thermodynamics (chem)

Question 1

State functions/state variables

Answer 1

Any measurable property which can be defined for a system present in a state is called state function. doesnt depend upon path followed

e.g. moles, temperature, pressure, density, mass

Question 2

Path functions

Answer 2

Quantities defined at path as well as values depending on path

Heat (Q), Work (W)

Question 3

Isothermal process

Answer 3

Temperature remains constant throughout the process
dT = 0
ΔT = _i^f∫dT = 0

Question 4

Isobaric process

Answer 4

Pressure remains constant throughout the process
dP = infinitesimally small change in P = 0

Question 5

Isochoric process

Answer 5

Volume remains constant throughout the process
dV = 0

Question 6

Adiabatic process

Answer 6

No heat exchange throughout the process
dq = 0

Question 7

Cyclic process

Answer 7

System undergoes a series of processes and finally comes back to its original state, then the process is collectively known as cyclic process

Change in state function is zero in cyclic processes

Question 8

Heat capacity of substance (c)

Answer 8

The amount of heat required/released by a substance to increase or decrease its temperature by 1 Celsius or 1K for a substance

C= dq/dT (heat req or released/ Change in temp)

unit: J/K or cal/K

Question 9

Specific heat capacity (C_s)

Answer 9

The amount of heat required/released by 1g of a substance to change its temperature by 1^oC

Heat capacity per unit mass of a substance

C_s = C/m
= dq/m dT

Question 10

Molar heat capacity (C_m)

Answer 10

intensive property (mass independent/non-additive)
Heat capacity per mole of a substance

C_m = C/n
= dq/n dT

Question 11

molar heat capacity at constant pressure, volume

Answer 11

heat capacity at
constant pressure: C_p
constant volume: C_v

molar heat capacity at
constant pressure: C_pm
constant volume: C_vm

Question 12

Relation between C_pm and C_vm for ideal gas

Answer 12

C_pm - C_vm = R (gas constant)
C_p - C_v = nR (gas constant)
C_pm/C_vm = γ (specific heat ratio)
C_vm = R/(γ -1)

only valid for molar heat capacities and not for specific heat capacity

Question 13

Internal energy (U or E)

Answer 13

• It is a state function
• It is an extensive property (mass dependent)
• for a system internal energy is the sum of all types of molecular energies as follows= KE of particles + PE of particles

Question 14

First law of thermodynamics

Answer 14

• Related to conservation of energy
• Can neither be created nor destroyed, only transformed from one form to another
• the total energy of the universe remains conserved

dU = dq + dw
ΔU = q + w

Question 15

IUPAC sign convention
1. heat given to the system
2. heat absorbed by the system
3. heat released by the surroundings

Answer 15

all +ve

Question 16

IUPAC sign convention
1. Heat given by the system
2. Heat released by the system
3. Heat absorbed by the surroundings

Answer 16

All -ve

Question 17

IUPAC sign convention
1. work done on the system
2. work done by the surroundings
3. work done by the system
4. work done on the surroundings

Answer 17

1 and 2 are +ve
3 and 4 are -ve

Question 18

Calculation of work donr

Answer 18

dW = -p_extdV
compression: dV —> -ve
expansion dV —> +ve

Question 19

irreversible work done

Answer 19

done against constant external pressure
W = -p_ext(V₂ - V₁)

Question 20

reversible work done

Answer 20

dW = P_intdV
for ideal gas
dW = -P_gdV
dW = -nRT/V dV
integrating both sides from V1 to V2

W = -2.303nRT log(V₂/V₁)
IDEAL GAS, REVERSIBLE, ISOTHERMAL WORK

Question 21

work done from graph

Answer 21

area under P-V curve

Question 22

for an ideal gas del U is a function of ___?

Answer 22

Temperature

Question 23

pressure in vacuum

Answer 23

zero

Question 24

change in internal energy for an ideal gas

Answer 24

ΔU = C_vΔT
ΔU = nC_vmΔT
ΔU = mC_vsΔT

Question 25

Enthalpy (H)

Answer 25

• form of energy
• state function
• extensive property
• for a system it is defined as the total heat (energy) content of the system and it is given as

H = U + PV

Question 26

enthalpy for ideal gas

Answer 26

H = U + PV
H = U + nRT
both U and nRT are f(t)

therefore, for ideal gas H is a function of temperature

Question 27

relation between ΔH and ΔU for gaseous species

Answer 27

ΔH = ΔU + RTΔn_g

Δn_g = n_g,p - n_g,r

Question 28

Entropy

Answer 28

• state function
• extensive property
• measure of randomness/disorderness/disturbance
• third law

Question 29

entropy of pure substance vs mixture

Answer 29

S of pure < S of mixture

Question 30

In solids, what has more entropy crystalline or amorphous

Answer 30

amorphous because crystalline substances have regular arrangement of particles

Question 31

Second law of thermodynamics

Answer 31

• Complete conversion of heat into work is not possible
• Heat cant flow from a low temp body to a high temp body without application of external help
• Spontaneous process cannot proceed in reverse direction in similar conditions
• During a sponteneous process entropy of the universe increases and at equilibrium it remains constant

ΔS (univ) >= 0

Question 32

If ΔS
1. > 0
2. = 0
3. < 0

Answer 32

1. spontaneous ΔS > 0
2. equilibrium ΔS = 0
3. non spontaneous ΔS < 0

Question 33

Third law of thermodynamics

Answer 33

At absolute zero temperature (0K) the entropy of a crystalline substance is zero

Question 34

Gibbs free energy (G)

Answer 34

• state function
• extensive property

ΔG = ΔH - TΔS