Thermodynamics

Question 1

State function

Answer 1

Depend only on state of system and not how it reached

Question 2

U changes when

Answer 2

Heat goes in or out
Work is done on or by it
Matter goes in or out

Question 3

Why is U a state func?

Answer 3

Adiabatic work W(ad) required to bring change in state = diff btw value of U in 1 state & another state
Delta U = U2-U1=W(ad)

Question 4

-ve sign for work done shows

Answer 4

Work is done on the system
U increases

Question 5

Heat

Answer 5

Exchange of energy due to temp diff

Question 6

Delta U =

Answer 6

q + w

Question 7

1st law

Answer 7

Energy if an isolated system is constant

Question 8

Pressure-volume work

Answer 8

W=P(ex) × (-dV)
= -p(ex)dV
= -p(ex)[Vf - Vi]

Question 9

Work done on a gas =

Answer 9

W = -[integral p(ex) dV]

Question 10

Reversible process

Answer 10

Ext pressure always < into pressure
P(ex) = [p(in) ± dp]

Question 11

Work in reversible process

Answer 11

W(rev) = -2.303 nRT log Vf/Vi

Question 12

Free expansion

Answer 12

Expansion of gas in vacuum

Question 13

Hange in enthalpy =

Answer 13

dU + pdV

Question 14

g in delta n(g)RT refers to

Answer 14

No of moles of (products-reactants)

Question 15

Delta H =

Answer 15

dU + d n(g)RT

Question 16

q =

Answer 16

Mc delta T

Question 17

Relation btw Cv and Cp for an ideal gas

Answer 17

Qv = CvdT = dU
Qp = CpdT = dH
dH = dU + RdT
CpdT = CvdT + RdT
Cp - Cv = R

Question 18

delta rH° =

Answer 18

Sum of enthalpies of products- sum of enthalpies of reactants

Question 19

Standard enthaply of formation

Answer 19

Standard enthalpy change fir the formation of 1 mole of a compound form its elements on their most stable states of aggregation

Question 20

Atomization enthalpy

Answer 20

Enthalpy change needed to break 1 mole of bonds to obtain atoms in gas phase

Question 21

Lattice enthalpy

Answer 21

Enthalpy change which occurs when 1 mole of ionic compound dissociated into its ions in gas state

Question 22

Born Haber cycle importance

Answer 22

Sum of enthalpy changes round a cycle is 0

Question 23

Spontaneous process

Answer 23

Irreversible process & may only be reversed by some ext agency

Question 24

Enthalpy-spontaneity relation

Answer 24

Enthalpy decrease, spontaneity increase

Question 25

Entropy

Answer 25

Degree of randomness or disorderness in the system
Higher disorder higher entropy

Question 26

What influences entropy?

Answer 26

Heat when added causes molecular motions increasing randomness
Heat added at lower temp increases entropy

Question 27

Delta S =

Answer 27

Q(rev)/T

Question 28

Delta S(total) =

Answer 28

Delta S(sys) + delta S(surr) > 0

Question 29

Delta S(tot) for reversible or irreversible?

Answer 29

Only reversible

Question 30

Gibb’s energy =

Answer 30

Delta H - T(delta S)

Question 31

Gibb’s energy & spontaneity at const P and T:

Answer 31

Delta G < 0, spontaneous
Delta G > 0, Non spontaneous

Question 32

3rd law

Answer 32

Entropy of any pur crystalline substance becomes 0 as temp becomes 0

Question 33

Delta rG =

Answer 33

Delta rH° - T(Delta rS)° = -RT ln K