Download HEAT- Chapter 9

HEAT- Chapter 9
Temperature and Thermal Equilibrium
 The temperature of an object is proportional to the average
kinetic energy of particles in a substance
 The energy associated with atomic motion is internal energy(U).
 When energy is added to a substance, its average kinetic energy,
and thus its temperature increases
Thermal equilibrium
 Thermal equilibrium is reached when the thermal energy
of 2 substances is the same.
Thermal energy moves from hot to cold.
If a can of soda is placed in the freezer, the thermal
energy of the soda will transfer away from the can to
the outside air in the freezer. This will continue until the
can and its contents reach thermal equilibrium.
 Increasing the temperature of a gas at constant
pressure causes the volume of the gas to increase.
 Thermal expansion is the tendency of a substance, when
heated, to increase in volume.
 In general, the volume of a liquid will decrease as
temperature decreases; the exception is water
 Solids tend to have the smallest coefficient of volume
 Coefficient of Volume Expansion- a number assigned to
different material to show the thermal expansion
characteristic of the material
Gases have highest coefficient; solids the lowest
Measuring Temperature
 In a thermometer, the change in length of the liquid in
the thermometer is proportional to the temperature
change
 3 scales used to measure temperature:
Fahrenheit- used in United States
Celsius- used by other countries and scientific
community
Kelvin-a scale used by scientists that measures
absolute zero.
 Fahrenheit Scale:
 Freezing point of water: 32°
 Boiling point of water: 212 °
Celsius Scale
Freezing point of water: 0 °
Boiling point of water: 100 °
Kelvin Scale: 0 = absolute zero
Freezing point of water: 273K
Boiling point of water: 373K
 Heat – thermal energy that is transferred.
 Unit- Joules (J)
 Heat’s symbol- Q
Thermal Conduction: how heat is
transferred
Conduction- heat
travels through
touching atoms
(solids)
Convection- heat
transfer in fluids
Radiation-heat transfer
over a distance; can
take place through
the vacuum of space
Conservation of Energy- total energy is
conserved
ΔPE + ΔKE + ΔU= 0
The change in potential energy + the change in KE +
the change in internal energy = 0
Changes in Temperature & Phase
Specific Heat Capacity-the energy required to change
the temperature of 1kg of a substance by 1° C
Every substance has a unique Specific Heat capacity.
Tells how much the temperature of a given mass of a
substance will increase or decrease, depending on the
how much energy is added or removed as heat
C𝑝= Q/mΔT:
 Specific Heat Capacity=energy transferred as heat/mass x
change in temperature
Specific Heat Capacities Table
Calorimeters- used to determine the specific heat of
substances
𝑪𝒑𝒘 𝑴𝒘 ∆𝑻𝒘 = −𝑪𝒑𝒙 𝑴𝒙 ∆𝑻𝒙
w stands for water;
Specific heat x Mass(kg) x change in Time=
Released heat x Mass(kg) x change in time
Phase Changes & Temperature
Temperature increases
until a phase change.
During the phase
change, temperature
does not increase or
decrease.
After all of the
substance has changed
phase, temperature will
increase (or decrease)
until the next phase
change.
Latent Heat-the heat required to convert a
solid into a liquid or vapor, or a liquid into a
vapor, without change of temperature.