True or False? Change in internal energy is directly proportional to change in temperature for all gases.

False. Change in internal energy is directly proportional to change in temperature for ideal gases.

Why do ideal gases have no potential energy?

Ideal gases have no potential energy because there are no intermolecular forces in an ideal gas.

What is the relationship between kinetic energy and internal energy for an ideal gas?

For an ideal gas, internal energy is the total kinetic energy of all the particles.

True or False? As the internal energy of an ideal gas increases, the average speed of the particles increases.

True. Internal energy is directly proportional to temperature, which is directly proportional to kinetic energy. As kinetic energy increases, so does the average speed of particles.

Define the entropy of a system.

The entropy of a system is a measure of the number of possible arrangements of the particles and their energies, i.e. it is a measure of the disorder of the system.

Put the three main states of matter in order from highest to lowest entropy.

The three main states of matter, in order from highest to lowest entropy, are: Gas (highest entropy) Liquid Solid (lowest entropy)

True or False? Entropy and temperature remain constant during a change of state.

False. Temperature remains constant during a change of state, but entropy changes .

Does entropy increase or decrease during sublimation?

In sublimation, a solid becomes a gas so entropy increases .

Does entropy increase or decrease during freezing?

In freezing, a liquid becomes a solid so entropy decreases .

Other than changing state of matter, what are two situations in which entropy can increase?

Entropy can also increase when A solid dissolves in a solvent A gas diffuses in a container

Define a reversible process.

A reversible process is one where there is no overall change in entropy as the system and its surroundings are returned to their original states.

Define an irreversible process.

An irreversible process is one that results in an increase in entropy as the system and its surroundings cannot return to their original states.

True or False? Processes occurring in real isolated systems are almost always irreversible.

True. Processes occurring in real isolated systems are almost always irreversible. The entropy of a real isolated system always increases.

Define an isolated system.

An isolated system is one in which neither matter nor energy can be transferred in or out.

How does entropy change when heat is removed from a non-isolated system?

When heat is removed from a non-isolated system, its entropy can decrease locally.

Why can the entropy of a non-isolated system decrease?

The entropy of a non-isolated system can decrease because this is compensated for by an equal, or greater increase in the entropy of the surroundings .

Define the term microstate .

A microstate is one possible arrangement of the particles in the system.

State the second law of thermodynamics.

The second law of thermodynamics states that in every process, the total entropy of an isolated system always increases.

State the second law of thermodynamics in the Kelvin form.

The Kelvin form of the second law of thermodynamics states that when extracting energy from a heat reservoir, it is impossible to convert it all into work.

State the second law of thermodynamics in the Clausius form.

The Clausius form of the second law of thermodynamics states that thermal energy cannot spontaneously transfer from a region of lower temperature to a region of higher temperature.

True or False? Heat can be converted completely into work without flowing into a cold reservoir.

False. Heat cannot be completely converted to work, this violates the Kelvin form of the second law.

True or False? Heat cannot spontaneously flow from a cold region to a warmer region.

True. Heat cannot spontaneously flow from a cold region to a warmer region.

Under what condition can heat flow from a cold region to a hot region?

Heat can flow from a cold region to a hot region when work is done on the system .

What region of a pressure-volume graph represents work done during a process?

On a pressure-volume graph, the area under a line represents the work done during that process.

What are two thermodynamic processes in which entropy does not change?

Two thermodynamic processes in which entropy does not change are: Adiabatic expansion Adiabatic compression

What are three thermodynamic processes in which entropy increases?

Three thermodynamic processes in which entropy increases are: Isobaric expansion Isothermal expansion Isovolumetric heating

What are three thermodynamic processes in which entropy decreases?

Three thermodynamic processes in which entropy decreases are: Isobaric compression Isothermal compression Isovolumetric cooling

True or False? On a pressure-volume graph, an adiabatic process is represented with a straight horizontal line.

False. On a pressure-volume graph, an isobaric process is represented with a straight horizontal line, while an adiabatic process is represented with a curve steeper than an isotherm.

What are the four steps of a simple heat engine?

The four steps of a simple heat engine are: Extract heat from a hot reservoir Use some of the extracted heat to perform work Release excess heat into a cold reservoir Return to initial state and repeat

What does the area enclosed by an engine cycle on a P-V diagram represent?

The area enclosed by a heat engine cycle represents the net work done by the engine.

True or False? A thermodynamic system following a Carnot cycle is 100% efficient.

