Chapter 4 heat and temp psci

Flashcard maker : Kaiya Hebert
The fahrenheit thermometer scale is _____ than the celsius scale
no more accurate
on the celsius temperature scale, the numbers relate to the ____ and _____ of water
boiling and freezing
Measures of heat energy
The metric unit of measuring work, energy, or heat is the joule (J).
-The metric unit of heat is the calorie (cal).
A calorie is the amount of energy needed to increase the temperature of 1 gram of water 1 OC (from 14.5 OC to 15.5 OC.
-A kilocalorie (kcal) is the amount of energy needed to increase the temperature of 1 kg of water 1 OC. One food calorie is actually one kilocalorie of internal potential energy.

-Note: In the heating and air conditioning trade, the British Thermal Unit (BTU) is still used. One BTU = the energy needed to raise 1 pound water by 1 degree F.

Internal energy refers to the
total potential and kinetic energy of the molecules
external energy refers to
total potential and kinetic energy of an object that you can measure directly
heat is the
total internal energy of an object
* WHY? the specific heat of copper is 0.093 cal/gC degrees and the specific heat of aluminum is 0.22 cal/gC degrees. The same amount of energy applied to equal masses, say, 50.0g of copper and aluminum, will result in…
a higher temperature for copper
*WHY? The specific heat of water is 1.00 cal/gC degrees, and the specific heat of ice is 0.500 cal/gC degrees. The same amount of energy applied to equal masses, say, 50.0 g of water and ice, will result in (assume the ice does not melt)…
a greater temperature increase for the ice
convection is
the transfer of heat that takes place by the movement of groups of molecules with higher kinetic energy is
radiation is
the transfer of heat that takes place by energy moving through space is
conduction
the transfer of heat that takes place directly from molecule to molecule is
the evaporation of water cools the surroundings and the condensation of this vapor ____ the surroundings
warms
latent heat of fusion
the heat involved in the change of phase from solid ice to liquid water is called
the energy supplied to a system in the form of heat, minus the work done by the system, is equal to the change in internal energy. This statement describes the…
first law of thermodynamics
if you want to move heat from a region of cooler temperature to a region of warmer temperature, you must supply energy. This is described by the
second law of thermodynamics
more molecules are returning to the liquid state than leaving the liquid state. This process is called
condensation
the temperature of gas is proportional to the
average kinetic energy of the gas molecules
the temperature known as room temperature is nearest to
20 decrees celsius
using the kelvin scale, the freezing point of water is correctly written as
273 K
the specific heat of soil is 0.20 kcal/kgC degrees, and the specific heat of water is 1.00 kcal/kgC degrees. This means that if 1 kg if soil and 1 kg of water each receives 1kcal if energy, ideally the soil will be…
4 degrees celsius warmer than the water
styrofoam is a good insulating material because
it contains many tiny pockets of air
the transfer of heat takes place because of density difference in fluids is
convection
the latent heat is “hidden” because it
goes into or comes out of internal potential energy
as a solid undergoes a phase change to a liquid, it ___ while ___
absorbs heat
remaining at a constant temperature
a heat engine is designed to
convert heat into mechanical energy
the work that a heat engine is able to accomplish is ideally equivalent to the
difference between the heat supplied and the heat rejected
suppose ammonia is spilled in the back of a large room. If there were no air currents, how would the room temp influence how fast you would smell ammonia at the opposite side of the room?
warmer is faster
*which of the following contains the most heat?
anytime a temp difference occurs, you can expect
heat movement from any higher temperature region
the cheese on a hot pizza takes a long time to cool because it has a __
high specific heat
* WHY the specific heat of copper is roughly three times as great as the specific heat of gold. For equal masses of copper and gold: copper stores _____ at the same temperature.
3 times as much heat
cooking pans made from copper ( specific heat 0.093 kcal/kgC degrees) would need ____ to achieve a certain cooking temp?
less heat
conduction best takes place in a
solid
convection best takes place in a
fluid
radiation is the only method of heat transfer that can take place in a
vacuum
what form of heat transfer will warm your body without warming the air in a room?
radiation
when you add heat to a substance, its temp
might stay the same
the great cooling effect produced by water evaporating comes from its high
latent heat
at temperatures above freezing, the evaporation rate can equal the condensation rate at _____ temperature
any temperature
the phase change from ice to liquid water takes place at
constant temperature
* go to page…which of the following has the greatest value for liquid water?
latent heat of vaporization
energy tends to degrade, becoming of lower and lower quality, supports the ___ law of thermodynamics
second
the second law of thermodynamics tells us that the amount of disorder, called entropy, is always increasing. Does the growth of a plant or animal violate the second law?
no, the total entropy of the universe increases
the heat death of the universe in the future is when the universe is supposed to
freeze at a uniform low temperature
British thermal unit
one btu is the amount of energy (or heat) needed to increase the temp of one pound of water 1 degree Fahrenheit
calorie
the metric unit of heat; defined as the amount of energy (or heat) needed to increase the temp of 1 gram of water 1 degree celsius
celsius scale
uses the freezing point and boiling point of water at normal atmospheric pressure, but it has different arbitrarily assigned values.
The celsius scale identifies the freezing point of water as 0 degrees and the boiling point as 100 degrees celsius
entropy
a thermodynamic measure of disorder- (disorder means randomized, spread out, no patterns, arrangement..etc)
Whenever energy freely transforms from one form to another, the direction of transformation is toward a state of greater disorder, and therefore toward on of greater entropy

