Why sugar dissolves faster in hot water than in cold water?

Prepare an ice-cold juice and add sugar, and you would see sugar crystals at the bottom of the glass. However, this won’t be the same when you make a cup of hot coffee, wherein sugar dissolves remarkably faster. But why? What’s the reason behind sugar breaking down more quickly in hot water than in cold water?

First, let’s know about sugar. Sugar is actually sucrose, which is composed of carbon (12 atoms), hydrogen (22 atoms), and oxygen (11 atoms). Same with other compounds produced from combining these three elements, sugar is also a carbohydrate. It is made naturally in plants. You can find it in fruits, vegetables, and even nuts. Sugarbeets and sugar cane are where sugar is most abundant. In fact, the former accounts for about 55% of sugar production in the United States, while the latter make up the remaining 45%.

But, sugar is also two simpler types of sugars joined together, glucose and fructose. In cooking, adding small amounts of acid, such as cream of tartar, or citric juice, are enough to crack up sugar into these two simpler components.

Now, why does hot water dissolves faster in hot water? Well, hot water has water molecules moving at an increased rate of speed and better kinetic energy. With that, sugar breaks down more quickly the increased vibration. As the water molecules tend to be more ‘mobile’ and move significantly faster, it forces the sucrose molecules to move quicker as well.

Then, with sucrose molecules forced to move faster, the less is it able to hold its components. The bonds keeping the sucrose molecules together becomes weaker, allowing water molecules to step in and link themselves to the molecules of sugar. Thus, it also produces energy, tugging sucrose molecules from each other. With that, the dissolution of sugar happens faster compared to what it would be in cold water.

So, if you put a sugar cube to a glass of cold water, and another one to a cup of warm water, you will notice that sugar break downs quickly in the latter. Putting it simply implies that sugar molecules move faster and interact greater in higher temperatures as it has higher kinetic energy that forces it to do so.

However, try touching the cup of water as the sugar breaks down. You may observe that the temperature of the cup seems to do down. That is because dissolving sugar also uses energy from the immediate environment to do the process. Such occurrence is regarded as endothermic change, wherein heat is absorbed from the surroundings to facilitate the reaction, decreasing the temperature of the environment. Melting ice cubes, salts, or evaporating water are other samples of endothermic processes.

But while sugar dissolves pretty faster in hot water, you would not be able to dissolve a limitless amount of sugar is a specific volume of water. When too much sugar is added, the water solution with become saturated. In such a case, part of the sugar amount will melt, while the rest will rest at the bottom of the container in a solid state. When that happens, you may opt to transfer the solution into a bigger container and add more water to dissolve the sugar.

Moreover, you could also stir the solution. It can aid in dispersing the sucrose molecules in the water, creating more surface area, and accelerating the dissolution process. The motion increases the high kinetic energy present in hot water, allowing sugar to dissolve more quickly.

More Readings:

Sugar (Wikipedia)

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