Calorimetry – Heat moves the world and is also essential for our survival. Proof of this is fire, without it we cannot eat or keep warm.
Heat, in other forms, is indispensable to our daily lives. THE calorimetry studies these phenomena.
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THE calorimetry it is the study of phenomena that are related to thermal energy exchanges. This transit of thermal energy is called heat and happens due to the temperature between bodies.
Heat is the energy transferred from one body to another, the only difference being the temperature between the bodies. This transfer of energy in the form of heat occurs from the body with the highest temperature to the body with the lowest temperature.
When the bodies are thermally insulated on the outside, the transfer takes place until the bodies' equal temperatures are reached, that is, thermal equilibrium.
A body has internal energy and not heat itself. That's why it's only when energy is being transmitted that heat will exist.
Energy, which is in the form of heat, produces a change in body temperature called sensible heat. When the physical state of the body changes, this energy is called latent heat.
Thermal energy in transit has its magnitude called the amount of heat (Q). The unit of quantity of heat is the Joule (j) according to the International System (SI).
In practice, the unit called calorie (cal) is also used. Being:
1 cal = 4.1868 J
The specific heat (c) would be the constant of proportion of the fundamental equation of calorimetry. This value depends directly on the substance existing in the body to be studied.
The specific heat of iron is 0.00 cal/gº C. The specific heat of liquid water is 1 cal/gº C.
The thermal capacity is a quantity where the mass and substance of which the body is made is calculated.
C = m.c
Being that
C = thermal capacity (j/°C or cal/°C)
m = mass (kg or g)
c = specific heat (J/kgº C or lime/gº C)
1.5 kg of water were placed in a pan at room temperature (20ºC). When heated, the water temperature rises to 85°C. Taking into account that the specific heat is 1 cal/gº C.
The amount of heat received by the water to reach this temperature and the thermal capacity of that portion of water are calculated. To solve this case, we need to replace all values in the fundamental equation of calorimetry.
Attention to unity is very important. The mass of water is reported in kilograms. As the specific heat unit is in cal/gº C.
It is possible to calculate the amount of heat received or transferred to a body that has changed its physical state.
While this body is receiving this energy, changing phases, its temperature is constant. This latent heat is the following formula:
Q = m. L
Q = amount of heat (J or lime)
m = mass (kg or g)
L = latent heat (J/kg or cal/g)
How much heat is needed for a 600 kg block of ice at 0°C to be turned into water at that temperature? It is necessary to consider that the latent heat of melting ice is 80 cal/g.
For this calculation, replace the formula values, not forgetting to transform the units:
m = 600 kg = 600 000 g
L = 80 cal/gº C
Q = 600 000. 80 = 48 000 000 cal = 48 000 kcal
When two or more bodies exchange heat, this heat transfer will take place in such a way that the body with a higher temperature will transfer this heat energy to the body with a lower temperature.
In isolated thermal systems, these heat exchanges will take place until the thermal balance between them is established. The final temperature will be the same between the bodies. And when this stage is reached, the total energy is conserved.
It is the time when heat transfer from one body to another takes place.
Heat propagation takes place in three different ways:
The thermal conduction studied in calorimetry, happens when there is heat propagation through thermal agitation that occurs in atoms and molecules.
This agitation is passed on to the body as long as there is a difference in temperature between them. It is important to emphasize that for this transmission of thermal energy to occur, that is, heat, a material is needed to be the conductor. They are usually solids or fluids.
There are materials that make this conduction easier. Among them are metals. There are also thermal insulators, which conduct heat imperfectly. They would be wood, cork and Styrofoam.
An example of this conduction heat would be a fire pan with an aluminum spoon. The spoon heats up very quickly, it could even burn our hand.
That's why the spoon has wood or specific materials where we hold them, to avoid burns.
Thermal convection is the transfer of heat during the transport of heated material due to the difference in density. This occurs in liquid and gaseous bodies (gases).
When the substance is heated, the density of this body decreases. This change in body density creates a movement within the gaseous or liquid body.
The part that has been heated will rise and the denser part of the body will descend, thus creating a movement within the liquid or gas. This is called convection currents.
This accurately explains the heating of water in a pot. Through these convection currents, the hottest water rises and the coldest, which would be the densest, descends.
Thermal irradiation transfers heat through electromagnetic waves. This transmission of thermal energy does not need a material medium for bodies to receive this energy.
An example of this is the solar radiation on our planet, here the bodies are not in contact.
When a body is hit, some of the radiation is absorbed and this part is reflected. The amount of radiation absorbed will increase the kinetic energy of the body's molecules.
When bodies are dark, they absorb more radiation that is on them. While light bodies have a tendency to reflect this radiation.
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