IOW- the greater the disorder, the higher the entropy

“the total entropy in the universe continually increases”
– The entropy of a system can decrease (more order- order means patterns and coherent arrangements), for example, when a heat pump cools and condenses the random, chaotically moving water vapor molecules into the more ordered state of liquid water
When the energy source for the production, transmission, and use of electrical energy is considered, however, the ‘total’ entropy increases.

external energy
the total potential and kinetic energy go an everyday sized object
Fahrenheit scale
90
first law of thermodynamics

p. 105 has all formulas

the energy supplied to a thermodynamic system in the form of heat, minus the work done by the system, is equal to the change in internal energy.

Heat engine example: as the engine cycles to the original state of internal energy (U2-U1=0), all the external work accomplished must be equal to all the heat absorbed in the cycle.
The heat supplied to the engine from a high temp (QH) is partly converted to work (W), and the rest is rejected in the lower temp exhaust (QL). The work accomplished is therefore the difference in the heat input and output (QH-QL) so the work accomplished represents the heat used: W- J(QH-Q1)
J (joules) is the mechanical equivalence of heat
you can increase the internal energy (produce heat) as long as you supply mechanical energy (do work). The first law of thermodynamics states that the conversion of work to heat is reversible, meaning heat can be changed to work

Thermodynamics
is concerned with internal energy (U), the total internal potential and kinetic energies of molecules making up a substance, such as the gases in the simple heat engine (a device that converts heat into mechanical energy).

The variables of temperature, gas, pressure, volume, heat. etc, characterize the total internal energy, which is called the ‘state’ of the system; any two systems that have the same values of variables that characterize internal energy as said to be in the same state

The state can be changed in two ways: 1- by heat flowing into (Qin) /out (Q out) of it, 2- by work (W out) being done on the system (W in).

heat
the measure of the internal energy that has been absorbed or transferred from one body to another
internal energy
the total kinetic and potential energy of the molecules of an object
kelvin scale
91
kilocalorie
the amount of energy (or heat) needed to increase the temp of 1 kilogram of water 1 degree celsius
kinetic molecular theory p86
latent heat of fusion P100 **
def- the heat involved in a solid-liquid phase change in melting or freezing.
consider the changes that occur when ice is subjected to a constant source of heat. (p.100 figure 4.18) When the temp reaches the melting point (0 degrees), it stops increasing as the ice begins to melt. More and more liquid water appears as the ice melts, but the temp remains at 0 degree celsius even though heat is still being added at a constant rate. It takes a certain amount of heat to melt all the ice. Finally, when all the ice is completely melted, the temp increases again at a constant rate between melting and boiling points.

Then at a constant temp the addition of heat produces another phase change, from liquid to gas. The quantity of heat involved in this phase changed is used in doing the work of breaking the molecule to molecule bonds in the solid, making a liquid with molecules that are now free to move about and rollover one another. Since the quantity of heat (Q) is absorbed without a temp change, it is called the latent heat of fusion (Lf)

In the case of latent heat of fusion, the work done in breaking the molecular bonds in the solid gave the molecules more___.
potential energy

This energy is “hidden” or latent since heat was absorbed but a temp increase did not take place. This same potential energy is given up when the molecules of the liquid return to the solid state.

a melting solid absorbs energy and a freezing liquid releases the same amount of energy, warming the surroundings.
Thus, you put ice in a cooler because the melting ice absorbs the latent heat of fusion from the beverage cans, cooling them.

for water, the latent heat of fusion is 80.0 cal/g. This means that every gram of ice that melts in your cooler absorbs 80.0 cal of heat. Every gram of water that freezes releases 80.0 cal. The total heat involved in a solid-liquid phase change depends on the mass of the substance involved.

latent heat of vaporization
def- “the heat involved in a liquid-gas phase change where there is evaporation and condensation” –It is the energy gained by the gas molecules as work is done in overcoming molecular forces.
This, escaping molecules absorb energy from the surroundings, and condensing gas/vapor releases this exact same amount of energy.

for water the latent heat of vaporization is 540.0 cal/g. This means that every gram of water vapor that condenses on your bathroom mirror releases 540.0 cal, which watts the bathroom. The total heating depend on how much water vapor condensed.

Evaporation p 102-103
If a molecule of water that has an exceptionally high energy is near the surface and is headed in the righ direction, it may overcome the attractive forces of the other water molecules and escape the liquid to become a gas. This process is called evaporation. It reduces a volume of liquid water as molecules leave the liquid state to become water vapor in the atmosphere.
Note: molecules that evaporate move about in all directions, and some will return, striking the liquid surface
condensation
The same forces that the molecules escaped from earlier capture the molecules, returning them to the liquid state. This process is called condensation. It is the opposite of evaporation– in evaporate, more molecules are leaving the liquid state than are returning. In condensation, more molecules are returning to the liquid state than are leaving.

