11. Thermodynamics (8 lectures)

Question 1

What is thermodynamics?

Answer 1

Thermodynamics - branch of physical chemistry concerned with studying the transformations of E (heat -> work)

Question 2

What are the common units of measure in thermochemistry?

Answer 2

Question 3

What are the formulas for force, pressure, energy

Answer 3

E_KE- movement of particles

E_pot - E stored in bonds

Question 4

How to calculate the total work done when a force graph is given?

Answer 4

Integration of the graph

Question 5

How can temperature in C be converted into K?

Answer 5

Question 6

Explain thermal equilibrium and zeroth law of thermodynamics

Answer 6

Question 7

What is an intensive property?

Answer 7

Question 8

Explain the Ideal Gas Law

Answer 8

pV = nRT

Real gases show ideal gas properties (obey Boyle’s law) as p reaches 0 => example of limiting law

Question 9

What is the Ideal Gas Law based on? Explain the concept

Answer 9

Boyle’s law; Charles’s law; Avogadro’s principle:

As V is decreased - p increases

As V is increased - p decreases

As temperature increased - p increases (V unchanged)

As temperature decreases - p decreases (V unchanged)

All gases of same amount at STP are of the same volume

Question 10

Explain what are SATP conditions and what are the units of the gas constant

Answer 10

Question 11

Define the Ideal Gas

Answer 11

Question 12

Explain Dalton’s law (mixtures of ideal gases)

Answer 12

Question 13

How to calculate partial pressures in gas mixtures?

Answer 13

Question 14

How is heat, work and internal E related? (First Law of Thermodynamics)

Answer 14

Question 15

What is the difference between the system and its surroundings?

Answer 15

Question 16

What is the difference between heat and work?

Answer 16

Question 17

Explain what is work and how it relates to force

Answer 17

V1 - initial volume

V2 - final volume

Minus before the integral because - E leaves the system (w<0)

Plus before an integral would be when - E enters the system (w>0)

Question 18

What is irreversible work? Explain

Answer 18

Gas expands without any loss of heat to the surrounding

Question 19

What is mechanical equilibrium? Explain

Answer 19

The system does the least amount of work (w) when the external pressure (p_ex) is 0

Question 20

What is the relation between mechanical equilibrium and reversibility?

Answer 20

Question 21

What is isothermal reversible gas expansion?

Answer 21

Question 22

Compare and contrast the calculation and graphs of work done at constant external pressure and reversible isothermal expansion

Answer 22

Question 23

Explain heat, heat capacity and latent heat: heat is supplied to raise T

Answer 23

Question 24

How does specific heat capacity / molar heat capacity differ from heat capacity?

Answer 24

Question 25

What is internal energy?

Answer 25

Question 26

How to calculate internal energy? What is the differences between heat/work when it enters/leaves the system?

Answer 26

Question 27

What is a state function?

Answer 27

Question 28

How does the First Law of Thermodynamics related to internal E?

Answer 28

Question 29

How does the internal E change be measured experimentally?

Answer 29

Question 30

What is enthalpy?

Answer 30

Question 31

How can reactions be classified depending on enthalpy change?

Answer 31

Question 32

Define thermochemistry, what is the technique used to determine changes?

Answer 32

Enthalpy

State function - does not depend on the path taken to reach the outcome

Question 33

Name the physical phase changes in matter in endothermic and exothermic reactions

Answer 33

Question 34

Why is enthalpy of vaporisation in water high and why it is useful?

Answer 34

H bonds - many of them

Controls temperature in the planet

Question 35

What is the enthalpy of fusion? What is the opposite of it?

Answer 35

E required as heat at constant p to convert 1 mol of solid into liquid phase

Δ_fusH = .. kJ mol^-1

Enthalpy of vapourisation is the oppsoite of enthalpy of fusion

Question 36

When are the reverse reactions of the same enthalpy? How are fusion, vaporisation and sublimation related?

