Chapter 4 - First Law of Thermodynamics

What is a thermodynamic system

A fixed amount of substance or volume of space that forms the subject of investigation

What are the two type of thermodynamic systems

Open or closed

What is the condition for a closed thermodynamic system

No substance is allowed to flow in or out

What does an open thermodynamic system allow

Transfer of mass

How is a thermodynamic system distinguished from its surroundings

A system boundary

The boundary of a system can either be

Real or imagined

What type of boundary does a closed thermodynamic system have (including 2 subtypes)

An impermeable thermodynamic wall which is either fixed or dynamic

How is a open thermodynamic system bound

By a control volume which can include impermeable thermo dynamic walls

What is an impermeable thermodynamic wall

A boundary which does not allow mass though

What are the two types of thermodynamic walls

Adiabatic and a diathermal wall

What is a adiabatic wall

A wall that does not allow heat transfer

What is a diathermal wall

It allows heat transfer

What type of wall is said to be thermally isolated

Closed adiabatic

What kind of wall is said to be in thermal contact

diathermal

What is the state of a thermodynamic system defined by

Its thermodynamic variables

What are the two kinds of thermodynamic properties

Intensive and Extensive

What is an intensive property

They are defined at any given point within a system, it does not change will mass or size

What is a example of a intensive property

Temperature/pressure/density

What is an extensive property

It reflects the system size

What is an example of an extensive property

Mass/volume

How can extensive properties be made into intensive variables, and what are these variables called

By dividing by the mass, specific properties

When is a system in thermodynamic equilibrium

When the variables are not changing with time

When are two system in thermal contact in thermal equilibrium

When there is no heat transfer between them, they are at the same temperature

When are two systems in mechanical contact said to be in mechanical equilibrium

When there is no exchange of work between them, when they are both at equal pressure

When is a system in chemical equilibrium

When the chemical composition does not change, there is no chemical reactions

When is a system in phase equilibrium

When the mass of each phase reaches an equilibrium level and stays there

What does the state postulate say

How many independent properties are needed to uniquely define the state of a system

How can the state of a simple compressible system be given according to the state postulate

The state of a simple compressible system is completely specified by two independent intensive properties

What is a process

A sequence of changes

What is an isothermal process

A process at a constant temperature

What is an Isobaric process

A process at a constant pressure

What is an isochoric process

A process at a constant volume

What is a cyclic process

A sequence of process which return a process to its initial state

What is a quasi static process

A process that takes place infinitely slowly so that the system passes through a continuous sequence of equilibrium states

What is a pure substance

A substance with a homogeneous chemical composition through out the whole thermodynamic system

What do the relationships between properties in equilibrium

The kind of substance and the phase

What type of substance can air be considered as

Pure

In what conditions does the ideal gas law hold true

Moderate temperatures and low pressures

What 2 observations does the ideal gas law come from

Boyles law and charle’s law

What is Boyle’s Law

The volume of a fixed mass of gas at a constant temperature

What is Charle’s Law

The volume of a fixed mass of gas at a constant temperature is proportional to its pressure

What is an ideal gas

A gas which obeys the ideal gas law

What is an isotherm

Curves along which the temperature stays constant

What is an isochore

Curves along which the specific volume stays constant

What is an isobar

Curves along which pressure stay constant

What does the zeroth law of thermodynamics state

Every thermodynamic system in equilibrium has a property called temperature and two systems in thermal equilibrium if and only if they have the same temperature

What does the ideal gas temperature scale define

An absolute zero at which an ideal gas would have zero pressure

What is the triple point of water

The temperature and pressure at which the solid liquid and vapor phases of water can coexist in mutual equilibrium

What is heat

Energy transferred between a system and its surroundings due to temperature difference

Is heat positive or negative when transferred into the system

Positive

Is heat positive or negative when transferred out of the system

Negative

What is work

Energy transfer between a system and the surroundings that does not involve heat

When work is done on a system is is positive or negative

Positive

When work is done by system is is positive or negative

Negative

What is a P-V system

A system with the primary interest being pressure and volume

What is a referable process

When a system and its surrounding’s can be resorted to their original state with no net transfer of work

What are the conditions for reversible work in a P-V system

Frictionless and the pressure difference between the system and the surroundings must be infinitely small so quasi static

What are two examples of a boundary phenomena

Heat and work

Why are heat and work boundaries phenomena

As they cross the systems boundary

What type of functions are heat and work and why

Path as their magnitudes depend on the path followed not just the end state

What kind of functions are properties

Point

What is work done graphically

The area under a P V curve

How is the path of an irreversible process depicted on a graph

As a dashed line

How do you use this equation

Get P in terms of v using ideal gas law and integrate between the two pressures

Give a statement about amount of work in a reversible process

Reversible processes maximise the amount of work that my be done by or on a system

What do the process paths for a cyclic process do

Form a closed path

What makes a cyclic process a reversable one

When each subpath is reversible

Work is done by the system if the path C is traversed in….

Clockwise direction

Work is done on the system if the path C is traversed in…

Anticlockwise direction

In a P-V system, what is the work done equal to

Area enclosed by the closed path

What is internal energy

The total energy in a thermodynamic system

What does internal energy depend on

The state of the system only

What is an Ideal monatomic gas

A gas where particles are single atoms

What does internal energy of a system not include and why

Potential or kinetic energies as these are external

What is heat capacity

The ratio is head supplied to the change in temperature

What does heat capacity depend on

Type of substance and the process by which heat is added

What is specific heat capacity

The energy needed to raise a 1kg substance by 1k

When a gas is heated at a constant pressure, what happens to some of the heat energy

It is used to perform work to expand

What is an isothermal process

One at a constant temperature

What are isotherms

Paths for isothermal processes on a graph

What happens in a gas expansion if the gas is thermally isolated, and what about the work done

Heat transfer is not possible so it expands adiabatically

Tell me about work done in adiabatic expansion

When a gas expands adiabatically the work it does comes directly out of its internal energy, so the gas cools down

What is an adiabatic process

Where there is no heat exchange between a system and its surroundings

What is a adiabatics

Paths for a adiabatic process

What are isothermal and adiabatic expansions examples of

Polytrophic expantions

What is a polytrophic process

One where pressure and volume are related by the polytrophic equation of state

What is n

The polytrophic index

What is n for an isobaric process

0

What is n for an isothermal process

1

What is n for an adiabatic process

gamma