Energy in Thermal Process Flashcards
When two objects of different temperatures are
placed in thermal contact, the temperature of the
warmer decreases and the temperature of the cooler
increases
Energy Transfer
The energy exchange ceases when the objects reach
____
Thermal Equilibrium
is the energy associated with the
atoms and molecules of the system
Internal Energy
the transfer of energy between a system
and its environment because of a temperature
difference between them
– The symbol Q is used to represent the
amount of energy transferred by ____ between a system and its environment
Heat
Units of Heat
o ____ – An historical unit, before the connection
between thermodynamics and mechanics
was recognized
o A ____ is the amount of energy necessary to
raise the temperature of 1 g of water from 14.5°
C to 15.5° C .
Calorie
is the amount of energy necessary to
raise the temperature of 1 lb of water from
63° F to 64° F
This is called the Mechanical Equivalent of
Heat
BTU British Thermal Unit
____
o 1818 – 1889
o British physicist
o Conservation of Energy
o Relationship between heat
and other forms of energy
transfer
James Prescott Juole
o Used in one technique for determining the
specific heat of a substance
o A _____ is a vessel that is a good insulator
which allows a thermal equilibrium to be
achieved between substances without any
energy loss to the environment
Calorimeter
occurs when the physical
characteristics of the substance change from one
form to another
Phase Change
Some substances will go directly from solid to
gaseous phase
❖ Without passing through the liquid phase
Sublimation
o Start with one gram of ice at –30.0° C
o During A, the temperature of the ice
changes from –30.0° C to 0o C
o Use Q = m c ΔT
o Will add 62.7 J of energy
Warming Ice
o Once at 0° C, the phase change
(___) starts
o The temperature stays the same although energy
is still being added
o Use Q = m Lf
o Needs 333 J of energy
Melting Ice
o Between 0° C and 100° C, the material is liquid
and no phase changes take place
o Energy added increases the temperature
o Use Q = m c ΔT
o 419 J of energy are added
Warming Water
o At 100° C, a phase change occurs (____)
o Temperature does not change
o Use Q = m Lv
o 2 260 J of energy are needed
Boiling water
o After all the water is converted to steam, the
steam will heat up
o No phase change occurs
o The added energy goes to increasing the
temperature
o Use Q = m c ΔT
o To raise the temperature of the steam to 120°,
40.2 J of energy are needed
Heating Steam
Energy transferred by the movement of a
substance
❖ When the movement results from
differences in density, it is called (2 ___)
❖ When the movement is forced by a fan or a
pump, it is called (3 __)
Convection
- Natural Convection
- Forced Convection
o The transfer can be viewed on an atomic scale
❖ It is an exchange of energy between
microscopic particles by collisions
❖ Less energetic particles gain energy during
collisions with more energetic particles
Conduction
o ____ does not require physical contact
o All objects radiate energy continuously in the
form of electromagnetic waves due to thermal
vibrations of the molecules
o Rate of radiation is given by Stefan’s Law
Radiation
The power is the rate of energy transfer,
in Watts
Stefan-Boltzmann
constant
❖ The rate at which the object at temperature
T with surroundings at To radiates is
Energy Absorption and Emission by Radiation
The image of the pattern formed by
varying radiation levels is called a
thermogram
Thermography
Radiation thermometer measures the
intensity of the infrared radiation from
the eardrum
Body Temperature