When the condensation rate equals the evaporation rate, the air above the liquid is said to be ‘saturated’

Note: there is no net energy flow when the air is saturated, since the heat carried away by evaporate is returned by condensation. This is why you fan your face when you are hot. The moving ir from the fanning action pushes away water molecules from the air near your skin, preventing the adjacent air from becoming saturated, thus increasing the rate of evaporation.

molecule p 87
the smallest particle of a compound or gaseous element that can exist and still retain the characteristic properties of that substance.
phase change
when a solid, liquid, of gas changes from one phase to another= phase change
it absorbs or releases a quantity of heat that is not associated with temperature change.
Since the quantity of heat associated with a ohase change is not associated with a temp change, it is called ‘latent heat’

latent heat= “hidden” energy of phase hanges, which is energy (heat) that goes into or comes out of internal potential energy

3 kinds of major phase changes that can occur p.99***
1-solid-liquid
2-liquid- gas
3-solid-gas

–Solid -liquid phase change occurs when a solid melts to a liquid or a liquid freezes to a solid. Ice melting and water freezing to ice are examples of phase change and its two directions. They both occur at a temp called “the freezing point” or the “melting point” depending on the direction of the phase change. In either case, the freezing and melting points are the same temp

–liquid gas phase change also occurs in two diff directions. The temp at which a liquid boils and changes to a gas (or vapor) is called the “boiling point.” The temp at which gas or vapor changes back to liquid is called the “condensation point.”(boiling and condensation points are same temp)- other conditions liquids may turn to gas phase change is evaporation and condensation.

solid-gas on other card

Solid-gas phase change
solid-gas phase change takes…a phase change that takes a solid directly to a gas or vapor is called “sublimation”
mothballs and dry ice (solid CO2) are common examples of materials that undergo sublimation; frozen water or common ice also sublimates under certain conditions

ex: ice cubes in a freezer become smaller with time as a result of sublimation. The frost that forms in a freezer, on the other hand is an example of a solid-gas phase change that takes place in the other direction.
In this case, water vapor forms the frost without going through the liquid state, a solid gas phase change that takes place in an opposite direction to sublimation.

ex: consider the changes that occur when ice is subjected to a constant source of heat. (p.100 figure 4.18) When the temp reaches the melting point (0 degrees), it stops increasing as the ice begins to melt. More and more liquid water appears as the ice melts, but the temp remains at 0 degree celsius even though heat is still being added at a constant rate. It takes a certain amount of heat to melt all the ice. Finally, when all the ice is completely melted, the temp increases again at a constant rate between melting and boiling points.

second law of thermodynamics
heat flows from objects with a higher temp to objects with a cooler temp. IOW- if you want heat to flow from a colder region to a warmer one, you must ’cause’ it to do so by using energy (work)
ex: heat pump (moves heat in the opposite direction)
Never flows from cold to hot unless work is done on the system or energy is added from another source as in heat pumps and air conditioners
In the second law… energy can be viewed from two considerations of scale
1- the observable external energy
2- the internal energy of the molecules, or particles that make up an object
ex: a ball has kinetic energy after it is thrown through the air, and the entire system of particles making up the ball acts as a single massive particle as the ball moves.
In the second law…two kinds of motion make that the particles of an object can have:
1-a coherent motion- where the move together
2-an incoherent motion- chaotic motion of individual particles.

-Work on an object is associated with coherent motion, while heating an object is associated with its internal incoherent motion.

Some forms of energy, such as electrical and mechanical, have a greater amount of order since they involve particles moving together in a coherent motion. The term ‘quality of energy’ is used to identify___
the amount of coherent motion
high quality energy is

low quality energy is

high quality is energy with high order and coherence; can be easily converted to work

low quality is energy with less order and coherence; less able to do work

Degradation of energy
transformation of high quality energy to low quality energy.
energy becomes less and less available to do work. Eventually the upgraded mechanical energy will degrade to heat, and the increased heat will disperse through the processes of heat flow.
specific heat
the amount of heat needed to increase the temp of 1 gram of a substance 1 degree celsius
temperature
measure of the average kinetic energy of the molecules making up the substance
Four Ways to Increase the Rate of Evaporation of a Liquid Substance into the Space Above
-Increase the temperature of the liquid
Average molecular KE increases
More molecules have sufficient KE to escape
-Increase the surface area of the liquid exposed to the space above

-Decrease the number of molecules of substance in gaseous phase in the space above
Molecules in liquid phase are encouraged to repopulate space above
-Decrease the overall pressure of all gases in the space above
Pressure creates a force acting against molecules escaping liquid phase. Lower pressure lower force

Heat p92
the measure of internal energy that has been absorbed or transferred from one body to another.
The process of increasing internal energy is called heating; the process of decreasing internal energy is called cooling.

Get instant access to
all materials

Become a Member