen atoms and one oxygen atom, making its chemical formula \(H_2O\). Although oxygen makes up 88.88% of the mass of water, it is chemically bonded to hydrogen.

Analyzing Water’s Role in Combustion

Oxygen is vital for combustion as it supports the chemical reactions that produce fire. However, in water, oxygen is locked in a stable compound with hydrogen, preventing it from participating in combustion.

Examining the Effects of Water on Fire

When water is poured on a fire, it absorbs heat and cools the combustible material below its ignition point, thus extinguishing the fire. The presence of hydrogen also contributes since, when vaporized, it displaces oxygen around the fire.

Concluding Explanation

Though water contains oxygen, it is in a form that cannot support combustion. Instead, water extinguishes fire due to its ability to absorb heat and decrease the surrounding oxygen concentration.

Key concepts

Chemical Bonding

Chemical bonding refers to the attraction between atoms that allows the formation of chemical substances containing two or more atoms. In water, each oxygen atom forms chemical bonds with two hydrogen atoms. These bonds are particularly strong and stable, known as covalent bonds, which involve the sharing of electron pairs between atoms.

• Formation of Chemical Bonds: The hydrogen and oxygen in water share electrons, forming a molecule with the formula \(H_2O\).
• Why Chemical Bonds Matter: These bonds absorb energy, making water a stable compound that doesn't easily break down to release individual oxygen atoms.

The stability of these bonds means that oxygen is not readily available to support combustion, explaining why water, despite being rich in oxygen content, cannot fuel a fire. This chemical bondage keeps oxygen "locked" away, preventing its participation in any reactions, including combustion.

Water Composition

Water is a simple yet fascinating compound made up of two hydrogen atoms covalently bonded to one oxygen atom, often referred to by its chemical formula, \(H_2O\). In terms of mass, oxygen constitutes 88.88% of water because it is significantly heavier than hydrogen.

• Mass versus Composition: While oxygen takes up most of the mass, the molecule's properties are defined by the chemical bonds and spatial arrangement.
• Stable Compound: Water's stable nature as a compound makes it unlikely to decompose under standard conditions, unlike the free oxygen required for combustion.

Understanding the composition of water helps explain why it behaves differently from its elemental components. The combined hydrogen and oxygen form water, which acts entirely differently than either element on its own, especially regarding fire and heat interactions.

Oxygen Role

Oxygen plays a crucial role in combustion, a chemical process that typically involves the rapid combination of oxygen with another substance, resulting in the release of heat and light. It's why a fire burns brighter and extends as long as there is a steady supply of oxygen.

• Combustion and Oxygen: Free oxygen molecules boost the combustion process, allowing fires to sustain and grow.
• When Bound in Water: In water, oxygen is not in a free state but bonded, which means it does not contribute to combustion.

Therefore, water hinders rather than helps a fire when applied because the oxygen it contains is not available for the oxidizing reactions necessary to fuel flame continuation.

Fire Extinguishing Mechanism

Extinguishing a fire involves removing or reducing one of the three components necessary for combustion: fuel, heat, and oxygen. Water serves as an efficient fire extinguishing agent primarily due to its ability to absorb heat and vaporize.

• Heat Absorption: Water absorbs heat from the fire, cooling the burning material below its ignition point, which is necessary to sustain the fire.
• Oxygen Displacement: As water evaporates, it creates steam that displaces oxygen around the fire, further suffocating the flames.

The combination of cooling the combustible material and reducing available oxygen makes water exceptionally effective at putting out small to medium-scale fires, even though it contains oxygen itself. The result is a comprehensive approach to fire suppression, leveraging water's physical properties to disrupt the combustion process.