Thermodynamics

Question 1

What are the forms of energy?

Answer 1

1. Kinetic energy
2. Potential energy

Question 2

What is kinetic energy?

Answer 2

The energy that an object or a system possesses due to its motion

Question 3

Whats kinetic energy and its formula?

What is it related to?

Answer 3

For a particle with mass, m, and a velocity, v, we can evaluate the kinetic energy as:

E_kin= 1/2 MV²

Kinetic energy is related to temperature

Question 4

Whats potential energy?

Answer 4

The stored energy in an object or system due to its position or configuration

Question 5

Whats chemical bond energy?

Answer 5

Chemical bond energy is the energy stored in chemical bonds

Question 6

Tell me if the following release or require energy?

• bond formation
• bond cleavage

Answer 6

Bond formation releases energy

Bond cleavage requires energy

Question 7

What are the 3 forms of system?

Answer 7

1. open system
2. closed system
3. isolated system

Question 8

Whats an open system?

Answer 8

Both matter and energy can be transferred between the system and the surroundings

Question 9

Whats a closed system ?

Answer 9

Only energy can be transferred between the system and the surroundings

Question 10

Whats an isolated system ?

Answer 10

Neither matter nor energy can be transferred between the system and the surroundings

Question 11

Whats the simplest system?

Answer 11

Isolated system is the simplest system

Energy and contents in isolated system is constant

Question 12

Whats the 1st law of thermodynamics?

Answer 12

The sum of energies of a system and its surroundings remain constant

• energy cannot be created or destroyed
• energy can only be transferred between different forms

Question 13

Give a real world example of the 1st law of thermodynamics?

Answer 13

Real world example of this:

• Dam (or waterfall). Raises the water level of the river to create falling water. The reservoir that is formed is, in effect, stored energy.
• Turbine. The force of falling water pushing against the turbine’s blades causes the turbine to spin. The turbine converts the kinetic energy of falling water into mechanical energy.
• Generator. Connected to the turbine by shafts. When the turbine spins the generator will also spin, converting the mechanical energy from the turbine into electrical energy

stored (potential) energy → kinetic energy → mechanical energy → electrical energy

Question 14

The energy derived from pressure and volume change is given by what?

Answer 14

E= pV (a type of work)

Question 15

Define enthalpy, H?

Answer 15

H= U + pV

Question 16

Whats the formula for the change of enthalpy of a system?

Answer 16

∆H= ∆U + ∆(pV)

Question 17

since in biology most measurements are made at constant pressure, p=p_const we can assume there is no change in p. Therefore…?

Answer 17

∆ (pV) = p∆V (for constant p)

Question 18

Whats the formula for internal energy?

How can work be described? With this define ∆H?

Answer 18

∆U = w + q

w= -∆(pV)

w= p∆V

therefore;

∆H= w + q + p∆V

∆H= -p∆V + q + p∆V

∆H= q

Question 19

Whats an endothermic reaction?

Answer 19

• Heat flowing into a system from its surroundings is defined as positive, (+q)
• A process that absorbs heat from the surroundings is called endothermic.
• So, the system gains heat, the surroundings cool down.

Question 20

Whats an exothermic reaction?

Answer 20

• When the heat flows out of the system into the surroundings, the heat flow is given a negative value (-q)
• A process that gives heat to the surroundings is called an exothermic process.
• The system loses heat, whereas the surroundings heat up.

Question 21

Give an example of a real world example of an endothermic and exothermic reaction?

Answer 21

Ice melting= endothermic process

Explosion= exothermic process

Question 22

Whats the 2nd law of thermodynamics?

Answer 22

In an isolated system the entropy can only ever increase.

If i have a closed system, I need to evaluate the entropy of the system and the surroundings

Question 23

What are the quantities describing a system and examples?

Answer 23

Macrostates: Temperature, Pressure, Volume

Microstates: Kinetic energy, Force, Velocity

e.g. assign mass, velocity, position for any particle in a system at any time

Question 24

What can macrostates be described as?

Answer 24

A collection of microstates

Question 25

Whats the definition of equilibrium?

Answer 25

Macrostates do no change over time (necessary condition for macrostate to be well-defined) In contrast microstates can be specified at any time

Question 26

Whats entropy, S?

Answer 26

It is defined by the number of microstates, Ω, of a system

Question 27

Whats the number of microstates at a given total energy described as?

Answer 27

Ω(E)

Question 28

The Boltzmann constant is: kB = 1.38064852 × 10-23 m² kg s^-2 K^-1 Whats the formula relating entropy and the boltzmann constant?

Answer 28

S= K_B ln(Ω)

Question 29

What does the microscopic state refer to?

Answer 29

The exact states of all the molecules making up the system

Question 30

Whats the formula for Clausius inequality?

Answer 30

∆S ≥ ∆q/T ∆q= heat exchange T= temperature of the heat exchange

Question 31

Describe ∆q in either reversible or irreversible processes?

Answer 31

∆q in reversible process: ∆S= ∆q/ T (this is the definition of entropy) ∆q is irreversible process: ∆S \> ∆q/T

Question 32

Whats the formula for gibbs free energy?

Answer 32

∆G= ∆H - T∆S

Question 33

For a reaction to be spontaneous, what must ∆G be?

