calorimetry ( calorimeter)
Calorimetry is the measurement of the quantity of heat lost or absorbed. There are many methods, which can be classified into two namely; Thermometric calorimetry and Latent heat calorimetry.
In Thermometric calorimetry a change in temperature is recorded as in:
– Method of mixtures: in which the heat to be measured is transferred to a known mass of water.
-Method of cooling: which depends on the fact that the rate of loss of heat from a hot body under constant conditions follows a regular law.
-Electrical method: in which the quantity of heat energy concerned is measured in electrical units.
The calorimeter is a metal Container inside which heat exchanges occurs during experiments involving heat flow.
It is made of good conductors, usually copper and Aluminum, So that it can quickly reach the temperature of its contents. It is also designed to minimize heat exchange between its contents and the surrounding. It can as well be seen as an apparatus used in experiments that involves exchange of heat between two bodies at different temperatures. The most common method employed in calorimeter experiments is known as the method of mixtures.
In a calorimetry experiment the quantity of heat lost by a hot substance must be equal to the quantity of heat gained by the cold substance. Loss in calorimeter are often through conduction, convention, evaporation and radiation. To reduce these losses, the calorimeter is lagged by providing the calorimeter with a lid containing a hole, to accommodate the thermometer and a stirrer.
Heat loss by radiation is reduced by polishing the outside of the calorimeter. The method of mixtures is used in the determination of the specific heat capacity of solids.
Heat lost by the material = Heat gained by water + calorimeter.
Final heat of material = final heat of water
Precautions to take while performing the experiment
During the heating of the specimen, it is important to ensure that the specimen reaches the temperature recorded by the thermometer in contact with the specimen. The specimen must be kept dry.
When transferring the specimen to the calorimeter, it should be done as quickly as possible and with uttermost care to avoid splashing water out of the calorimeter.
Latent heat
Suppose heat is continuously supplied to a block of ice which is solid at -8 degrees centigrade. There is a temperature change accompanying the heat supply. It will be observed that there is an increase in temperature of the ice until 0 degrees centigrade.
At this point, the ice starts to melt and as long as the ice continues melting, no temperature change will be observed. After the ice has melted completely, the temperature will begin to increase, this will continue until 100 degrees centigrade when the water starts boiling and changes to vapor. The temperature remains constant all through.
During the change of state, the heat supplied appears to be hidden. This heat is called hidden heat or latent heat because it does not make the substance any warmer. Latent heat is the heat supplied or removed which cause a change of state without a change in temperature. It depends on the mass and nature of the substance.
Latent heat of fusion is the quantity of heat required to convert a substance from its solid state to its liquid state without a change in temperature. The System of international units of specific latent heat of fusion (L) of a substance is joule per kilogram. To calculate heat involved, specific latent heat of fusion and mass are related by H= ML
Where H= heat involved
M= mass
L= latent heat of fusion
Method of mixtures is also used in the determination of the specific latent heat of fusion.
Good Calorimetry 1( calorimeter)
