# Physics Ch 4

Flashcard maker : Jonathan Walsh
British thermal unit (Btu)
One Btu is the amount of energy (or heat) needed to increase the temperature of 1 pound of water 1 degree Fahrenheit.
Calorie (cal)
Defined as the amount of energy (or heat) needed to increase the temperature of 1 gram of water 1 degree Celsius. 1 calorie = 4.184 joules.
Kilocalorie (kcal)
The amount of energy needed to increase the temperature of 1 kilogram of water 1 degree Celsius.
Kinetic Molecular Theory
Theory that all matter is made up of tiny, basic units of structure called atoms.
Element
smallest particle which retains the chemical properties of that element.
Phases
Solid, liquid, and gaseous
Solids
have both a definite volume and a definite shape
Liquids
have a definite volume but no definite shape
Gases
have no definite volume or no definite shape
Cohesion
defined as the attractive force between the same kinds of molecules
defined as the attractive force between unlike molecules
Molecule
Defined as the smallest particle of a compound or a gaseous element that can exist and still retain the characteristic properties of that subject.
Vapor
a substance in a gaseous state that normally exists in the liquid state at room temperature and pressure.
Plasma
refers to an “ionized state” of matter. When atoms of matter in the gaseous state have their outer electrons removed such that they become “charged particles”.
Fluids
refer to both liquids and gases, because they both can “flow”.
Temperature
A measure of the average kinetic energy of the molecules making up the substance.
Celsius scale
Invented by a Swedish astronomer. Water was used as the standard, with 0C being freezing temp and 100C as the boiling temp of water. This scale is also known as the Centigrade scale and is associated with the SI unit system.
Fahrenheit scale
Invented by a German physicist in about 1715. Water was used as the standard, with 32F set as the freezing temp and 212F as the boiling temp of water. Associated with the English system of units.
Kelvin scale
The zero point is thought to be the lowest limit of temperature. Absolute zero is the lowest temp possible, occurring when all random motion of molecules was historically projected to cease. Absolute zero is written as 0k. -270C = 0K.
Rankin scale
Absolute scale for the English system.
External energy
The total potential and kinetic energy of an everyday-sized object.
Internal energy
The total kinetic and potential energy of the molecules of an object. Represented by “U”.
Heat
A measure of the internal energy that has been absorbed or transferred from one body to another.
2 ways heating can occur:
1) from a temperature difference, with the energy moving from the region of higher temperature 2) from an object gaining energy by way of an energy-form conversion, which includes doing work on it.
Specific heat
Defined as the amount of heat needed to increase the temperature of 1 gram of a substance 1 degree Celsius.
Conduction
The transfer of energy from molecule to molecule.
Convection
The transfer of heat by a large-scale displacement of groups of molecules with relatively higher kinetic energy.
Involves the form of energy called radiant energy, energy that moves through space.
Phase change
When a solid, liquid, or gas changes from one phase to another. Always absorbs or releases a quantity of heat that is not associated with a temperature change.
Latent heat of fusion (Lf)
The heat involved in a solid-liquid phase change in melting or freezing. For water the latent heat of fusion is 80.0 cal/g.
Latent heat of vaporization (Lv)
The heat involved in a liquid-gas phase change where there is evaporation or condensation. For water, the latent heat of vaporization is 540.0 cal/g.
The first law of thermodynamics
states that 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.
The second law of thermodynamics
states that heat flows from objects with a higher temperature to objects with a cooler temperature.
Entropy
A thermodynamic measure of disorder ( no patterns, randomized, and spread out). The total entropy of the universe continually increases.
The Fahrenheit thermometer scale is
no more accurate than the Celsius scale.
On the Celsius temperature scale
the numbers relate to the boiling and freezing of water
Internal energy refers to
total potential energy and kinetic energy of the molecules.
External energy refers
total potential energy and kinetic energy of an object that you can measure directly.
Heat is the
total internal energy of an object.
The specific heat of copper is 0.093 cal/gC, and the specific heat of aluminum is 0.22 cal/gC. The same amount of energy applied to equal masses, say, 50.0 g of copper and aluminum, will result in
a higher temperature for copper.
The transfer of heat that takes place by the movement of groups of molecules with higher kinetic energy is
convection
The transfer of heat that takes place by energy moving through space is
The transfer of heat that takes place directly from molecule to molecule is
conduction
The evaporation of water cools the surroundings, and the condensation of this vapor
warms the surroundings
The heat involved in the change of phase from solid ice to liquid water is called
latent heat of fusion
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 are leaving the liquid state. This process is called
condensation
The temperature of a gas is proportional to the
average kinetic energy of the gas molecules
The temperature known as room temperature is nearest to
20C
Using the Kelvin temperature scale, the freezing point of water is correctly written as
273 K
The specific heat of soil is 0.20 kcal/kgC, and the specific heat of water is 1.00 kcal/kgC. This means that if 1 kg of soil and 1 kg of water each receives 1 kcal of energy, ideally
the soil will be 4C warmer than the water.
Styrofoam is a good insulating material because
it contains many tiny pockets of air
The transfer of heat that takes places because of density difference in fluids is
convection
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
absorbs heat while 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 temperature 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?
A barrel of water at 0C
Anytime a temperature 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
The specific heat of copper is roughly three times as great as the specific heat of gold. Which of the following is true for equal masses of copper and gold?
A piece of copper stores three times as much heat at the same temperature.
Cooking plans made from which of the following metals would need less heat to achieve a certain cooking temperature?
Copper
Conduction best takes place in a
solid
Convection best takes place in a (an)
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?
When you add heat to a substance, its temperature
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 only at
any temperature
The phase change from ice to liquid water takes place at
constant temperature
Which of the following has the greatest value for liquid water?
latent heat of vaporization
Which of the following supports the second law of thermodynamics?
Energy tends to degrade, becoming of lower and lower quality.
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
What is the specific heat of water?
1.0
4 ways to increase evaporation:
1) raise liquids temp
2) increase the surface area of the liquid
3) remove the vapor just above the liquid’s surface
4) by lowering the pressure of the liquid
3 facts of the second law of thermodynamics
1) all naturally-occurring processes go in the direction that increases entropy
2) the net effect of all processes raises the total entropy of the universe
3) no engine can be made which converts all absorbed heat into work
What is the average speed at room temp?
400 m/sec
The space above the liquid’s surface is said to be
saturated (100% humidity)
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 is the only method of heat transfer that can take place in a
vacuum
Anytime a temperature difference occurs, you can expect