Thermo Flashcards

1
Q

Isolated systems?

A

Don’t allow transfer of mass or energy in or out

e.g. thermos flask

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2
Q

Closed systems?

A

Allow transfer of energy in or out but mass remains constant
e.g. gas in a cylinder

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3
Q

Open systems?

A

Mass and energy can be transferred in or out
e.g. centrifugal compressor

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4
Q

Intensive properties?

A

Properties which are independent of mass/system size

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5
Q

Examples of intensive properties

A

Temp, density, pressure, specific enthalpy

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6
Q

Extensive properties?

A

Properties which are dependent/proportional to mass or system size

Can be converted to intensive by dividing one property by another e.g mass/vol = density
total energy/mass = specific energy

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7
Q

Examples of extensive properties

A

Volume, internal energy, enthalpy

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8
Q

State variables?

A

Describe state of the matter @ equilibrium

Independent of the path to reach them

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9
Q

Examples of state variables

A

Temp, pressure, vol, entropy, mass

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10
Q

Isothermal process?

A

System changes without temp changing

Remains in thermal equilibrium

e.g. refrigerator

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11
Q

Isobaric process?

A

System changes without pressure changing

e.g. boiling water to steam

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12
Q

Isocharic process?

A

System changes without volume changing

e.g. ideal Otto cycle / a pressure cooker

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13
Q

Adiabatic process?

A

System changes without any heat or energy transfer occuring

e.g. piston in car engine

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14
Q

Process functions?

A

Describe the route to move away from equilibrium, depend on path

Give finite amounts, rather than a change, when integrated

e.g. work, heat

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15
Q

Zeroth law of thermo?

A

When two objects are separately in thermal equilibrium with a third, they are all in thermal equilibrium

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16
Q

Examples of sources of potential energy within a system

A

-Attractive and repulsive forces
-Sub-molecular energy associated with nuclei and electrons e.g. bonds

17
Q

First law of thermo?

A

Energy can’t be created or destroyed

18
Q

How are irreversible and reversible processes shown on a PV plot?

A

-Irreversible are shown as a dashed line, as the intermediate steps between the initial and final states are not in equilibrium
-Reversible are a solid line as the system passes through a set of equilibrated states, but is generally a slow process

19
Q

What are irreversible processes?

A

Those which can’t return to a previously equilibrated state by simply reverting back to the original conditions

20
Q

What are reversible processes?

A

Those where you can move from one equilibrated stater to another (quasi-statically) by simply altering the conditions of the system

21
Q

What is the entropy change of any system and its surroundings, when considered together?

A

-Gives a positive value
-Approaches zero when the process approaches reversibility

22
Q

What is the 2nd law of thermo?

A

For an irreversible process the combined entropy of the system and environment will increase

23
Q

What are the 4 steps of a carnot cycle/engine

A

1) Isothermal process
2) Adiabatic process
3) Reverse isothermal process
4) Reverse adiabatic process

24
Q

What is a carnot engine

A

-A reversible engine, dS = 0`
-Able to create work
-If run backwards, it requires work (refrigeration)