How to convert kj/kg.k to kj/kg.c?

Heat causes molecules to move, and this movement is called molecular diffusion. The greater the temperature in a substance — the more the molecules move, and the higher the rate of diffusion. The movement of molecules also depends on a range of other factors, such as pressure, the viscosity of the substance, its concentration, resistance to diffusion, the distance that a molecule travels in order for the diffusion to occur, and the mass of a molecule. For example, if we compare water and honey, we will notice that with all other conditions such as pressure and temperature being equal, diffusion happens faster in water, because its viscosity is lower than that of honey.

The movement of molecules requires energy, and to make molecules move faster, more energy is required. If we want to increase diffusion by raising the temperature of a substance, for example by heating it, we will have to generate energy to produce this heat. We can burn some gas, coal, or wood, for this purpose. If we heat up several different substances with the same amount of energy, some substances may warm up at a faster rate than others, because of the factors above that affect their diffusion rate. To represent these properties of materials and substances, we use the terms specific heat capacity and heat capacity.

Specific heat capacity represents how much energy (or heat) is needed to change the temperature of an object of a given mass by a given value. This is different from heat capacity, which measures the amount of energy needed to change the temperature of an object or matter by a given value. Mass is not considered when calculating heat capacity. Heat capacity and specific heat capacity are only calculated when the object or a substance is in a steady state (for example, a solid). This means that the substance is not changing between different states. This article discusses both heat capacity and specific heat capacity because the two are related.

The molecular structure of metals is very rigid. The space between molecules is smaller in metals and other solids than it is in liquids and gases. This gives molecules less freedom to move, and less energy (heat) is required to make them move vigorously and to raise the overall temperature of the material. Because of this their specific heat capacity is very low. This means that it is very easy to raise the temperature of metals.

Water, on the other hand, has a very high specific heat capacity. Therefore, compared to other materials, it takes a lot more energy to heat one unit of mass of water by one degree. Specific heat capacity for water is significantly higher than that of many other fluids because the hydrogen atoms in water molecules have very strong bonds.

Water is a major component of most living organisms and plants on Earth, and its specific heat capacity is a very important property for all living beings. Thanks to its high specific heat capacity, even on very hot days the heat is generally not high enough to raise the temperature of the internal fluids in animals and plants significantly.

Water forms a thermal regulation system in bodies of living organisms and plants, as well as a more global system that controls Earth’s temperature and climate. This is because a large portion of our planet is covered by water. Even if the heat generated by solar radiation is high, it takes a long time to raise the temperature of the oceans and other bodies of water, and the overall changes in temperature are very gradual. On the other hand, planets that do not have such extensive water coverage as does Earth, or even places on Earth with very little water, for example, deserts, have a much larger temperature fluctuation when the amount of solar heat changes. For example, the air temperature difference in the desert between daytime and nighttime is much more significant than the temperature fluctuation near or above the surface of an ocean.

Water’s high heat capacity means that it loses heat slowly, which makes it an excellent cooling agent. It is often used because water is generally cheap. In countries with cold climates, it is circulated in pipes in houses to provide heating. Water in a solution with ethylene glycol is also used in car engines for cooling. Ethylene glycol has a lower heat capacity, so it lowers the overall heat capacity of the solution and hence the effectiveness of the cooling system. However, at the same time, it ensures that the solution does not freeze in cold temperatures. Cooling liquid meant for cold climates uses more ethylene glycol — antifreeze is one of the formulations used in this situation.

The heat capacity of materials affects how fast they heat up when all other conditions are equal. Materials with high heat capacity require more energy than those with low heat capacity, therefore if an object with low heat capacity and an object with high heat capacity are heated with the same amount of energy under the same conditions, then the temperature of the object with lower heat capacity will increase faster. Materials with high heat capacity, on the other hand, take longer to heat up, but release this heat back into the environment a lot slower too.

We select materials based on heat capacity if we intend to use them to make everyday items such as pots and pans, tableware, and other objects that are subject to heat during their use. For example, it is generally better to use materials with low heat capacity such as metal for cooking utensils, pots or frying pans, to ensure that the heat passes to the food faster and to speed up the cooking process.

On the other hand, objects with high heat capacity take a long time to warm up and to cool down, therefore they are good insulators. We use such materials for cups and plates, especially if they are meant for hot foods. This ensures that the heat of the food is not lost quickly and that we do not burn ourselves. Some examples include ceramics and styrofoam.

