Often in problems in physics, energy values for different processes are given in calories. However, in the international system of measurements (SI), the accepted unit for this physical quantity is the joule. In the article, we will consider in detail the issue of converting kilocalories to joules.
What does the value mean?
It is necessary to deal with the very concept of "calorie". And then proceed to consider the question of how to convert kilocalories to joules.
It was introduced into physics in 1824 by the French scientist Nicolas Clement. At the end of the 19th century and in the first half of the 20th century, the calorie was often used to quantify energy processes. It was used as a measure of energy in the Technical System of Units.
The value is called a small calorie. It represents the energy (heat) that needs to be transferred to 1 gram of water in order to heat it by 1 degree Celsius.
There is also a big calorie. Its value is equal to the energy required to heat 1 degree already 1 kilogram of water. Taking into account prefixes for units of measurement, a large calorie is recorded as 1 kcal=1000 cal.
What is 1 kilocalorie in joules?
This question will seem simple to many. Indeed, for this you need to take 1 kg of water, heat it by 1 oC and measure how much heat was transferred during this process. The problem is that the heat capacity of water depends on its temperature.
If you look at the tabular data, you can observe how, in the temperature range from 0 oC to 100 oC, the heat capacity H 2O changes from 4174 kJ/kg to 4220 kJ/kg. Moreover, it first decreases, reaching a minimum at 30-40 oC, and then again increases up to the boiling point.
The way out of this difficult situation was found. Scientists have tied an off-system unit of energy to a specific water temperature. The two most commonly used temperatures are 15 oC and 20 oC.
In the first case, we are talking about a standard calorie, it is 4, 1868 J. In the second case, it is about a thermochemical calorie, it is slightly less than the standard one, and is equal to 4, 184 J. These values differ from each other only by 0.07%.
When solving problems in physics, it is recommended to use the larger of the given values, that is, 1 cal=4.1868 J, since this value is standard, recognized in many developed countries of the world.
Accordingly, 1 kilocalorie in joules will be equal to 4186.8 J or 4.1868 kJ.
Where is this knowledge important?
As mentioned above, a calorie is notused in science. There it is recommended to use the joule to measure energy.
Nevertheless, in the production of food products, the energy value of their contents is applied to the labels in kilocalories. As a rule, these values are duplicated by the corresponding figures in kilojoules. However, many modern diets are based on the use of a calorie system.
Why is it important to know the energy value of the foods a person eats? Because the difference between the consumption of calories and their intake in the form of food determines whether the weight will increase or not.
Everyone who has faced this question in their life knows that fats contain 2.25 times more energy per unit of mass than proteins and carbohydrates. In addition, there is such a thing as "empty calories", which refers to the harmfulness of products (they supply energy to the body, but do not contain nutrients and vitamins). Alcoholic beverages are a prime example of foods high in empty calories.
Example of problem solving
Let's solve a simple problem of converting kilocalories to joules. Let's say a person bought 2 kg of meat in a store. He knows that this product contains 1250 kcal/kg. You need to find the corresponding value in joules.
Since the mass of meat is 2 kg, then its calorie content is 2 [kg]1250 [kcal/kg]=2500 kcal. Knowing that 1 kcal=4186.8 J, we will use the proportion. We get: 25004186, 8=10467000 J or 10, 467 MJ.
