Inorganic thermodynamics

Question 1

What is 2nd law thermo

Answer 1

In a spontaneous process the entropy of the universe increases

Question 2

Entropy units

Answer 2

J per K (per mol if molar)

Question 3

give equation for molecular basis of entropy

Answer 3

S=klnW, k=Boltzmann constant, W= possible arrangement of molecules among energy levels

Question 4

Draw diagram of change of molecules arrangement in energy levels upon heating/expanding

Answer 4

see notes

Question 5

Definition of entropy?

Answer 5

dS=δq(rev)/T
If system absorbs heat entropy increases
Entropy increase is greater the cooler the object to which heat is supplied

Question 6

delta S universe =?

Answer 6

delta S surroundings+ delta S system

=delta Ssys - q(sys)/T(sys)

Question 7

When delta S univ = 0 what happens?

If it is less than 0?

Answer 7

System is at equilibrium and there is no tendency for further change
Less than 0, not allowed by second law, process won’t take place

Question 8

What is first law thermodynamics?

Answer 8

Energy cannot be created or destroyed just transformed from one form to another

Question 9

delta U =?

Answer 9

q (heat absorbed by system) + w (work done ON system)

Question 10

What is heat?

Answer 10

Means by which energy is transferred from a hotter body to a cooler one to equalise their temperatures.

Question 11

What is work?

Answer 11

Done when moving against a force

Question 12

What is internal energy

Answer 12

Possessed by an object, depends on temperature, pressure etc., it is ‘stored up’ energy, for an ideal gas all internal energy present as KE of particles (not energy of interaction between particles/chemical bond energy)

Question 13

What is a state function?

Answer 13

Takes a value depending on the state of the substance under consideration and not how that state was arrived at

Question 14

Internal energy what kind of function?

Answer 14

State

Question 15

What is a path function?

Answer 15

depends on path A–>B

Question 16

What are sign conventions for q and w?

Answer 16

q positive when heat absorbed by system, w positive when work done on system eg. when gas is compressed

Question 17

Why can’t we use Δ for path functions?

Answer 17

We can’t talk about its absolute value at state A or B

Question 18

In a gas expansion 𝛿w’ =?

Answer 18

P(ext)dV (see diagram in notes)

Question 19

Against a constant external pressure w’=?

What does this expression assume?

Answer 19

P(ext) (Vf-Vi)
Assumes throughout expansion internal pressure always greater than external pressure, need to check to make sure ( as gas expands internal pressure will fall)

Question 20

‘The work done in a reversible process…’

Answer 20

Is always at a maximum ie. internal and external pressures are only infinitesimally different and system is essentially at equilibrium

Question 21

In a reversible isothermal expansion w’=?

Conditions?

Answer 21

nRTln(Vf/Vi)

Isothermal, reversible, ideal gas

Question 22

heat involved in gas expansions, ΔU = ?

Answer 22

q-w’

Question 23

If w’ is at a max what can you say about q?

What is the consequence of this?

Answer 23

It is also at a max, ie heat absorbed is at max

Heat must be supplied to maintain the temp of gas and keep process isothermal

Question 24

Even if process is not reversible to work out dS…

Answer 24

Need to work out 𝛿q if process was reversible

Question 25

In isothermal ideal gas expansion ΔS=?

Answer 25

nRln(Vf/Vi), valid for any isothermal expansion whether or not it is reversible