Thermodynamics

Question 1

Whats the formula for the total internal energy of a system and what does each symbol stand for?

Answer 1

U = w + q

U= total energy of a system

w= work

q= heat

Question 2

What are the forms of energy ?

Answer 2

1. kinetic energy
2. potential energy

Question 3

Whats the formula for kinetic energy and what does each symbol represent?

Answer 3

E_kin= 1/2 MV²

m= mass

v= velocity

Question 4

Whats are the two types of potential energy?

Answer 4

1. gravitational potential energy
2. chemical bond energy

Question 5

What are the 3 types of system?

Answer 5

1. Open system: Both matter and energy can be transferred between the system and surroundings

2. Closed system: only energy can be transferred between the system and surroundings

(overtime an equilibrium forms in a closed system)

3. Isolated system: Neither matter nor enegry can be transferred between the system and the surroundings

Question 6

What is the first law of thermodynamics? what does this mean?

Answer 6

Conservation of energy

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

• energy cannot be created nor destroyed
• Energy can only be transferred between different forms

Question 7

Whats the formula for work?

Answer 7

work = force x distance

Question 8

According to Newton, what does force equal?

Answer 8

Force= mass x acceleration

Question 9

Whats coulombs law and what do the symbols represent?

Answer 9

F = Kq₁q₂/ r²

K= coulombs constant

q₁ and q₂ are the magnitudes of the charges (+ for positive and - for negative

r= distance between the two charges

Question 10

Whats the universal observation of energy transfer as heat?

Answer 10

A hot system in contact with colder surroundings will spontaneously get colder

HOWEVER: the reverse process will not happen (e.g. hot systems in contact with colded surroundings will not get hotter)

Question 11

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

Answer 11

E = P x V

Question 12

Whats the definition for the change in enthalpy?

Answer 12

∆H = ∆U + p∆V

Question 13

Whats the definition for an endothermic reaction?

Answer 13

Any process which requires or absorbs energy from its surroundings, usually in the form of heat

∆H> 0 (positive)

Question 14

what the definition of an exothermic reaction?

Answer 14

A chemical reaction that releases energy through light or heat

∆H < 0 (negative)

Question 15

What are the standard conditions and what are they denoted by?

Answer 15

ø = 298 K and 1 atm/ 1 bar

Question 16

How can enthalpy changes be measured in a closed system?

Answer 16

using a abomb calorimeter

Question 17

What is the second law of thermodynamics?

Answer 17

In an isolated system, the entropycan only ever increase

(if I have a closed system, I need to evaluate the entropy of the system and the surroundings)

Question 18

What is the definition of Entropy?

Answer 18

entropy,s, is defined as the number of microstates of a system

Question 19

Whats the formula for entropy, using the boltzmann constant and microstates (being defined as omega)?

Answer 19

S= K_B ln(omega)

Question 20

Whats the change in entropy proportional to?

Answer 20

The change in entropy is proportional to the heat transferred from the system to the surroundings

Question 21

Give the formula for entropy relationship with temperature and heat. What are the units?

Answer 21

∆S ≥ ∆q /T

∆q= joules, J

T= Kelvin, K

Question 22

What does -∆S equal to with respects to heat and temperature?

Answer 22

-∆S = ∆H_surroundings /T

Question 23

What happens to entropy in the system and in the surroundings in an exothermic reaction?

Answer 23

In an Exothermic reaction, the entropy of the system decreases but the entropy of the surroundings increases as energy is transferred from the system to the surroundings

∆H_system<0

Question 24

What happens to entropy in the system and in the surroundings in an endothermic reaction?

Answer 24

In an endothermic reaction, the entropy of the system increases but the entropy of the surroundings decreases as energy is transferred from the surroundings to the system

∆H_system > 0

Question 25

What are the conditions for a reaction to be able to occur spontaneously?

Answer 25

**∆S_total = ∆S_system + ∆S_surroundings \>0** for a reaction to occur spontaneously, the total entropy of the system and the surroundings need to increase

Question 26

What is the equation for **Gibbs free energy** and the units of the components?

Answer 26

**∆G = ∆H - T∆S** ∆G= Gibbs free energy ( J mol-1) ∆H= Enthalpy (J mol-1) T= Temperature (kelvin) ∆S= entropy (L K-1 mol-1) **Need to divide by 1000 when doing calculations so units are KJ K-1**

Question 27

What are the quanities that describe a system and what do these represent?

Answer 27

**Macrostates:** temperature, pressure, volume (things you can measure on whole system e.g. thermometer for temperature etc.) **Microstates:** Kinetic energy, force, veolcity...

Question 28

What can macrostates be descirbed as?

