Why does adding salt to ice lower the temperature?

The other day, I read in a scientific magazine that the temperature of ice cubes drops dramatically when salt is added, and I think this is a "paradox". I pondered on my own: table salt itself is not cold, how can the temperature drop when ice cubes are added with salt?

I was dismissive of this, and in order to break this "rumor", I deliberately did an experiment to verify it. I prepared the tools for the experiment: a speed-reading thermometer, a glass, some ice cubes, and table salt.

The experiment began, my mother asked me to wash the cup first, and then pour in a lot of ice, at this time my hand holding the cup was like ice, I quickly put the cup on the table, put the thermometer prepared in advance into the bottom of the ice, and measured the temperature of the ice. Then we stared at the temperature tray. The indicator hand of the "boom" temperature disc moves backwards very quickly5 ....0℃…The -2 pointer finally stopped at -4.

At this time, in order to find out whether this is a "rumor", I carefully looked at the thermometer and added salt to the ice from time to time. "Wow"! A miracle really happened, and the indicator needle, which had just breathed a sigh of relief, suddenly plummeted to -5....-8℃…The -11 mark was broken one by one, and finally the indicator needle finally came to a slow stop at -14.

I was stunned, the temperature difference was 10 before and after, and there is no reproach that this "rumor" is true! It was also found that the magnitude of the temperature drop was related to the amount of salt added, and the rate of decline was very fast. At this point, I'm still confused, but why?

So I asked the computer master to help explain: whether it is the dissolution of salt or the melting of ice cubes, you have to absorb a certain amount of heat from the surroundings, and after obtaining the heat, your temperature rises before it changes into a liquid state. In other words, if you mix ice cubes with table salt, the ice cubes themselves will always melt a little, and it takes the heat around them to melt, so the surroundings will be cold.

The melted ice turns into water, and the salt dissolves in the water, and the salt needs to absorb the surrounding heat. This process is repeated to melt the ice cubes and dissolve the salt, and with each change, the surrounding heat is lost, and in this way, the temperature of the ice cubes drops sharply when salt is added. Seeing this, I suddenly remembered a sentence from the mouths of the old people:

Snow does not cool and snow is cold", seems to be explained in today's experiment. When it snows in winter, people don't feel cold, but when the snow melts, it feels much colder and wetter. Snow is the condensation of water in the air from liquid to solid, and condensation needs to dissipate heat, so the temperature is about the same as usual, and it doesn't feel too cold; Melting snow is the evaporation of solid into liquid or gas, dissolving, melting, evaporating and sublimation all need to absorb heat, so it feels cold and damp; Compared to the two, it is of course colder when it snows than when it snows.

Through this experiment, I have learned that science is an honest science, and it must not be false. The natural world is endless, waiting for us to discover, observe, explore, and innovate. <>

Ice and salt, when melted, draw heat from their surroundings, that is, it is this endothermic effect of them that causes the temperature to drop. In order for the ice to melt, it is necessary to have heat, and as the ice melts, it constantly absorbs the heat from its surroundings. Therefore, next to the ice, people will feel cool.

Also, if salt is added to the water melted by the ice, the temperature will be lowered, because the salt will also absorb the surrounding heat when it melts. In addition to salt, there are many substances that have such endothermic properties, such as sea waves.

Pharmaceuticals used to wash photographs), which have a particularly strong endothermic effect. Of course, the endothermic effects of various substances are different. If ice and salt are mixed together in a ratio of 3 to 1, it becomes what is called a refrigerant, which can reduce the temperature to <>

If salt is added to the ice, the ice will melt faster. Because salt melts ice. The principle is:

The composition of salt is sodium chloride NaCl, and the composition of snow is water. Sodium chloride is a chemical substance that is extremely soluble in water, and sodium chloride is dissolved in water to form an aqueous solution of sodium chloride, which contains sodium ions and chloride ions. When water is about to freeze, when there are sodium ions and potassium ions, chloride ions and sodium ions will destroy the crystalline network structure of water, so that the water cannot freeze.

Moreover, salt can lower the melting point of ice, so that it does not freeze at low temperatures. The freezing point of brine is usually around -18 degrees, and adding a certain amount of salt to the ice can melt ice above -18 degrees. When water is converted from a solid to a liquid state, it needs to absorb heat from the surrounding environment to achieve the purpose of cooling.

The 3:1 ratio of crushed ice to salt can usually be cooled to -18 degrees, and theoretically -20 degrees. <>

Adding salt to the ice does not lower the temperature, but lowers the freezing point of the brine, so that the brine does not solidify easily and melts faster.

Because salt can absorb heat, adding it to ice water will cause the temperature to become lower and lower, which is a typical physical phenomenon.

Because the melting of salt absorbs heat, the melting process of ice absorbs energy, causing the surrounding temperature to drop sharply, so the temperature will be lower.

This is because the freezing point is lowered, which is why this happens, and people feel the temperature drop.

Ice and salt, when melted, draw heat from their surroundings, that is, it is this endothermic effect of them that causes the temperature to drop, and in order for the ice to melt, it is necessary to have heat.

