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means of recognizing the interaction called heat (and particularly provides a means of
distinguishing this interaction from the one called work). In addition, we must have
some method of measuring heat.
Heat can be measured by the use of standard systems which can be made to change
from one readily recognizable state to another by means of the transfer of heat under
specified conditions. The magnitude of the heat transferred is then given by the number
of such standard systems which can be made to undergo the specified state change as a
result of the interaction. For example, suppose we wish to know how much heat is
transferred from a block of steel which cools from the temperature of boiling water at
one atmosphere (100°C) to the temperature of freezing water at one atmosphere (0°C).
The standard systems we use might be 1kg blocks of ice at 0°C. The steel block can be
cooled by being isolated with one such block of ice after another so that each block of
ice is melted but the temperature of the resulting liquid is not changed. The number of
such standard systems (blocks of ice) so used is a measure of the amount of heat
removed from the steel block. Of course, many different kinds of standard systems other
than blocks of ice could be used. The important conclusion is that it is possible to
describe certain operations by means of which heat can be measured; hence, heat can be
defined operationally.
The widely adopted sign convention for heat is that heat added to a system is
expressed by positive numbers and heat taken from a system is expressed by negative
numbers.
Heat, like work, is an interaction between systems. It is not a characteristic which
can be observed while a system is in a particular state. It is not a property of a system.
The amount of heat transferred to or from a system during a process cannot be
determined from the end states alone. Instead, the amount of heat transferred depends
on how the system was changed from one state to another. Heat, like work, is a path
function.
A full understanding of the differences between the two interactions, heat and work,
depends on the second law of thermodynamics. Nevertheless, it is well to review at this
point the essential difference between them which is established by their definitions:
Heat is an interaction caused by a temperature difference between a system and its
surroundings; work is done by a system if the sole effect of the system on its
surroundings could be reduced to the lifting of a weight.
A process in which there is no heat transfer is called an adiabatic pro which exchanges
no heat with its surroundings is called an adiabatic system.

1.6.5 Calculation of Heat Quantity
Quantity of the heat can calculate two way. One of them is connected with
conception of heat capacity or specific heat.
When we heat a body, its temperature rises, if it is not changing its state (i.e.
melting or boiling ). The quantity of heat, say Q, absorbed by the body depends upon
the rise of temperature, say T degrees. The greater the rise of temperature, the greater
the quantity of heat absorbed. Thus we have the relation :

Q =f(T) (1.30)

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