Exam 3- Physics

Carnot cycle

- a cyclical process that uses only reversible processes, the adiabatic and isothermal processes - most efficient engine cycle

nonspontaneous process

- a process that only occurs as long as energy is continually added to the system - spontaneity depends on dispersion of energy that occurs during a process - energy spontaneously disperses if it is not hindered from doing so

spontaneous process

- a process that, once started, occurs without outside intervention

2nd law of thermodynamics

- amount of disorder in an isolated system always increases or stays the same (if the system is in equilibrium) - heat transfer occurs spontaneously from a body with higher temperature to the one with lower temperature - never spontaneous in the reverse direction - heat that transfers from a reservoir can not completely transform into work

heat transfer

- amount of energy transferred per unit time - radiation - conduction - convection

heat engine

- any device that operates in a closed cycle and takes heat from a hot reservoir, does useful work, and gives heat to a cold reservoir - can continue to do useful work for as long as it is attached to the reservoirs

3rd law

- at absolute zero temperature the system is perfectly ordered

energy

- capacity to do work - work done on the system increases energy in the system - work done by the system decreases energy of the system

work

- done to achieve motion against an opposing force - energy that stimulates orderly motion in the surroundings - raising weight against pull of gravity - expansion of gas that pushes a piston - chemical reaction in the cell

molecular speed

- energy is dissipated in collision, but total kinetic energy is conserved - distribution of molecular speeds

heat

- energy of the system that changes as a result of temperature difference -energy transferred to the surroundings stimulates random (thermal) motion of particles in the surroundings - depends on the boundary between system and surrounding: - diathermic: heat transfer is permitted - adiabatic: there is no heat transfer

Q

- heat --> energy transferred because of temperature difference - characterized by random molecular motion - highly dependent on path - Q entering a system is positive

specific heat

- heat changes an objects temperature - specific heat (constant c) indicates how easy it is to change an object's temperature - units: J/kg*K

heat and transfer

- heat is the transfer of energy from one place to another due to temperature difference - energy flow between objects due to temperature differences - energy flows from higher temp to lower temp until thermal equilibrium is reached

entropy

- how dispersed the energy in a system is at a specific temperature - energy distributed affected by molecular motion, volume - entropy of an isolated system increases in the course of a spontaneous change

0th Law of Thermodynamics

- if system A and B are in thermal equilibrium with system C, then A and B are in thermal equilibrium with one another

thermal expansion

- in general things expand when they are warmed and contract when they are cooled

entropy increases with:

- increasing temperature - increasing volume - increasing number of independent particles - as temperature increases, the amount of motion increases

U

- internal heat --> the sum of the kinetic and potential energies of a system's atoms and molecules - can be divided into many subcategories such as thermal and chemical energy - depends only on the state of a system, not on how the energy entered the system - change in internal energy is path independent

1st law

- interplay of internal energy of a system, the work system does on the surroundings and the heat that flows in or out of the system - used to analyze the change of the system during thermodynamic process

types of thermodynamic processes

- isobaric - isothermal - adiabatic - isochoric

adiabatic

- no heat flow into our out of the system

ideal gas particles

- occupy negligibly small volume - are in constant and random motion - do not interact

system

- part of the world of interest - classified based on the flow of energy and matter with surroundings

isobaric

- pressure held constant - W= p(Vf-Vi)

surroundings

- region outside the system where measurements are done

2nd law

- some thermodynamic processes are impossible, there is a limit to the efficiency of heat engines

isothermal

- temperature held constant

1st law of thermodynamics

- the change in internal energy of a system equals the net heat transferred into the system minus the net work done by the system

kinetic theory of gas

- the gas consists of molecules of mass (m) in constant random motion - the size of the molecules is negligible - the gas molecules do not interact - the molecules are involved in elastic collisions

average kinetic energy

- the internal energy of a perfect gas is independent of the volume it occupies

absolute zero (T)

- the lowest temperature theoretically possible in nature - the state where particles are perfectly still

temperature

- the measure of the average kinetic energy of molecules in a substance

thermodynamics

- the study of heat transfer and its relationship to doing work

reversible process

- the system and environment can be restored to exactly the same initial states that they were in before the process occurred - system is at equilibrium at any given moment of the process

irreversible process

- the system and its environment cannot be restored to their original states at the same time - the system is not at equilibrium at any given moment of this process