False. A system cannot be 100% efficient, this violates the Kelvin statement of the second law (not all heat energy in can be converted to work).

What is the most efficient engine cycle theoretically possible?

The Carnot cycle is the most efficient engine cycle theoretically possible.

Name the thermodynamic process in the first stage of the Carnot cycle.

The thermodynamic process in the first stage of the Carnot cycle is isothermal expansion .

Name the thermodynamic process in the second stage of the Carnot cycle.

The thermodynamic process in the second stage of the Carnot cycle is adiabatic expansion .

Name the thermodynamic process in the third stage of the Carnot cycle.

The thermodynamic process in the third stage of the Carnot cycle is isothermal compression .

Name the thermodynamic process in the fourth stage of the Carnot cycle.

The thermodynamic process in the fourth stage of the Carnot cycle is adiabatic compression .

IBPhysicsDPHLFlashcardsThe Particulate Nature of MatterThermodynamics

Thermodynamics (DP IB Physics)

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FrontThermodynamic Systems (HL)
True or False?
Change in internal energy is directly proportional to change in temperature for all gases.
FrontThermodynamic Systems (HL)
What are the two equations for change in internal energy for an ideal gas?
BackThermodynamic Systems (HL)
The ideal gas equations for internal energy are $Δ U = \frac{3}{2} n R T$ and $Δ U = \frac{3}{2} N k_{B} T$
Where:
$Δ U$ = change in internal energy, measured in joules (J)
$n$ = number of moles, measured in moles (mol)
$N$ = number of particles
$R$ = gas constant, measured in joules per kelvin per mole (J K⁻¹ mol⁻¹)
$k_{B}$ = Boltzmann constant, measured in joules per kelvin (J K⁻¹)
$T$ = temperature, measured in kelvin (K)

