Question about whether hot or cold seems elementary, but it baffles many people, including scientists. Intuitively, it seems that a cold liquid should turn to ice sooner, since it has less temperature difference to overcome. However, physics is full of surprises, and under certain conditions, hot water can outpace cold water in the race for crystallization. which water will freeze faster in the refrigerator - hot or cold - seems elementary, but it baffles many people, including scientists. Intuitively, it seems that a cold liquid should turn to ice sooner, since it has less temperature difference to overcome. However, physics is full of surprises, and under certain conditions, hot water can outpace cold water in the race for crystallization.
This phenomenon was named Mpemba effect and was officially recognized by science in the second half of the 20th century, although it has been known since the time of Aristotle. At home, using a regular refrigerator or freezer, you can conduct this experiment yourself, but the result will depend on many factors: the material of the container, the purity of the water, the level of humidity and even the location of the form in the freezer.
In this article We will analyze in detail the physical processes behind the freezing of water and answer the question of which liquid is best to freeze to obtain ice for cocktails. We will look at how water molecules they behave at different temperatures and why sometimes “hot” is faster than “cold”.
Physical paradox: The Mpemba effect
Paradox named after the Tanzanian schoolboy Erasto Mpemba, is that under certain conditions, hot water freezes faster than cold water. This contradicts classical thermodynamics, if we consider the process in a simplified way. However, upon closer examination, it turns out that the rate of freezing is affected by evaporation, scale formation and hypothermia.
When you put hot water in freezer active evaporation begins. Since evaporation is an endothermic process, it removes a significant amount of heat from the remaining liquid. As a result, the mass of water decreases, and it becomes easier to cool a smaller volume. In addition, hot water contains fewer dissolved gases, which also changes its properties.
⚠️ Attention: Do not place containers with boiling water in the refrigerator! This can lead to spoilage of other products, the formation of ice on the walls and increased load on the compressor. Allow the water to cool to at least 60-70 degrees.
Scientists are still arguing about the exact mechanism of this phenomenon, but most agree that convection currents play a key role. In hot water they are more intense, which contributes to a more uniform and rapid cooling of the entire volume of liquid compared to static cold water.
Comparison of cold and hot water: experiment
If you decide to conduct the experiment at home, you will need two identical containers, a thermometer and a timer. It is important to use water from a single source to eliminate the influence of impurities. Results may vary depending on the initial temperature and volume.
Cold water (for example, from a tap, around +15°C) begins the crystallization process immediately, since it has a smaller temperature difference to overcome. However, it may experience the effect of hypothermia, when the liquid drops below 0°C, but remains liquid until shaken.
Hot water (about +80°C) first spends time cooling to the temperature of cold water, but due to the factors described above (evaporation, convection) it can “catch up” and overtake the cold sample. In a regular household freezer, the difference can be from 10 to 30 minutes in favor of hot water, if conditions are ideal.
It is worth considering that freezing rate depends on the thermal conductivity of the container. Plastic cups will slow down the process, while metal molds or thin glass will provide better heat transfer. The contact of the bottom of the container with the freezer shelf is also important.
The influence of impurities and type of water on freezing
Not all water is the same. The chemical composition of the liquid directly affects the crystallization temperature. Distilled water, devoid of salts and minerals, behaves differently than tap or mineral water.
Tap water contains calcium and magnesium salts, which precipitate when heated (scale). When you boil water, the concentration of these salts changes, which can slightly raise the freezing point of the remaining liquid compared to unboiled liquid. However, the presence of dissolved gases in cold water can, on the contrary, hinder the formation of ice crystals.
Distilled water often exhibits severe hypothermia. There are no crystallization centers in it, so the freezing process can begin suddenly and instantly cover the entire volume.
For domestic purposes, it is best to use filtered water. It is devoid of chlorine and large impurities, but retains natural mineralization, which allows the ice to be transparent and tasty. Boiled water is also good, since it contains less hardness salts, which makes the ice less cloudy.