0th law

- the temperature is experimental parameter that can be transferred through multiple bodies

heat

- the transfer of energy from one place to another due to temperature difference

internal energy

- total energy of the system (U) - total kinetic energy and potential energy of all constitutes of the system - not a kinetic energy of a system as a whole - state function: depends only on a current state of a system, not on the path that system takes to get to that state

degrees of freedom

- translational - vibrational - rotational

thermal equilibrium

- two objects that share the same temperature

conduction

- uses collisions of molecules to transfer energy (little bubbles) - particles colliding with other particles and transferring their kinetic energy

radiation

- uses electromagnetic radiation to transfer energy - all objects with a temperature radiate energy

convection

- uses motion of molecules to transfer energy (rolling boil) - motion of molecules are very good at transferring energy - ex: heating or cooling a house

isochoric

- volume held constant

heat flow

- when heat flows into an object +Q - when heat flows out of an object -Q - measured in J

W

- work --> energy transferred by a force moving a distance - an organized, orderly process - path dependent - W done on a system (either against an external force or to increase the volume of the system) is positive

refrigerator

- works like a heat engine in reverse

At a particular point on a PV diagram, the magnitude of the slope of a curve that represents an adiabatic process is a) zero b) greater than that of an isotherm through the same point. c) infinite d) less than that of an isotherm through the same point. e) the same as that of an isotherm through the same point.

b) greater than that of an isotherm through the same point.

If you run a refrigerator in a closed room with the door to the refrigerator closed, the temperature of the room a) Any of these can happen depending on the relative sizes of the room and the refrigerator. b) increases c) Any of these can happen depending on how efficient the refrigerator is. d) decreases. e) remains the same.

b) increases

A refrigerator extracts heat Q from a cold reservoir. The heat exhausted to a hot reservoir a) is Q b) must be greater than Q. c) could be greater than Q for some refrigerators. d) is zero. e) must be less than Q.

b) must be greater than Q.

The first law of thermodynamics has as its basis the same fundamental principle as a) the continuity principle b) the conservation of energy c) Newton's law of universal gravitation d) the conservation of linear momentum

b) the conservation of energy

Earth receives about 1.7 × 1017 J of energy from the Sun each second through a process called a) Conduction b) Convection c) Radiation d) Sublimation

c) Radiation

The total mechanical energy of any system is a) Always the work done by gravity b) The difference between the kinetic and potential energy at any point c) The sum of the kinetic and potential energy at any point d) The sum of the translational and rotational kinetic energies at any point

c) The sum of the kinetic and potential energy at any point

Which of the following statements about absolute zero temperature is true? a) Absolute zero is defined at 273.15°C. b) At absolute zero all translational motion of the particles ceases. c) All of the answers are correct. d) At absolute zero all particles are at rest, except for quantum motion. e) At absolute zero all rotational motion of the particles ceases.

c) all of the answers are correct

The specific heat of a gas is a) independent of constraints imposed on it while heating. b) a negligible quantity. c) greater at constant pressure than at constant volume. d) the same for all gases. e) directly proportional to the absolute temperature.

c) greater at constant pressure than at constant volume.

The Carnot cycle consists of a) isothermal absorption of heat from a hot reservoir. b) isothermal exhaustion of heat to a cold reservoir. c) adiabatic compression to the initial state of the system d) All of the answers are correct. e) adiabatic expansion to a lower temperature.

d) All of the answers are correct.

If the pressure and volume of an ideal gas are both reduced to half their original value, the absolute temperature of the gas is a) Unchanged b) Doubled c) Increased by factor 4 d) Decreased by factor 4

d) Decreased by factor 4

When a substance changes phase, from solid to liquid or liquid to vapor and vice versa, there is no change in temperature, even though heat is being added or removed. Why is there no change in temperature? a) None of the answers are correct b) During a phase change, the temperature measured is the last temperature of the measuring device. c) During a phase change, temperature is not well defined since there are two phases involved. d) During a phase change, energy is used to break/establish the intermolecular bonds rather than stored as kinetic energy of the molecules. e) During a phase change, energy is needed to overcome the gravitational pull.

d) During a phase change, energy is used to break/establish the intermolecular bonds rather than stored as kinetic energy of the molecules.

If the absolute temperature of a gas is doubled, what is the change in the rms speed of its molecules? a) No change b) Increases by a factor of 2 c) Decreases by a factor of 2 d) Increases by a factor √𝟐

d) Increases by a factor √𝟐

The specific heat of a substance is a measure of a) none of the answers are correct. b) energy needed to liquefy/solidify the substance. c) energy needed to vaporize/liquefy the substance. d) energy needed to increase the kinetic energies of particles in the substance by one K e) total energy in the substance for a given temperature change

d) energy needed to increase the kinetic energies of particles in the substance by one K

A heat engine absorbs heat Q from a hot reservoir. The amount of work done by the engine a) is zero b) must be greater than Q. c) could be greater than Q depending on the type of engine d) must be less than Q. e) is Q

d) must be less than Q.