Foods also have a different specific heat capacity and heat capacity. This often depends on the amount of water that makes up that food, but other factors are also at play. It is helpful to know the heat capacity of foods both when cooking and when eating them. Some foods act as insulators and, when placed on top of other foods, trap the heat underneath. If the foods under the insulators have a high heat capacity and are given enough energy to reach a high temperature, they already do not lose heat fast, and this property is even more enhanced by the “insulator” foods that cover them. They also do not lose water, because there is no place for it to evaporate.

Cheese is a good example of insulator food. When it is placed on top of another food, such as pizza, it melts and insulates the ingredients under it. There are usually ingredients under the cheese that have high water content, such as vegetables and sauce. Because of this, they have high heat capacity, so after they become hot, they do not lose this heat easily, and this property is further enhanced by the cheese insulator. This is why pizza straight out of the oven is very hot, and it does not cool down quickly. This property makes pizza delivery possible — if transported in a well-insulated bag, it arrives at the client’s door still hot.

Sauces are sometimes used in a similar manner as cheese. They are especially good insulators if they have a high-fat content, for example, cream sauces.

Inedible insulators are also sometimes used in cooking. For example, chefs in Central America, the Philippines, India, Thailand, Vietnam, and many other countries use banana leaves in place of edible insulators. Aluminum foil is often used in the same way as well. Not only does it prevent the water from evaporating and keeping the heat inside, but it also stops the protruding parts like chicken or turkey wings from overheating and burning as a result.

Foods high in fat or oil, such as cheese, have low heat capacity. They become hot with less heat than high heat capacity foods, and this often allows them to reach temperatures high enough for a browning reaction, known as the Maillard reaction. It is a chemical reaction between certain sugars and amino acids that changes the look and the flavor of food and is essential in many cooking methods such as baking and frying. We use oils for frying and deep-frying to increase the temperatures on the surface of different foods, to create conditions necessary for the Maillard reaction.

Sugar has an even lower heat capacity than oil. It becomes hot very quickly and can be a hazard during cooking, especially when making candy or caramel. When melting sugar, the chef must take necessary precautions to make sure that melted sugar is not spilled accidentally on the skin. If such a spill happens, it may cause a severe burn because sugar used for cooking can reach temperatures as high as 175° C (350° F). In some cases, the chef may need to check the temperature and consistency of the sugar, but it must be done with a thermometer, to avoid touching it with bare skin. Depending on what purpose the melted sugar is used for, a cold water drop method explained below may help determine sugar’s temperature and consistency.

When sugar or sugar syrups are cooked at different temperatures they have different properties. Heated sugar syrup could be liquid like the most liquid honey, solid, or anything in between. Recipes usually specify what temperature the sugar needs to reach to be ready to use, but they also often specify the name of the stage that it reaches, such as the soft-ball stage or the hard-ball stage. The stage name corresponds to the consistency of the sugar. To determine this consistency the chef places several drops of the melted sugar in icy water to cool it down instantly, and then examines these drops with bare hands for consistency. For example, if the sugar is not liquid but pliable enough to make a ball, it is in a soft-ball stage. If it is solid once cool and it is difficult but possible to change its shape with fingers, then it is in a hard-ball stage. This is the cold water drop method. Often chefs use both the thermometer readings and the cold water drop method to check if the sugar is cooked to the right consistency.

It is useful to know the heat capacity of foods to ensure that they are heated or chilled to the right temperature, to prevent spoilage or growth of parasites. For example, to reach a given temperature, foods that have higher heat capacity need to be cooked or chilled longer or with more intensity, compared to foods with low heat capacity. Cooking times are, therefore, determined based on the heat capacity of the ingredients, which, in turn, is dependent on the water content and on the amount of the water that is evaporating. The latter is because water evaporation requires a large amount of energy. Often a thermometer is also used to check the temperature to determine whether the food is cooked — this is common when cooking meats or fish.

The effectiveness of heating foods in a microwave oven depends, among other things, on the specific heat capacity of the products used. When the oven is in operation, the microwaves that it emits cause the molecules in substances such as water or fats to move more frequently. This heats up the food. The lower specific heat capacity of oils makes their molecules easier to excite, and because of this fatty foods heat to higher temperatures than does water. This may cause the foods to brown as a result of the Maillard reaction. Foods high in water content do not undergo this reaction because it requires temperatures, which are higher than those that are reached by foods with high heat capacity.

The ability of fats and oils to reach high temperatures in the microwave oven can be a hazard, especially if the oven users do not follow appropriate safety precautions. For example, when cooking foods high in oil content, it is better not to use plastics at all because they could be melted by the high temperatures that fatty foods reach. It is also good to remember when eating such foods that they are very hot.