When we only consider what we can see happening before our eyes, we may conclude that burning a candle is a physical change.
But in reality, lighting a candle creates a chemical change that also alters the way the candle looks. As a candle burns, its hydrogen and carbon atoms combine with oxygen to create water vapor and carbon dioxide. This molecule change is a chemical reaction.
Physically, the wax melts and then becomes solid again, which describes a physical change. When burning candles you experience both types of change. Keep reading to learn more about the differences between the two.
Why Is a Burning Candle a Chemical Change?
After lighting a candle, the physical state of wax changes from solid to liquid as it melts. When it cools, what remains will solidify. Since it starts out as solid wax, becomes liquid, and then returns to solid form, these are physical changes.
But a chemical change must occur before we witness these physical changes.
Melted wax is the result of the wax surrounding the wick being transformed into carbon dioxide. Since the converted wax will never again become solid, that change is chemical.
The Difference Between Physical and Chemical Changes
We witness chemical and physical changes all the time. It simply may not be so obvious at the moment. Here are some common examples.
What Are Chemical Changes?
These reactions typically cannot be reversed. And often a new substance is formed when there’s a chemical reaction. In order for these changes to occur, a lot of light or heat energy is involved.
Cooking is one of the best examples of a chemical change. Take an egg as an example. You can use high heat to boil it and over time it transforms from a liquid to a solid. If you prepare an egg to be scrambled and they fry it, it also becomes solid.
In neither case will those eggs ever be liquid again. But a lot of heat is required to make changes to the molecular structure of the egg, otherwise, the egg will remain liquid.
What Are Physical Changes?
With physical reactions, the substance remains the same, and you can usually reverse the effects.
For instance, if you take an ice cube out of the freezer and drop it into a drinking glass, and then leave it out on the counter, it will eventually melt at room temperature.
But if you pour the liquid water from that melted cube back into the ice tray and place it back into the freezer, it will eventually harden and become a solid ice cube again.
In most cases, little heat or energy are involved in a physical state change. The room temperature is sufficient for melting ice, you don’t have to add additional heat.
How Does Burning a Candle Produce a Chemical Change?
Oxygen is required for a candle to light properly. When a candle is lit, oxygen reacts to the flame by forming carbon dioxide. This substance didn’t exist prior to lighting the candle. It’s only produced after the chemical reaction occurs.
What Happens When a Candle Is Lit?
Candle wax contains hydrogen and carbon atoms. Combined with heat from a lighter or match, the wick begins to heat the wax.
As the wax melts, it becomes the fuel that keeps the flame burning. Wax continues to travel up the wick and is released as vapor. So the heat transforms the wax into a gas.
These hydrogen and carbon atoms begin to react with oxygen. This reaction results in the formation of water vapor (hydrogen atoms combined with oxygen), and carbon dioxide (carbon atoms combined with oxygen).
In addition to the carbon dioxide, lit candles produce heat and light, two forms of energy. The gain or loss of energy is another indication of a chemical change.
The heat it produces moves in all directions. This helps to continue to melt the wax. It also adds warmth to the area around the candle.
You can read my article about the amount of light produced by candles, if interested.
Chemical changes also involve a shift in mass. You’ll notice that over time, your candle gets smaller and smaller. There’s less and less wax available to fuel the combustion. And you’ll never be able to get that wax back.
Consider lighting scented candles. Fragrance molecules are released into the air along with water vapors and any additional ingredients, like solvents, that will evaporate as the candle burns. Once the fragrance is released, you can’t retrieve it.
You experience it in a different form for as long as it makes your home smell nice. Those molecules, although too small to be visible, cling to fibers and rest on top of surfaces within your home. Over time, the scent fades.
Read more: When Candles Burn, Where does the Wax Go
Can You Break Down the Chemical Process?
I would love to break down this process of lighting a candle in more detail, but it’s beyond my understanding.
Below is a video that offers a more detailed explanation of the entire process. It’s explained by a biochemistry postdoctoral student.
If you want to learn more about all of the chemical changes, bonds created, and so forth, then you’re in for a treat.
How Does Burning a Candle Produce a Physical Change?
With physical changes, we see the mass differently, but its composition remains the same.
After wax melts, and then cools and hardens, it looks the same as it did prior to melting. The wax doesn’t change color or consistency once it becomes a solid again.
Physical changes are not permanent, that’s why they can be reversed. Once you light the candle again, it will once again melt. And once again, it will return to its original form.
When you burn a candle, it transforms from a solid, to a liquid, to a gas. During this process, new molecules are formed. Also heat and light are produced. There’s also a mass reduction as the candle gets smaller. These are all signs of a chemical change.
Once the heat source is removed from the equation by blowing out the flame, then it cools and becomes solid again. This cooling phase is part of a physical change. Because the candle returns to its original condition, even though there’s less and less wax.
There are both chemical and physical changes unfolding when burning a candle. But the burning aspect is chemical. Although melting and solidifying of the wax is a physical reaction, these visible changes wouldn’t be possible without all of the chemical reactions.
Thus, I’m going to conclude that burning a candle is a chemical change.