You may have been wondering whether the ability to burn something is a physical or chemical property? It’s a good question and that’s because it’s often hard, at first, to separate physical changes from chemical ones. The good news is that once you know the rules of physical vs chemical, it becomes much more obvious.
Yes, flammability is a chemical property. Combustion (the act of setting something on fire) transforms one chemical into another. This fits the definition of a chemical property.
So, let’s take a look at the differences between physical and chemical properties and see how this impacts flammability and other fire-related properties such as melting and boiling points too.
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What Is A Physical Property?
A physical property of any given material is something that you can see without changing or altering the material. So, for example, gold is a shiny, yellow-colored metal. The shine and the color are physical properties.
It is easy to make it into thin sheets (gold lead) which means it is malleable (making something thinner doesn’t alter the material, it just rearranges the shape).
So, some of the typical physical properties of materials are density, color, malleability, electrical conductivity, hardness, etc.
The physical properties of a material are very useful in identifying that material though some are more useful than others.
Color isn’t a great identifier because many materials have similar colors. Density, on the other hand, is a very useful property as it varies greatly with nearly every material.
Some physical properties also denote the usefulness of a material.
What Is A Physical Change?
This is where things start to become a bit more complicated. A physical change is where the state or property of the material changes but without any accompanying change in the chemical composition of the material.
So, for example, when sugar dissolves in a cup of coffee, it doesn’t change its chemical properties, it’s still sugar (which is why it continues to taste sweet), this would be a physical change.
For another example, you might decide to magnetize a piece of iron using an electromagnetic field. When you have produced your magnetized iron, it won’t be another chemical entity, the iron will be the same metal as you started with, so this is a physical change.
In another example, imagine you have some gold as a solid but what you want is some gold powder, so you grind it down into a powder. The resulting powder is still gold, so the change is physical, not chemical.
It would be impossible for us to provide an exhaustive list of physical changes but the essence is that the material does not become another chemical during the process of change but remains the same.
What Is A Chemical Property?
The chemical properties of a material, on the other hand, refer to the potential for that material to undergo some form of chemical change.
A chemical reaction involves the sharing of electrons between substances to create “bonds” between them and it is the potential for such a reaction that is a chemical property.
Water is clearly a liquid and not hydrogen gas or oxygen gas and thus this signifies a chemical property of hydrogen when burned in the presence of oxygen.
And thus, the potential for this highly volatile reaction to explode is also considered to be a chemical property.
Sometimes, you can draw some general conclusions about groups of materials as chemical properties. For example, the vast majority of metallic elements will react when placed into an acid.
That’s a chemical property of metals.
What Is A Chemical Change?
A chemical change is thus the end product following the realization of the potential from the chemical property.
This sounds a bit more confusing than physical change but it’s not really. In most cases, it’s easy to see a change when a chemical change has occurred.
For example, when copper is added to sulfuric acid to create copper sulfate, the solution will turn blue (the color of copper sulfate) a distinct change from the clear acid and bronze-colored metal that preceded it.
Typical chemical changes include toxicity, acidity, alkalinity, reactivity, expressed heat, etc.
Chemical changes are linked to the chemical property and are often indistinguishable from each other.
The Difference Between A Physical And A Chemical Property
Physical properties can always be determined by observation, and they do not “irreversibly” change the material that has that property when it is being observed.
That is, you can find the density of gold and it won’t change gold into something else.
Chemical properties, on the other hand, require you to carry out a chemical experiment to determine whether or not the chemistry of the material was changed during the change.
Otherwise, it might be that the carbon had vaporized (a physical change, not a chemical one) and mixed with the oxygen.
Is Flammability A Chemical Property?
Yes, flammability is a chemical property.
We know this because burning something results in a chemical change (for example, creating carbon dioxide for burning carbon in oxygen or water from burning hydrogen in oxygen) that is not easily reversible.
If you wanted to prove that this was a chemical change then you would need to assay the resulting materials and demonstrate that it was made of a particular material.
However, as a rule of thumb, if something burns (that is it produces a flame and heat while there is available oxygen), you can be certain that a chemical change is taking place.
This video explains how flammability is a chemical rather than a physical property:
Examples Of Chemical Reactions Due To Flammability
Obviously, flammability is a very common chemical reaction. The most common of which is going to be either:
- Natural gas burning on your stove. The gas is burned with oxygen and it creates byproducts of water vapor and carbon dioxide (and a very small amount of carbon monoxide) this is a chemical change and it is very difficult to convert these byproducts back into natural gas.
- Gasoline burning in a car’s engine. As gasoline is a hydrocarbon similar to natural gas, this chemical reaction also causes the production of water and carbon dioxide. The heat generated by this reaction helps to drive the engine of the vehicle.
The specific reactions and their outputs may vary but if there is a chemical reaction of some kind taking place, will not.
Also read: How Long Is Spilled Gasoline Flammable For?
Is Melting Point A Chemical Property?
The melting point of a substance is a physical property. If you were to heat iron without burning it, you would change its state from solid metal to a molten one but the chemical properties of the element would not change.
And if you were to let the molten iron cool down, it would become solid again, that this change is easily reversible is a good indicator that you are dealing with a physical reaction rather than a chemical one.
Determining the melting point of a substance is usually very easy and can be done by simple observation with no need for a chemical experiment.
You simply heat the substance (and the temperature of the substance will gradually rise as you do) then at some point the substance will no longer rise in temperature, is because the heat is now being used to break melt the substance, if you note the temperature at this point – you have the melting point of your substance.
Also read: Burning vs. Melting: What’s The Difference?
Is Boiling Point A Chemical Property?
As you might expect from the melting point, the boiling point of any given material is also a physical rather than a chemical property.
The vaporization of a material does not change its chemical properties (unlike burning) and thus you know it’s a physical change.
As with melting, boiling is easy to reverse, if you allow steam to cool down, the water vapor quickly condenses to form liquid water.
If you cool it further, it will become solid water (ice) and you can see that the transition between the three phases of physical matter is easily reversible.
As with melting point, to determine the boiling point, you simply keep heating the substance until it begins to boil and the temperature ceases to rise as the energy is used to create the vapor.
Is Flammability An Extensive Or Intensive Property?
An extensive property of any material is a property that depends on the amount of material that is available at the time.
If that sounds confusing, it’s not really.
Think about a gallon of milk and a liter of milk.
The volume of milk available is an extensive property and it changes depending on the amount of milk present.
So, a gallon of milk is more than a liter is more than a cup is more than a teaspoon. Each of these measurements is a measure of an extensive property of a substance.
Conversely, an intensive property of any given material does not depend on the amount of that material available in the current state.
So, for example, temperature is an intensive property.
Look around your room at the moment, everything in it, no matter how small or how large, is at roughly the same temperature.
That’s because temperature is an intensive property.
Be careful though because heat is an extensive property (picture the difference between a dot of hot oil escaping a frying pan and your hand being submerged in a deep fat fryer, the volume of oil very much affects the amount of heat you absorb).
So, is flammability an extensive or intensive property? It’s an intensive one.
It doesn’t matter how much hydrogen you have; it will burn in oxygen.
Now, you might notice it more easily if you had a lot of hydrogen compared to a little but the fact that it will burn will not change at all.
It’s also true that by similar reasoning melting and boiling points are also intensive properties of a substance. They do not change based on how much of a substance is present.