As the ice melts, it constantly absorbs the heat from its surroundings. As a result, people will feel cool next to the ice, and if salt is added to the water melted by the ice, the temperature will be lowered, because the salt will absorb the surrounding heat as it melts.

The O-O nucleus spacing of the closest water molecule is about 109°, which is very close to the 109°28 bond angle of an ideal tetrahedron.

However, the O-O spacing of each water molecule that is only adjacent and not directly bound is much larger, and the farthest one should be reached. Each water molecule can combine with 4 other water molecules to form a tetrahedral structure, so the coordination number of the water molecule is 4.

Salt can melt ice so the temperature is lowered.

Its advantages are low cost, good snow melting effect, suitable for use in cold areas, the amount used is 1 2-1 5 of the existing snow remover, and the freezing point of salt water is lower than that of pure water. To melt the accumulated ice and snow in an environment where the temperature is lower than zero, the common method is to add salt, so that the salty snow water is easier to melt without freezing again, and the interface in contact with it can continuously melt the ice and snow, and the amount of salt is sufficient, so that the accumulated ice and snow can slowly melt into water is to increase the condensation nucleus, which is related to the principle of artificial rainfall, when ice and salt melt, absorb heat from the surroundings, that is, it is through this absorption that the temperature drops.

In order for the ice to melt, there must be heat, and in the process of ice melting, it is constantly absorbing heat from its surroundings. As a result, people will feel cool next to the ice. Also, if salt is added to the water of melted ice, the temperature drops even lower because the salt absorbs the surrounding heat as it melts.

If ice is mixed with salt in a three-to-one ratio, it becomes a so-called refrigerant, which can bring the temperature down to. The dissolution of salt, or the melting of ice, absorbs a certain amount of heat from the surroundings, and when heated, their temperature rises and they become liquid.

In other words, when you mix ice and salt together, the ice will melt a little bit and it needs the heat around it to melt, so it gets colder. The melted ice turns into water, while the salt dissolves in the water. Salt also needs to absorb the heat from the surroundings.

This repeats the melting process of ice and salt, and with each change, the heat around the ice is lost, so when the salt is added to the ice, the temperature drops.

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Ice is water, and when ice and salt react, the temperature rises. Therefore, under normal circumstances, salt will be sprinkled on the road surface to melt after it freezes.

The melting of salt will absorb the heat of the surroundings, and the melting of ice will also absorb the heat of the surroundings, so the temperature will decrease.

The principle is that when ice and salt melt, they will absorb heat from their surroundings, because the activity of sodium ions is very high, and they will continue to move, which will absorb the heat in the ice, causing the ice to melt.

The main reason is that if the temperature is too low, it will react with the edible salt, which will cause the temperature to drop again.

It is reasonable that ice and salt receive heat from all over the world at the moment of melting, because the activity of sodium ions is very high, and the constant activity receives the heat in the ice, causing the ice to melt.

<>, because when salt is added to water, it will reduce the vapor pressure of the water, thereby reducing its chemical potential, so the melting point is reduced, in simple terms, it is the melting point, the vapor pressure of the water vapor of ice is equal to the vapor pressure of the water vapor of the water. When the vapor pressure of these two is affected, the melting point must be changed again in order to achieve equality again. The addition of salt is to change this melting point to a lower temperature, and the practical effect is that the melting point is reduced.

Salt does not allow the ice to cool down.

However, salt can reduce the freezing point of a mixture of brine + ice water.

That is, the freezing point of the solution after mixing salt and water will be reduced.

In general, the freezing point of water is 0

With the addition of salt, the freezing point of the brine can be reduced to below zero.

Many buildings use frozen brine for air conditioning, and many factories need low-temperature environments.

However, table salt dissolved in water, even if it is endothermic, is not enough to freeze the water.

Anyway, the actual mechanism should be like this.

There is ice in the beaker, and then put in the salt, the test will lower the freezing point, so there will be a large amount of ice melting into water, ice melting into water is a very endothermic reaction, if we do not consider the effect of the freezing point change and the influence of room temperature, we can approximate that how much ice in the beaker becomes water, how much water in the test tube becomes ice (the actual loss is a lot).

Because the freezing point is lowered, as long as there is ice and water in the beaker, the problem of the ice-water mixture must be below 0 degrees, which means that the heat transfer will continue before the test tube is completely frozen.

When salt is placed in a beaker filled with ice, the salt will drop the freezing point of the water, causing the ice to melt. The melting of ice requires the absorption of heat, and inside the test tube is water at room temperature, which is much higher than the temperature of the beaker. In this way, the heat is continuously transferred from the tube to the beaker.

The transfer of heat will only stop when the temperature of the beaker and the tube is the same, so that as long as enough ice is present in the beaker, the water in the tube will become ice.

It is common knowledge in physics that salt water has a lower freezing point than ordinary water.

For example, sea water does not freeze easily, for example, in winter, salt is sprinkled to prevent the road from freezing.

The specific mechanism of this has nothing to do with chemistry, it is basically the category of molecular kinematics, and the specific mechanism may be that sodium ions are mixed into water molecules, and chloride ions change the intensity of molecular thermal motion.