Why can't we melt snow with a lighter? Heat transfer and hydrogen bonds

Watching kids play with snowballs brings back happy memories of our own childhood. It was such fun to drench our pals in snow and get our fair share in return. Once indoors, the snow would melt and evaporate, leaving no trace behind. As adults, this raises a puzzling question. If you try to melt a snowball with a lighter, the flame will barely affect it, leaving little more than a slight dent. A lighter’s flame is about 1,800 °F (1,000 °C) hotter than room temperature. Why, then, does such a hot flame fail at a task that warm air accomplishes with ease? The answer lies in how heat is transferred at the microscopic level.

Fig. 1. High temperature, low impact: why a lighter struggles against snow.

What does temperature mean in physics?

Temperature tells us how energetic microscopic particles are by measuring their average kinetic energy. In solids, such as snow, atoms and molecules are locked into a rigid crystal lattice, which restricts their motion. Their kinetic energy, therefore, appears mainly as vibrations about fixed positions.

In liquids, molecules gain greater freedom. Although they remain close to one another, they can rotate and move past their neighbors by continually rearranging their local surroundings. Only in gases do molecules break free entirely from this structure and move independently through space. Thus, in solids and liquids, where free motion is restricted, kinetic energy primarily manifests as vibration.

When the heat stops raising the temperature

As heat is added, these vibrations become stronger, causing the temperatureto rise. However, during a phase change from solids to liquids (and from liquids to gases), the added energy is no longer used to increase particle motion. Instead, it is diverted into weakening intermolecular bonds.

When this happens, the temperature stops rising even though heat continues to flow into the system. At the melting point, two energy pathways are available: kinetic energy, which determines temperature, and potential energy, which is stored in molecular bonds. Once the second pathway opens, it dominates. Until all bonds that can be weakened are sufficiently disrupted, the temperature remains effectively locked.

Fig. 2. Hydrogen bonds link neighboring water molecules into a flexible network that absorbs heat without raising the temperature.

Why water is special

Water molecules (H₂O) are held together by strong hydrogen bonds (Fig. 2). Hydrogen, being the smallest atom with only one proton, allows the oxygen atom of a neighboring molecule to approach very closely. This proximity makes hydrogen bonding stronger than most other intermolecular bonds.

This unusual bonding explains why water has a relatively high boiling point and a pronounced plateau at its melting point. Because temperature measures molecular motion rather than bond structure, it remains fixed until the hydrogen-bond network has been sufficiently stretched and distorted to allow the transition from solid ice to liquid water.

A flat temperature curve

If you heat ice, the temperature rises steadily below the melting point (0 °C, 32 °F). At 0 °C, the temperature curve flattens and remains flat until all the ice has melted. Only then does the temperature begin to rise again. This plateau marks a phase in which energy is absorbed without increasing temperature, because it is being used to break and reform hydrogen bonds. This behavior makes water an excellent thermal buffer. During a phase change, water acts like a heat sponge, absorbing large amounts of energy while resisting changes in temperature. 

In a snowball, the snow is already close to its melting point. You might think this would make melting easy, but it does not. Once snow reaches 0 °C, adding more heat no longer raises its temperature. Instead, the energy goes into breaking intermolecular bonds, a slow and energy-intensive process. Until these bonds are adequately weakened throughout the snowball, you won't observe the ice transforming into water under the flame of a lighter. 

The lighter’s bottleneck

When you hold a lighter to a snowball, you are not transferring temperature; you are transferring energy in the form of heat. Even though the flame from a lighter is very hot, it only touches a small part of the snow, greatly limiting how quickly energy is transferred. It may look like you're only heating that small spot, but in reality, you're trying to heat the entire snowball. The flame from the lighter is not large enough for the snowball's size. Additionally, much of the flame's energy is lost to heating the surrounding air, which rises through convection before it can penetrate the snow.

By contrast, the air inside your home comes into contact with the entire surface of the snow and transfers heat steadily over time.  While this air is much cooler than a flame, it provides a continuous supply of energy across a large surface area. Over time, this consistent energy input breaks down the entire network of hydrogen bonds, melting the snow. Heat transfer is therefore about rate, not peak temperature. Air in a room has a large thermal mass, maintains continuous contact, and delivers energy gradually over extended periods. In the end, no matter how hot a flame is, it cannot force energy into matter faster than the laws of physics allow.