Relationship between Heat, Temperature, and Thermal
Energy
It is important to note that thermal processes relate
the ideas of heat, temperature, and thermal energy together
along with other constants and variables; however, it is
crucial to understand that these three concepts are distinct
in what they represent and how they interact with the system
and environment in which they take place.
- Heat is denoted as the energy that is transferred
between the system and the environment as the two coexist
and interact. Heat is neither a state variable that is privy
and constant to the entire system nor is it a singular,
particular form of energy. Hence, one cannot assert or
catalog how heat changes within a reaction and interaction
between the system and environment as Q = 0 when there is no
interaction between the two bodies. Thus, heat affects the
thermal energy of the system by altering it and quantifying
the movement of energy in and out, but it is not synonymous
with thermal energy.
- Temperature quantifies the "hotness" or "coldness"
of a system, both a qualitative and quantitative property as
temperature exists as a state variable that is constant for
the whole system throughout the interaction. It relates to
the thermal energy present in the system by association with
the molecules and atoms inherently contained in the material
or fluid. Thus, a change in temperature is required for a
thermal reaction to take place in which heat moves into and
out of the system into the surrounding environment. By this
token, it is paramount that the assumption of a change in
temperature is equivalent to the addition of heat be
avoided, as the temperature of a system can also be changed
by performing work on the system or even transforming
mechanical energy to thermal energy by friction.
- Thermal Energy exists as the energy of a system
through motion of the inherent atoms and molecules that make
up the material or fluid. In this respect, thermal energy is
a state variable and thus can be cataloged and quantified as
it changes during a process. As such, the thermal energy of
a system continues to exist even when it is isolated from
the environment and no longer interacting thermally with its
surroundings. Hence, thermal energy can be changed by the
addition of heat to a system through interaction with the
environment and is also adjustable by performing work on the
system or requiring the system to perform work itself as
seen in engine processes. This relationship between change
in thermal energy as associated with work and heat is the
First Law of Thermodynamics and maintains the concept of
conservation of energy.
Thus, the three variables of heat, temperature, and thermal
energy interact and affect one another at both the macroscopic
and microscopic levels and are characteristics which one should
be aware of when a change in thermal energy occurs. As explained
above, both heat and work can be responsible for adjusting the
thermal energy and temperature of a system. This association
denotes changes in thermal energy as also being subject to
mechanical processes performed by both the system and the
environment, an important distinction in relating the overall
change in energy of a body as being quantifiable as the sums of
change in both mechanical and thermal energy to maintain
conservation of energy.