In this article, we will answer the question: “What is a calorimeter?”. We define the general characteristic of this mechanism, its principle of operation and scope, functionality and measurement values. And also pay attention to the classification and description of some specific species.
Introduction
Answering the question of what a calorimeter is, in general terms it can be described as a device by which the amount of heat is measured, which is released or absorbed during physical, chemical or biological processes.
To introduce a new terminological unit “calorimeter” was proposed in 1780 by P. Laplace and A. Lavoisier. A similar device is also used in the nuclear branch of physics, which studies elementary particles, and it is called an ionization calorimeter. However, the function of this device is to measure the energy potential of particles.
Modern mechanism
Determination of heat capacity by a calorimeter of modern production allows us to fix the studied value with an accuracy of ten to one hundredth of a percent. The range in which this device can operate ranges from 0.1 to 3500 Kelvin. The type of calorimeter device is very diverse. It can be determined by the nature of the process being studied, as well as its duration. Another important parameter for determining the type of mechanism is the temperature range in which measurements are taken, as well as the amount of measured heat value.
Determination of the energy equivalent by a calorimeter can show the subject the amount of body that is released during the combustion of a fuel resource. This can be done thanks to the expression Q = C∆T, in which C is the indicator of the thermal (energy) equivalent. Set determination parameters by calibrating the instrument. Another quantity ∆T is a function of the known output signal of the calorimeter.
Type distribution
It is impossible to answer the question of what a calorimeter is without becoming familiar with its types.
One of the most common representatives of such devices is the integrator calorimeter. It is intended to determine the total amount of heat Q, which is released at the beginning of the reaction and its end.
Another widely known calorimeter is a device for measuring heat power, that is, the rate at which heat is released - L. And they can also be divided according to the design of the mechanism and the measuring methodology, approach. Liquid and massive calorimeters are also distinguished. There are also single and differential devices.
Heat measurement
What is a calorimeter in physics? The definition says that it is a device for measuring the amount of heat released. In this case, the heat released during the chemical reaction can be recognized only thanks to the liquid integrator calorimeter.
The design is presented in the form of a vessel filled with a liquid (usually water). It has a chamber for carrying out the experiment ("calorimetric bomb"), a stirrer, a thermometer and a device for heating.
Calorimetric System Measurements
The introduction of corrections into the natural course of heat generation of the system can be detected when any of its states changes. They, in turn, are determined by analyzing the amount of heat that is introduced into the device. The determination of the constant of the calorimeter takes place before the start of the measurement work and is compared with a predetermined and adjusted value. Devices are calibrated, which determines the coefficient. It must be multiplied with the temperature measured by the thermometer.
Side effects
In fact, calorimetric data directly show only the total number of heats that are investigated in the process. You can also find out about the presence of a side process (or processes) that could cause the phenomenon of mixing, evaporation of the liquid, as well as breaking the ampoule with substances, etc. Determining the constant of the calorimeter allows a person to access a comparison of the indicators of changes against the background of something. It is with its help that information is analyzed.
The heat of the secondary series of processes should be determined using experience or calculation, excluded from the research results. An example of a side effect is the inevitable heat transfer between the calorimeter and the surrounding space and matter.
Isothermal Observations
There is an isothermal type calorimeter integrator that allows you to introduce changes in the state of aggregation of bodies, which form the main part of the system. An example is the melting mass of ice in the ice chamber of a Bunsen calorimeter. You can find out the change in heat, which affects the state of aggregation, but does not cause a temperature change, if you calculate the mass of the substance and the amount of heat that would have to be spent for this.
To determine the specific heat of a calorimeter, you need to know that it is numerically equal to the amount of heat that is expended to heat a unit mass of matter. Its unit is J / kg▪K.
It is important to remember that the indicator of specific heat is an ambiguous characteristic. There is a relationship between the conditions of heat transfer and the value of the work that accompanies this process.
Massive type
Massive integrators are used to determine the enthalpy of a substance at temperatures up to 2500 degrees Celsius. The mass of a calorimeter of this type can vary depending on the weight of the measured substance, since the structure is composed of metals. In fact, this is a block with a certain number of recesses for vessels. They carry out reactions intended for a heating device and / or thermometer. The product of the heat measured by the calorimeter and the difference in temperature rises in the block shows us the enthalpy of substances (a).
Flow
You can determine the heat capacity of a gas or liquid using a flowing labyrinth calorimeter. It fixes the temperature difference, which enters and leaves the stationary flows of the test substance. It also determines the power of such a flow and the strength of the heat that is released by the electric heater in joules.
Power meter
When answering the question of what a calorimeter is, it will be important to mention the purpose of this device for determining power. Such an apparatus, unlike an integrator, must be endowed with a significant ability for heat transfer. This is necessary so that he can remove the amount of heat that is introduced into it. It follows that the state of the calorimeter is in instantaneous measurement.
The thermal value of the power of the process is found by using calorimeters with a shell. The invention was made by a physicist from France, E. Calvet. Initially, the mechanism was presented in the form of a metal block equipped with channels. They laid out special cylindrical cells designed for the process under study. The metal used in the construction of the chamber is a shell. Its temperature should be kept at a constant mark with an accuracy of five to six Kelvin.
The difference between the temperature of the cell and the unit is measured using a thermal battery with up to a thousand adhesions. The indicators of its EMF and heat transfer of the cell are proportional to the small difference in temperature that has arisen between such components as the unit and the cell. In this case, heat must be released or absorbed in the cell itself. Very often in such blocks have a pair of cells that will work differentially.
Title and classification
Common names for calorimeters are:
- for chemical reactions;
- bombing;
- isothermal type;
- low temperature type;
- ice type.
All of them have data on historical origin. They usually owe their name to the area in which they will be used. However, these names do not refer to a comparative or full description.
A general view of the classification of calorimeters is constructed using, as a basis, a consideration of one of the three main quantities, individually or together. It is the approach to the analysis of indicators that determines the method of measuring temperature, which has:
- calorimetric system Tc;
- shell To;
- the amount of released heat L per unit time (thermal power).
Calorimeters with a constant value of Tc and T0 are of the isothermal type, and devices in which Tc = T0 are called adiabatic. If the device operates in conditions with a constant difference between temperatures, then it is called a calorimeter with a constant flow of heat transfer. The isoperibolic mechanism has a constant To, and Tc is the thermal function of power L.
Final results
There are a number of factors that can affect the final measurement result. One of them is the availability of changes affecting their final result. It is due to the reliability of the automatic set of temperature regulators of an isothermal or adiabatic shell. In the last of them, the temperature value is determined by its proximity to the changing conditions of the entire calorimetric system. This design has the ease of a metal screen and is equipped with a heating device, which reduces the flow and value of heat transfer to a certain level at which the temperature of the calorimeter will change only by decimal parts of a degree per minute. This can reduce the heat transfer during the calorimetric experiment to extremely low values that can be neglected.
The devices considered in the article play a huge role in human life and are one of the very significant achievements of science. The main function of the calorimeter is to study the data of temperature changes and determine the presence of defects in the process of heat transfer. There are various ways to classify these devices, associated with specific parameters that differ sharply from each other. The material for the manufacture can be a variety of metals, for example, there are copper calorimeters, lead, steel and others. In addition to pure substances, alloys can also be used.