The amount of linear expansion of a rod does NOT depend on a) the change in the absolute temperature of the rod. b) the original length of the rod. c) the material from which the rod is made. d) the specific heat of the rod. e) the coefficient of linear expansion.

d) the specific heat of the rod.

if it is known that two bodies are in thermal equilibrium, one can conclude that a) there must be a net heat flow between them b) they must be in thermal equilibrium with a third body c) the bodies must be at different temperatures d) they must be at the same temperature e) none of the choices are correct

d) they must be at the same temperature

Of the four steps in the Carnot cycle a) two are isothermal and two are isobaric. b) two are adiabatic and two are isobaric. c) two are isovolumic and two are isothermal. d) two are adiabatic and two are isothermal.

d) two are adiabatic and two are isothermal.

Boltzmann's constant, k, has a value of 1.381 × 10-23 J/K. What is the significance of the constant? a) It defines a characteristic energy at the microscopic level, given the temperature in kelvins. b) It allows the pressure of the gas to be calculated, given the volume and temperature. c) It measures the average kinetic energy of a molecule at a given temperature for each degree of freedom. d) (a) and (b) e) (a) and (c)

e) (a) and (c)

There is no heat transfer into or out of a system during a(n) _____ process. Select one: a) isobaric b) There is always heat transfer during thermodynamic processes. c) isothermal d) isochoric e) adiabatic

e) adiabatic

If the absolute temperature of a gas is doubled, what is the change in the average kinetic energy of its molecules? a) decreases by a factor of √2 b) no change c) increases by a factor of √2 d) decreases by a factor of 2 e) increases by a factor of 2

e) increases by a factor of 2

You can double both the pressure and the volume of an ideal gas if you change the temperature of the gas by a) doing none of these. b) reducing it to one-half of its original value. c) reducing it to one-quarter of its original value. d) doubling it. e) quadrupling it.

e) quadrupling it.

The main process by which heat is transferred to your home when it is heated by solar energy is a) insulation b) conduction c) convection d) latent heat transfer e) radiation

e) radiation

The first law of thermodynamics has as its basis the same fundamental principle as a) the conservation of linear momentum. b) Newton's law of universal gravitation. c) the continuity principle. d) static equilibrium. e) the conservation of energy.

e) the conservation of energy.

The maximum possible efficiency of a heat engine is determined by a) its design b) the amount of heat that flows c) the maximum and minimum pressure d) the compression ratio e) the maximum and minimum temperature

e) the maximum and minimum temperature

In a system composed of gas contained in a cylinder fitted with a piston, an adiabatic expansion causes the temperature of the gas to drop because a) work is done on the system as the gas expands. b) heat is absorbed by the piston when it does work. c) heat is given up by the system when the piston moves. d) the pressure of the gas remains constant. e) work done by the system is entirely at the expense of its internal energy.

e) work done by the system is entirely at the expense of its internal energy.

When a substance changes phase, from solid to liquid or liquid to vapor and vice versa, there is no change in temperature, even though heat is being added or removed. Why is there no change in temperature? a) During a phase change, energy is used to break/establish the intermolecular bonds rather than stored as kinetic energy of the molecules. b) During a phase change, temperature is not well defined since there are two phases involved c) During a phase change, energy is needed to overcome the gravitational pull. d) During a phase change, the temperature measured is the last temperature of the measuring device.

a) During a phase change, energy is used to break/establish the intermolecular bonds rather than stored as kinetic energy of the molecules.

Which of the following is an assumption that is made in the kinetic theory of gases? a) Molecules make up only a small fraction of the volume occupied by a gas. b) The total number of molecules is actually very small. c) Molecules are not described by Newton's laws. d) There are forces acting on the molecules at all times. e) Molecules collide inelastically.

a) Molecules make up only a small fraction of the volume occupied by a gas.

An ideal gas undergoes a cyclic process in which total (positive) work W is done by the gas. The total heat added to the gas in one cycle is equal to a) W b) -W c) Zero d) 2W

a) W

When you make ice cubes, the entropy of the water a) decreases. b) remains unchanged. c) increases. d) decreases while the water is cooling but does not change as it turns to ice.

a) decreases.

The oxygen (molar mass = 32 g/mol) and nitrogen (molar mass = 28 g/mol) molecules in this room have equal average a) kinetic energies, but the oxygen molecules are slower. b) speeds, but the oxygen molecules have a lower average kinetic energy. c) kinetic energies, but the oxygen molecules are faster. d) speeds, but the oxygen molecules have a higher average kinetic energy. e) kinetic energies and speeds.

a) kinetic energies, but the oxygen molecules are slower.

A microwave warms up a cold piece of pizza. What type of heat transfer is this? a) Conduction b) Radiation c) Induction d) Convection e) There is no heat transfer

b) Radiation

If the thickness of a uniform wall is doubled, the rate at which heat is conducted through the wall is a) decreased by a factor of 4 b) cut in half c) unchanged d) doubled e) increased by a factor of 4.

b) cut in half