Technical aspects of the operation of the freezer
The rate of freezing of water in the refrigerator depends not only on the water itself, but also on the capabilities freezer compartment. Modern models with a system No Frost provide circulation of cold air, which speeds up the process compared to the static cold in older models.
Temperature also plays a role. If the freezer is set to -18°C, the process will proceed as usual. However, the Super Freeze function, which temporarily lowers the temperature to -24°C or -30°C, will significantly speed up ice formation regardless of the initial water temperature.
☑️ Proper freezing of water
It is important to remember the load on the compressor. If you put in several liters of hot water at once, the refrigerator will work harder, trying to compensate for the heat. This may lead to a temporary increase in temperature in the main chamber, which is dangerous for the products stored there.
⚠️ Attention: A sharp increase in temperature in the main chamber of the refrigerator due to loading hot items can lead to defrosting of meat or spoilage of dairy products. Check the temperature after such experiments.
Table: Comparison of freezing characteristics
For clarity, let’s compare the main parameters that affect the process, depending on the type of water and conditions.
| Parameter | Cold water (+15°C) | Hot water (+80°C) | Distilled water |
|---|---|---|---|
| Time before crystallization begins | Fast (30-40 min) | Long (60+ min) | Very long-term (hypothermia) |
| Risk of Mpemba effect | None | High (may freeze faster) | Low |
| Ice transparency | Medium (gas bubbles) | High (gases removed) | Ideal |
| Impact on the refrigerator | Minimum | High load | Minimum |
As can be seen from the table, hot water has advantages in the quality of the resulting ice (it is more transparent), but requires more time at the initial stage. Cold water is more reliable in terms of predictable timing, but ice can be cloudy due to air bubbles.
The choice of strategy depends on your goal: if you need to get some ice quickly and have a powerful freezer, you can try hot water. If the stability and safety of the equipment is important, it is better to use cold one.
Practical tips for quick freezing
To speed up the process of making ice at home, you can use several proven methods. They are based on the laws of physics and will help you save time.
First, use shapes with a large surface area. The thinner the layer of water, the faster it will give off heat. Flat containers freeze faster than tall, narrow glasses.
The metal tray works as a heat sink, speeding up the freezing process by 15-20% compared to placing the mold directly on a plastic shelf.
Secondly, ensure good air circulation. Do not place molds close to walls or other food. Cold air should flow freely around the container from all sides.
Using water at room temperature is the “golden mean” between speed, ice quality and the safety of household appliances.
You can also add a pinch of salt to the water if the ice is not intended for food, but for cooling drinks (for example, in a bag). Salt lowers the freezing point, but when mixed with ice it creates a more aggressive cooling environment. For edible ice, do not add salt.
Frequently asked questions (FAQ)
Is it true that hot water always freezes faster?
No, this is not always the case. The Mpemba effect is observed only under certain conditions (shape of container, material, initial temperatures). In most everyday situations, cold water will freeze earlier or at the same time, since it needs to overcome a shorter temperature path.
Is it possible to put boiling water in a No Frost freezer?
Technically it is possible, but not recommended. Steam from boiling water will quickly turn into frost on the evaporator and fans, which will require more frequent defrosting of the system (if it is not automatic) and will increase energy consumption.
Why is the ice in the refrigerator cloudy, but in the bar clear?
Turbidity is caused by dissolved gases and impurities that are pushed out when freezing and form bubbles. In bars, they use special machines with water circulation or freeze water in layers, displacing bubbles into the center, which is then removed.
Does the mold material affect the freezing rate?
Yes, significantly. Metal molds conduct heat better than plastic or silicone. In a metal form, water will freeze faster, but it may also be more difficult to remove ice from it without damaging the coating.
How long does it take for water to freeze in the freezer?
In a standard freezer at a temperature of -18°C, a 200 ml glass of water will freeze in about 1.5–2 hours. Complete freezing of a large volume (for example, 1 liter) can take 3–4 hours.