Answer 36

At same pressure and temperature

Question 37

Explain enthalpy of ionisation, enthalpy of e gain, lattice enthalpy change and hydration enthalpy

Answer 37

Question 38

Explain enthalpy of solution: solution, hydration and lattice

Answer 38

Question 39

What is the enthalpy of chemical change? What are the variables on which it depends?

Answer 39

Question 40

Explain enthalpy of combustion

Answer 40

Excess O₂

_{Reaction produces heat and work (example)}

Question 41

Explain what is Hess’s law

Answer 41

Question 42

What is the driving force of spontaneous / non-spontaneous reactions?

Answer 42

Spontaneous - tendency of matter to be disordered

Non-spontaneous - work

Question 43

Explain the disperse of E and the idea behind it

Answer 43

Question 44

Explain the Second Law of Thermodynamics

Answer 44

Question 45

What is the equation to measure entropy chnage? Explain why ΔS is proportional to q, inversely proportional to T and q_rev used

Answer 45

• proportional to q because - transfer E as heat increases the random motion of particles → increase in disorder
• inversely proportional to T because - if object is hot the change in disorder will be less significant than the change in disorder in a cold object
• q_rev because - the studied system is in thermal and mechanical equilibrium - the distribution of matter is not random

Question 46

Explain Trouton’s rule, wht are NH₃ and H₂O different?

Answer 46

Question 47

What are the possible ways to change entropy in a system?

Answer 47

1. Change in V (ΔS = nRln(V₂/V₁) = -nRln(p₂/p₁) )
2. Phase transition (ΔS = q_rev / T = ΔH_tr / T_tr )
3. Heating (ΔS = cln(T₂/T₁) )

Question 48

What object could have an entropy value of 0? State the Third Law of Thermodynamics

Answer 48

A perfectly ordered system, ex a solid crystal at 0 K temp

IN reality perfect crystal cannot be achieved

Question 49

Explain standard reaction entropy and its formula

Answer 49

Question 50

Explain entropy of mixing

Answer 50

Calculated by the expansion formula for

ΔS = nRln(V1/V2)

Question 51

Entropy change in a system vs in surrounding

Answer 51

• Entropy change in system: entropy of mixing
• Entropy change in surrounding: E transfer from system to surrounding (ex as heat)

Question 52

What is the enthalpy of the universe? How does it determine spontaneity of a reaction?

Answer 52

Enthalpy of the universe is equal to the sum of enthalpies for the system and its surrounding

ΔS > 0 → irreversible spontaneous reaction

ΔS = 0 → reversible change (at equilibrium)

ΔS < 0 → irreversible non-spontaneous reaction (sito nesake taip tiesiogiai, deducinau)

Question 53

Whats is Gibbs energy used for?

Answer 53

To describe spontaneity of a process at a constant temperature and pressure

Question 54

Explain Gibbs energy and the meanings of its values

Answer 54

Question 55

What is the standard Gibbs energy change? What conditions must be met for it to be standard?

Answer 55

Question 56

What is phase transition and what does Gibbs energy equal to?

Answer 56

• Phase transition: transitions between allotropes, (ex tin pest: beta tin to alpha tin; maleable form to brittle)
• Gibbs E at phase change = 0 → equation can be used to determine temperature

Question 57

How does Gibbs energy change through the reaction?

Answer 57

Question 58

How should the graph of Gibbs E diagram be interpreted for a reaction?

Answer 58

Question 59

When is a system at equilibrium?

Answer 59

No tendency to spontaneously occur in neither direction

Question 60

What does the value K tell about the reaction?

Answer 60

Question 61

How does Q and K of a reaction relate?

Answer 61

Question 62

What is the effect of tempreature on equilibrium constant K?

Answer 62

As themperature is raised → K increases because more products are formed (K = [products]/[reactants])

Question 63

What does the van’t Hoff equation do?

Answer 63

Allows to calculate K₂ at a different T₂ when K₁ and T₁ is known

Question 64

How can van’t Hoff equation be used to predict K value when temperature is altered in an endothermic process?

Answer 64

In exothermic the opposite

Question 65

Is K dependent on pressure?

Answer 65

No but change in pressure changes the position of equilibrium in the reaction (K is a constant)