Answer 28

a collection of microstates

Question 29

Whats the definition for **equlibrium?**

Answer 29

macrostates do not chnage over time (necessary condition for macrostates to be well-defined)

Question 30

In isolated system **in a thermal equilibrium**, whats likely? In an isolated system **out of thermal equilibrium**, how does it evolve?

Answer 30

**In thermal equilibrium:** all microstates are equally likely **Out of thermal equilibrium:** It will evolve irreversable towards equilibrium

Question 31

Whats the fomula describing the probability of any number of particles in a system?

Answer 31

**P(N,N_L) = N! / (N-N_L)! x 1/2^N**

Question 32

whats the **hydrophobic effect?**

Answer 32

The observed tendancy of nonpolar substances to aggregate in aq solution and exclude water molecules

Question 33

What are the most common functions of the hydrophobic effect in biological systems?

Answer 33

* it stabalises the phospholipid membranes and hence the formation of cells and cellular components * it drives proteins to fold into the 3D strucuture and hence be able to function

Question 34

Whats the basic structure of a phospholipid, what is it comprised of?

Answer 34

Question 35

Why do mixed substances have more microstates?

Answer 35

They can be arranged in a greater number of ways

Question 36

if ∆G\>0, then is the solution more likely to mix or not to mix

Answer 36

The equilibrium is towards the demixed state. so mixing in the solution is less likely

Question 37

if ∆H is close to 0, is this mixture likely to mix or not?

Answer 37

it is more likely to mix the closer to 0 it is

Question 38

if T∆S is large and negative, is the mixture more likely to mix or not?

Answer 38

If T∆S is large and negative, entropy is driving the reaction towards demixing this is counterintuitive as mixing two moleucles in a solution would be entropically favourable

Question 39

From experiments we know that in liquid water, a water molecule has on average 4 neighbours and forms two H-bonds. How many microstates are there in water?

Answer 39

6

Question 40

If one corner is occupied by a hydrocarbon atom that doesnt allow the formation of H-bonds, the central molecule can now only form how many microstates?

Answer 40

3

Question 41

How does introducing hydrocarbons to water... 1. explain phospholipid membrane assembly? 2. explain the hydrophobic collapse in protein folding

Answer 41

1. minimising the exposure of hydrocarbon chains to water, minimises the entropy of water in the presence of a phospholipid 2. minmising the exposure of hydrocarbon containing sidechains to water maximises the entropy of water

Question 42

What is the formula for Gibbs free energy?

Answer 42

∆G= ∆H - T∆S

Question 43

whats the conditions for a spontaneous reaction, with reference to Gibbs free energy?

Answer 43

∆G\< 0

Question 44

How do you work out if ∆G\<0? What happens is ∆G is potive?

Answer 44

To calculate if ∆G\<0... **∆G= G_products - G_reactants** If the reaction is positive then it will occur in the opposite direction

Question 45

What does the amount of ∆G transferred from the system to the surroundings determine?

Answer 45

The free energy that is available to do work

Question 46

What does ∆G⁰ mean?

Answer 46

That its at a standard state and the value doesn't change

Question 47

whats does ∆G=0 mean?

Answer 47

that the reaction is in equilibrium

Question 48

consider the reaction; **-aA + bB ⇔ cC +dD** Write the K_c equation for this and Kc general formula. why is Kc written this way and what does it mean?

Answer 48

If you divide by the compounds in standard states then K_c becomes dimensionless (no units)

Question 49

In K_c what type of number would you get in the following situations... 1. if the products are smaller than the reactants 2. If the products are bigger than the reactants 3. If the products are an equal size to the reactants

Answer 49

_{1. Kc would be a s​mall number 2. Kc would be a big number 3. some intermediate number}

Question 50

The concentration of reactants and products at any point in an equilibeium reaction are related by what equation?

Answer 50

in equilibrium, ## Footnote **Q=K_c**

Question 51

If **Q\< K_c** what way does the reaction favour?

Answer 51

The reaction proceeds from left to right **favouring the products**

Question 52

If **Q\>K_c** what way does the reaction favour?

Answer 52

The reaction proceeds right to left **favouring the reactants**

Question 53

If there are more reactants than products, ∆G is negative, which way will the reaction shift and why?

Answer 53

The reaction will shift right in order to make ∆G=0 and therefore make the reaction in equilibrium

Question 54

if there are more products than reactants, the ∆G is positive, what way will the reaction shift and why?

Answer 54

The reaction will shift left in order to make ∆G=0 and the reaction to be in equilibrium

Question 55

What's **Van't Hoff isotherm** and whats the equation for it?

Answer 55

**∆G⁰= -RT ln(K)** **or after being rearranged to make K the subject:** **K= e^{(-∆G^0/RT})** This can beused to determine the Gibb's free energy for non-standard state reactions at a constant temperature. it can also help estimate the equilibrium shift It can be used to preduct K_c for ∆G⁰