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True or False?
Change in internal energy is directly proportional to change in temperature for all gases.
False.
Change in internal energy is directly proportional to change in temperature for ideal gases.
What are the two equations for change in internal energy for an ideal gas?
The ideal gas equations for internal energy are $Δ U = \frac{3}{2} n R T$ and $Δ U = \frac{3}{2} N k_{B} T$
Where:
- $Δ U$ = change in internal energy, measured in joules (J)
- $n$ = number of moles, measured in moles (mol)
- $N$ = number of particles
- $R$ = gas constant, measured in joules per kelvin per mole (J K⁻¹ mol⁻¹)
- $k_{B}$ = Boltzmann constant, measured in joules per kelvin (J K⁻¹)
- $T$ = temperature, measured in kelvin (K)
Why do ideal gases have no potential energy?
Ideal gases have no potential energy because there are no intermolecular forces in an ideal gas.
What is the relationship between kinetic energy and internal energy for an ideal gas?
For an ideal gas, internal energy is the total kinetic energy of all the particles.
True or False?
As the internal energy of an ideal gas increases, the average speed of the particles increases.
True.
Internal energy is directly proportional to temperature, which is directly proportional to kinetic energy. As kinetic energy increases, so does the average speed of particles.
State the equation for the first law of thermodynamics.
The first law of thermodynamics is $Q = Δ U + W$
Where:
- $Q$ = energy supplied to the system by heating, measured in joules (J)
- $Δ U$ = change in internal energy, measured in joules (J)
- $W$ = work done on/by the system, measured in joules (J)
What is the sign of $W$ when work is done on a gas?
When work is done on a gas, $W$ is negative.
What is the sign of $W$ when work is done by a gas?
When work is done by a gas, $W$ is positive.
What is the sign of $Δ U$ when a gas is heated and work is done on a gas?
When a gas is heated and work is done to it, its internal energy increases so $Δ U$ is positive.
What is the sign of $Δ U$ when a gas transfers heat to its surroundings and expands?
When a gas transfers heat away, $Q$ is negative and when it expands it does work so $W$ is negative. This means its internal energy decreases so $Δ U$ is negative.
A gas has 5200 J transferred to it by heating and does 2000 J of work by expanding against a piston. What is the change in its internal energy?
Using the first law of thermodynamics, $Q = Δ U + W$ , substitute the values.
$5200 = Δ U + 2000$ , work is positive because the gas expands and heat transfer is positive because it is transferred to the gas. This means internal energy is +3200 J.
True or False?
If a gas is heated, it must expand.
False.
From the first law of thermodynamics, $Q = Δ U + W$ , if a gas is heated then $Q$ is positive. However, this energy may be transferred to the system's internal energy, making $Δ U$ positive, and $W$ can be zero (no expansion) while the first law is still obeyed.
Define the entropy of a system.
The entropy of a system is a measure of the number of possible arrangements of the particles and their energies, i.e. it is a measure of the disorder of the system.
Put the three main states of matter in order from highest to lowest entropy.
The three main states of matter, in order from highest to lowest entropy, are:
- Gas (highest entropy)
- Liquid
- Solid (lowest entropy)
True or False?
Entropy and temperature remain constant during a change of state.
False.
Temperature remains constant during a change of state, but entropy changes.
Does entropy increase or decrease during sublimation?
In sublimation, a solid becomes a gas so entropy increases.
Does entropy increase or decrease during freezing?
In freezing, a liquid becomes a solid so entropy decreases.
Other than changing state of matter, what are two situations in which entropy can increase?
Entropy can also increase when
- A solid dissolves in a solvent
- A gas diffuses in a container
Define a reversible process.
A reversible process is one where there is no overall change in entropy as the system and its surroundings are returned to their original states.
Define an irreversible process.
An irreversible process is one that results in an increase in entropy as the system and its surroundings cannot return to their original states.
True or False?
Processes occurring in real isolated systems are almost always irreversible.
True.
Processes occurring in real isolated systems are almost always irreversible. The entropy of a real isolated system always increases.
Define an isolated system.
An isolated system is one in which neither matter nor energy can be transferred in or out.
State the equation for change in macroscopic entropy.
Change in macroscopic entropy is $Δ S = \frac{Δ Q}{T}$
Where:
- $Δ S$ = change in entropy, measured in joules per kelvin (J K⁻¹)
- $Δ Q$ = heat given to or removed from the system, measured in joules (J)
- $T$ = temperature of the system, measured in kelvin (K)
How does entropy change when heat is removed from a non-isolated system?
When heat is removed from a non-isolated system, its entropy can decrease locally.
Why can the entropy of a non-isolated system decrease?
The entropy of a non-isolated system can decrease because this is compensated for by an equal, or greater increase in the entropy of the surroundings.
What is the net change in thermal energy transferred for a reversible process?
For a reversible process, $Δ S = 0 J K^{- 1}$ therefore change in heat transferred $Δ Q = 0 J$ .
State the equation for a system's microscopic entropy.
A system's microscopic entropy is $S = k_{B} \ln (Ω)$
Where:
- $S$ = entropy, measured in joules per kelvin (J K⁻¹)
- $k_{B}$ = Boltzmann constant, measured in joules per kelvin (J K⁻¹)
- $Ω$ = the number of possible microstates of the system
State the equation for the change in a system's microscopic entropy.
A system's microscopic entropy is $Δ S = k_{B} \ln (\frac{Ω_{2}}{Ω_{1}})$
Where:
- $Δ S$ = change in entropy, measured in joules per kelvin (J K⁻¹)
- $k_{B}$ = Boltzmann constant, measured in joules per kelvin (J K⁻¹)
- $Ω_{1}$ = the initial number of possible microstates of the system
- $Ω_{2}$ = the final number of possible microstates of the system
Define the term microstate.
A microstate is one possible arrangement of the particles in the system.
