Chemical Thermodynamics

Question 1

Define Internal Energy

Answer 1

Total Capacity of a system to do work

Question 2

Translational Motion (Equation)

Answer 2

Etrans = 1/2*mv^2

Question 3

Rotational Motion (Equation)

Answer 3

Erot = 1/2*Iw^2, where w is the rotational frequency and I is moment of inertia

Question 4

Equipartition Theorem

Answer 4

Etotal for each mode of motion per mole of molecules = (1/2)RT

Question 5

Avg KE (Degree of Freedom for one molecule)

Answer 5

(1/2)kT, where k is the boltzmann constant

Question 6

Translational contribution (Gases)

Answer 6

A gas molecule has translational contribution to internal energy (U) per mole = (3/2)RT

Question 7

Rotational Contribution (Linear Molecule)

Answer 7

Linear molecules rotate about any two axis perpendicular to bonds therefore the rotational contribution = RT

Question 8

Rotational Contribution (Non-linear molecule)

Answer 8

Molecules rotate about three axis therefore rotational contribution = (3/2)RT

Question 9

First Law of Thermodynamics

Answer 9

The internal energy of an isolated system is constant meaning deltaU = 0

Question 10

Work & Heat

Answer 10

w = work
q = heat
If w +ve work done on system and -ve if done by.
If q +ve heat supplied to system and -ve if released by.

Therefore: deltaU = w + q

Question 11

Types of work

Answer 11

Expansion (Changes in Volume)

Non-Expansion (No change in Volume)

Question 12

Irreversible Expansion (equation)

Answer 12

w = Pex*deltaV

Equation is negative if work is done by gas

Question 13

Reversible expansion (equation)

Answer 13

Wrev = nRT*ln(Vf/Vi) where it is negative if work is done by gas.

At constant Temperature, area under Boyle’s curve

Question 14

Calorimetry

Answer 14

Insulated container so that any change in heat by reaction is directly related to change in temperature of water.

As insulated, flow of head is directly proportional to internal energy change.

Delta U = -Ccal*deltaT

Negative as heat being released

Question 15

Introducing Enthalpy with Internal Energy

Answer 15

H = U + pV

At constant pressure, Delta H = q
Delta H = H(Products)-H(Reactants)

Question 16

Heat Capacity

Answer 16

1) Heating causes changes in Temperature

2) Different substances heated at T do not give same dT

Question 17

Heat Capacity (Definition)

Answer 17

Heat Capacity, C, of object measures how much heat must be supplied to raise the temperature by a given amount.

Question 18

Specific Heat Capacity (Cs)

Answer 18

Cs = q/m*dT

This relates to 1g of an object

Use g not Kg in this equation

Question 19

Specific Heat Capacity (Cm)

Answer 19

Cm = q/n*dT

This relates to moles

Question 20

General Heat Capacity (equation)

Answer 20

C = q/dT

Question 21

Enthalpy Change (Definition)

Answer 21

dH is the heat transferred by a chemical reaction at constant pressure

Question 22

Molar Enthalpy of Melting

Answer 22

dH which occurs when 1 mol of a solid melts to form a liquid

Question 23

Molar Enthalpy of Vaporization

Answer 23

dH which occurs when 1 mol of liquid boils to form a gas

Question 24

Open System and Constant Volume (Enthalpy Change Equation)

Answer 24

dH = dU + p*dV

Question 25

Hess’s law

Answer 25

drH = Sum of all drH

drH = Sum(dfH(products)) - Sum(dfH(reactants))
drH = Sum(bonds broken) - Sum(bonds formed)

Question 26

Kirchoff’s Law

Answer 26

Heat Capacity at const. pressure = drH[T2] = drH[T1] + dCp(T2 - T1)

Question 27

Second Law of Thermodynamics

Answer 27

Spontaneous processes are those that increase the total entropy of the universe

Question 28

Third Law of Thermodynamics

Answer 28

The entropy of a perfect crystal is zero at T=0K

Question 29

Entropy

Answer 29

dS = dS(system) + dS(surroundings)

if dS > 0 spontaneous, if < 0 then non spontaneous and if =0 then process is at equilibrium

Question 30

Entropy with dT (NOT GIVEN IN EXAM)

Answer 30

S[T2] = S[T1] +Cv*ln(T2/T1)

Question 31

Phase Transition in terms of entropy

Answer 31

dS = dH / T

Question 32

Crystal Disorder

Answer 32

Disorder due to possible rotations therefore residual entropy. Where, S = Kb*lnW, where W = 2Na for 2 molecules.

Where Kb is the boltzmann constant