Answer 33

negative

Question 34

Whats the formula for the relation between ∆G and the equilibrium constant, K_c?

Answer 34

Question 35

Example reactions

Answer 35

Question 36

Whats the **Chemical potential,µ,** of the system?

Answer 36

The free energy per mole of that compound under a given set of conditions

Question 37

What is µ also referred to as?

Answer 37

The partial molar Gibbs free energy

Question 38

Chemical potential is an intensive state function that is independent of the system size. What is meant by a state function?

Answer 38

a quantity in thermodynamics, such as entropy or enthalpy, that has a unique value for each given state of a system

Question 39

The useful measure of the average energy of a molcule depends only on what?

Answer 39

environment, not system size

Question 40

Whats the chemical potetial definition for a one component system?

Answer 40

**µ= G/n** OR **G= µn** (n is the number of moles)

Question 41

Whats the chemical potetial definition for a multicomponent system?

Answer 41

**G= ∑_xµ_xn_x** It is the sum of the chemical potentials of all the species present

Question 42

The change in free energy for removal of reactants is described as what?

Answer 42

Here ∆n is negative (nunber of moles of reactant is decreasing)

Question 43

The change in free energy for addition of products is described as what?

Answer 43

Here ∆n is positive (number of moles of product is increasing)

Question 44

Whats the equation for the sum of two expressions to get the overall change in free energy?

Answer 44

Question 45

Complete this calculation... Given the chemical potentials of ATP, AMP, Pi and H2O, what is the free energy change for the hydrolysis of one mole of ATP to AMP?

Answer 45

Question 46

Here is a simple reaction; **A⇔B** Use this equation to write the free energy equation? How will the reaction be spontaneous?

Answer 46

**A⇔B** This can be written as; **∆G = µ_Bn - µ_An** If µ_B is less than µ_A, then ∆G will be negative and the reaction will be spontaneous: as the µ_B and µ_A are positive Here the criterion for spontaneous change is lowering of the chemical potential. Equilibrium occurs when the chemical potentials are equal **(µB=µA​)**

Question 47

For this complex reaction; aA + bB ⇔ cC + dD Whats the equation for the free energy? What are the conditions for a spontaneous change?

Answer 47

Free change energy is given by: **∆G= µ_x∆n_x= cµ_c + dµ_D - aµ_A - bµ_B** For a spontaneous change **cμc + dμD must be less than aμA + bμB**

Question 48

What is a spontaneous change?

Answer 48

The weighted sum of the chemical potentials can be lowered

Question 49

Whats an equilibrium?

Answer 49

The weighted sums of chemical potentials for reactants and products are equal

Question 50

Whats the equation that relates free energy of an ideal gas to its pressure?

Answer 50

**G=G° + nRTlog(P/P°)**

Question 51

Whats the equation for a pure compound that relates the free energy of an ideal gas to its pressure?

Answer 51

Recall that μ for a pure compound is equal to G/n **μ =μ°+ RTlog(P/P°)** ⇒ divided the above equation by n to get this

Question 52

The equation for µ can be extended to one component of a mixture of ideal gases, what is this equation?

Answer 52

**μ =μ_x°+ RTlog(P_x/P°_x****)** Here P_x is the partial pressure of x (the pressure exerted by x). The total pressure would be the sum of the partial pressures of all different gases in the mixture

Question 53

is free energy dependent on concentration?

Answer 53

yes

Question 54

Consider the multi-component reaction; aA + bB ⇔ cC + dD Whats the equation that describes the relationship between the free energy and the change in concentration of the components?

Answer 54

Question 55

For convenience, the term [Product]/[reactants] is often referred to as the **mass action ratio.** What symbol is this given ?

Answer 55

it is given the symbol, Γ

Question 56

Whats the equation for free energy, involving the mass action ratio, when the reaction is not in equilibrium?

Answer 56

**ΔG=ΔG° + RTlog_eΓ**

Question 57

At equilibrium, ∆G=0, the mass action ratio at equilibrium is called the equilibrium constant, K. Whats the equation for free energy now?

Answer 57

**ΔG°= -RTlog_eK**

Question 58

What are the units for K and Γ?

Answer 58

They don't have units

Question 59

Are Log_e and ln equal?

Answer 59

yes

Question 60

Recall that the equilibrium constant of a reaction also varies with temperature (the position of the equilibrium is affected by temperature). We have also seen the following equations, combine then to work out Log_eK?

Answer 60

Question 61

Draw the graphs for the exo- and endothermic reactions with Log_eK on the y-axis and 1/T (1/K) on the x-axis. Whats the gradient? Whats the intercept?

Answer 61

* Should produce a straight line * Negative slope for -∆H˚/R, then it is an endothermic reaction * Positive slope for -∆H˚/R, then it is an exothermic reaction * Never really hit zero and otherwise it’s a very high temperature being used * Intercept corresponds to infinite temperature

Question 62

Whats the **Van't Hoff isochore?**

Answer 62

Question 63

How can the total free energy, ∆G, of a system be obtained?

Answer 63

By adding together the chemical potentials multiplied by the amount of all the components of the system

Question 64

The variation of ∆G with concentration for a reaction is related to what?

Answer 64

The mass action ratio