State the second law of thermodynamics.
The second law of thermodynamics states that in every process, the total entropy of an isolated system always increases.
State the second law of thermodynamics in the Kelvin form.
The Kelvin form of the second law of thermodynamics states that when extracting energy from a heat reservoir, it is impossible to convert it all into work.
State the second law of thermodynamics in the Clausius form.
The Clausius form of the second law of thermodynamics states that thermal energy cannot spontaneously transfer from a region of lower temperature to a region of higher temperature.
True or False?
Heat can be converted completely into work without flowing into a cold reservoir.
False.
Heat cannot be completely converted to work, this violates the Kelvin form of the second law.
True or False?
Heat cannot spontaneously flow from a cold region to a warmer region.
True.
Heat cannot spontaneously flow from a cold region to a warmer region.
Under what condition can heat flow from a cold region to a hot region?
Heat can flow from a cold region to a hot region when work is done on the system.
State the condition for a process to be isovolumetric.
The condition for an isovolumetric process is $Δ V = 0$ i.e. the volume remains constant.
State the condition for a process to be isobaric.
The condition for an isobaric process is $Δ P = 0$ i.e. the pressure remains constant.
State the condition for a process to be isothermal.
The condition for an isothermal process is $Δ T = 0$ , i.e. the temperature remains constant.
State the condition for a process to be adiabatic.
The condition for an adiabatic process is $Δ Q = 0$ , i.e. no heat is transferred into or out of the system.
State the equation for work done under constant pressure.
The equation for work done under constant pressure is $W = P Δ V$
Where:
- $W$ is work done, measured in joules (J)
- $P$ is pressure, measured in pascals (Pa)
- $Δ V$ is change in volume, measured in metres-cubed (m³)
What region of a pressure-volume graph represents work done during a process?
On a pressure-volume graph, the area under a line represents the work done during that process.
What are two thermodynamic processes in which entropy does not change?
Two thermodynamic processes in which entropy does not change are:
- Adiabatic expansion
- Adiabatic compression
What are three thermodynamic processes in which entropy increases?
Three thermodynamic processes in which entropy increases are:
- Isobaric expansion
- Isothermal expansion
- Isovolumetric heating
What are three thermodynamic processes in which entropy decreases?
Three thermodynamic processes in which entropy decreases are:
- Isobaric compression
- Isothermal compression
- Isovolumetric cooling
True or False?
On a pressure-volume graph, an adiabatic process is represented with a straight horizontal line.
False.
On a pressure-volume graph, an isobaric process is represented with a straight horizontal line, while an adiabatic process is represented with a curve steeper than an isotherm.
What are the four steps of a simple heat engine?
The four steps of a simple heat engine are:
- Extract heat from a hot reservoir
- Use some of the extracted heat to perform work
- Release excess heat into a cold reservoir
- Return to initial state and repeat
What does the area enclosed by an engine cycle on a P-V diagram represent?
The area enclosed by a heat engine cycle represents the net work done by the engine.
State the equation for net work done output by the engine in terms of heat energy into the engine and heat energy out of the engine.
- The net work done by the engine is $Δ W_{o u t} = Q_{H} - Q_{C}$
  Where:
  $Δ W_{o u t}$ = useful work output of the heat engine (J)
  $Q_{H}$ = heat transferred from hot reservoir to engine (J)
  $Q_{C}$ = heat transferred from engine to cold reservoir (J)
State the equation for an engine's efficiency in terms of heat transferred into the engine and heat transferred out of the engine.
The equation for a heat engine's efficiency is $η = 1 - \frac{Q_{C}}{Q_{H}}$
Where:
- $η$ = efficiency of a heat engine
- $W_{o u t}$ = useful work output (J)
- $Q_{H}$ = total energy input from the hot reservoir (J)
- $Q_{C}$ = energy lost to the cold reservoir (J)
What is the net useful work done by the engine shown in this cycle?
The area enclosed by a heat engine cycle represents the useful work done by the engine, so the engine does 56 kJ of useful work.
What type of thermodynamic process is shown in stage A to B in the diagram below? The grey dashed lines represent isotherms.
The process from A to B is an isothermal expansion. It follows an isotherm, so is at constant temperature, but the volume is increasing.
The isothermal expansion from A to B continues from B to C, then to D, and then back to A. What kind of engine cycle is shown on this pressure-volume diagram? The grey dashed lines represent isotherms.
The diagram shows a Carnot engine cycle.
True or False?
A thermodynamic system following a Carnot cycle is 100% efficient.
False.
A system cannot be 100% efficient, this violates the Kelvin statement of the second law (not all heat energy in can be converted to work).
What is the most efficient engine cycle theoretically possible?
The Carnot cycle is the most efficient engine cycle theoretically possible.
Name the thermodynamic process in the first stage of the Carnot cycle.
The thermodynamic process in the first stage of the Carnot cycle is isothermal expansion.
Name the thermodynamic process in the second stage of the Carnot cycle.
The thermodynamic process in the second stage of the Carnot cycle is adiabatic expansion.
Name the thermodynamic process in the third stage of the Carnot cycle.
The thermodynamic process in the third stage of the Carnot cycle is isothermal compression.
Name the thermodynamic process in the fourth stage of the Carnot cycle.
The thermodynamic process in the fourth stage of the Carnot cycle is adiabatic compression.
State the equation for the efficiency of a Carnot cycle.
The theoretical efficiency of a heat engine using the Carnot cycle is $η_{C} = 1 - \frac{T_{C}}{T_{H}}$
Where:
- $η_{C}$ = maximum theoretical efficiency (Carnot cycle only)
- $T_{C}$ = temperature in the cold reservoir, measured in kelvin (K)
- $T_{H}$ = temperature in the hot reservoir, measured in kelvin (K)

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