How much do you adore electricity? It provides power to your beloved electronic devices. It has the ability to cool you down during the summer and warm you up in the winter. It illuminates your path when the Sun sets.
However, when a thunderstorm strikes and brings lightning and thunder, you might lose electricity if vital electrical components, such as transformers, are struck by lightning. In such a situation, what do you do?
You could sit in the darkness and patiently wait for the lights to come back on, but that can be quite dull. Instead, you would probably grab a flashlight to continue reading your favorite book. Can you imagine what it was like for children in the past, before the advent of electricity? What would it have been like to read by the soft glow of candlelight every evening?
If you have ever observed a burning candle, you might have noticed something intriguing. The part of the candle that you light, known as the wick, burns. But what about the rest of the candle? The wax melts. So, why do some substances burn while others melt?
Although it may appear that burning and melting are two sides of the same coin, they are actually distinct processes. Different materials react differently when exposed to heat.
Melting is a physical process that involves the transition of a substance from its solid state to its liquid state. On the other hand, burning is a chemical process that entails the breakdown of a substance and its transformation into different substances.
For instance, when an ice cube melts, it changes from a solid cube of ice into liquid water. However, it is still the same substance: water. On the contrary, when wood burns, it undergoes a transformation from its original composition (cellulose, lignin, water, etc.) into new substances (charcoal, methanol, carbon dioxide, etc.).
Substances that burn instead of melt have combustion temperatures that are lower than their melting points. Before they have a chance to reach a temperature high enough to melt, they react with oxygen in the atmosphere and undergo combustion or burning.
This is the case with wood. You have probably observed that wood does not melt when exposed to heat. Instead, wood reacts with oxygen in the air and burns, resulting in the formation of charcoal, ash, and other substances.
If you have ever attempted to turn charcoal, ash, and the other remnants left behind from a campfire back into wood, you would know that it is not possible. This is because a chemical change has occurred. However, if you have liquid water, you can cool it down to its freezing point and cause it to undergo a phase transition back into a solid state.
Give It a Try
Are you eager to learn more about heat? Make sure to explore the following activities with a friend or family member:
- With the assistance of an adult friend or family member, locate a candle and a lighter. Ignite the wick of the candle and observe it for a period of time. How do the candle wick and the candle wax differ? Isn’t it fascinating to witness burning and melting occurring simultaneously right beside each other?
- Under the guidance of an adult friend or family member, initiate a fire in the fireplace. If you don’t have a fireplace, you can always start a fire outdoors in a fire pit. You could even visit a park and construct a campfire! Observe the wood attentively as it starts to burn. How rapidly does it transform into ash? What do you imagine wood would appear like if it had the ability to melt?
- To gain further knowledge about physical phase transitions, acquire a few ice cubes from the freezer. Place them in a bowl and watch as they commence melting. If possible, utilize a hair dryer to apply more heat and expedite the melting process. Once all the frozen water has converted into liquid water, transfer it to a pan and heat it on the stove until it reaches boiling point. Keep observing it as it evaporates into a gas. Aren’t you grateful that water can’t be ignited?
Sources of Wonder
1. Why do some things burn while others melt?
Some things burn while others melt because of their chemical composition and the way they react to heat. When a substance burns, it undergoes a chemical reaction with oxygen, releasing heat and light. Combustible materials, such as wood or paper, contain carbon and hydrogen atoms that can react with oxygen to produce carbon dioxide and water vapor. On the other hand, when a substance melts, it changes from a solid to a liquid state due to an increase in temperature. This occurs when the substance’s molecular structure is disrupted, allowing the particles to move more freely. The melting point of a substance depends on its intermolecular forces and the strength of its molecular bonds.
2. What causes a substance to burn?
A substance burns when it undergoes a chemical reaction with oxygen in the presence of heat. This process is known as combustion. Combustion occurs when the substance’s atoms or molecules combine with oxygen atoms to form new compounds. The release of heat and light energy is a result of this chemical reaction. The ability of a substance to burn depends on its chemical composition and its ability to react with oxygen. Substances that contain carbon and hydrogen atoms, such as organic materials, are typically combustible and can burn in the presence of a sufficient amount of oxygen and heat.
3. Why do some substances melt instead of burning?
Substances melt instead of burning when they are exposed to heat. Melting occurs when a solid substance is heated to a temperature above its melting point, causing its molecular structure to break down. Unlike combustion, the melting process does not involve a chemical reaction with oxygen. Instead, the increase in temperature causes the particles in the substance to gain enough energy to overcome the intermolecular forces holding them together. This allows the substance to transition from a solid to a liquid state. The melting point of a substance is determined by its molecular structure and the strength of its intermolecular forces. Substances with stronger intermolecular forces generally have higher melting points.
4. Can substances both burn and melt?
Yes, substances can both burn and melt, but these processes are distinct from each other. Burning involves a chemical reaction with oxygen, while melting is a physical change caused by an increase in temperature. Some substances, such as candle wax or butter, can both melt and burn. When these substances are heated, they initially melt and transform into a liquid state. If the temperature continues to rise and there is sufficient oxygen present, the melted substance can undergo combustion and burn. However, not all substances can burn, as their chemical composition may not allow for a reaction with oxygen, even at high temperatures.
5. What factors determine whether a substance will burn or melt?
Several factors determine whether a substance will burn or melt. The chemical composition of the substance plays a crucial role. Combustible substances contain elements like carbon and hydrogen that can react with oxygen to produce combustion. In contrast, substances that do not contain these elements or have strong molecular bonds are less likely to burn. The strength of intermolecular forces also affects whether a substance will melt or not. Substances with weaker intermolecular forces are more likely to melt at lower temperatures, while those with stronger forces require higher temperatures to melt. Additionally, the presence of oxygen and the amount of heat applied are key factors in determining whether a substance will ignite and burn or simply melt.
6. Can a substance burn without melting?
Yes, a substance can burn without melting. Combustion is a chemical reaction that occurs when a substance reacts with oxygen, releasing heat and light. The ability to burn is determined by the chemical composition of the substance and its ability to react with oxygen. Some substances, like wood or paper, can burn without melting because their molecular structure allows for a chemical reaction with oxygen. Melting, on the other hand, is a physical change that occurs when a solid substance is heated to its melting point and transitions into a liquid state. It does not involve a chemical reaction with oxygen. Therefore, a substance can undergo combustion and burn without melting if it has the necessary chemical properties to react with oxygen.