Thermodynamics Flashcards
Whats the formula for the total internal energy of a system and what does each symbol stand for?
U = w + q
U= total energy of a system
w= work
q= heat
What are the forms of energy ?
- kinetic energy
- potential energy
Whats the formula for kinetic energy and what does each symbol represent?
Ekin= 1/2 MV2
m= mass
v= velocity
Whats are the two types of potential energy?
- gravitational potential energy
- chemical bond energy
What are the 3 types of system?
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
What is the first law of thermodynamics? what does this mean?
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
Whats the formula for work?
work = force x distance
According to Newton, what does force equal?
Force= mass x acceleration
Whats coulombs law and what do the symbols represent?
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
Whats the universal observation of energy transfer as heat?
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)
The energy changes derived from pressure and volume changes is given by what formula?
E = P x V
Whats the definition for the change in enthalpy?
∆H = ∆U + p∆V
Whats the definition for an endothermic reaction?
Any process which requires or absorbs energy from its surroundings, usually in the form of heat
∆H> 0 (positive)
what the definition of an exothermic reaction?
A chemical reaction that releases energy through light or heat
∆H < 0 (negative)
What are the standard conditions and what are they denoted by?
ø = 298 K and 1 atm/ 1 bar
How can enthalpy changes be measured in a closed system?
using a abomb calorimeter
What is the second law of thermodynamics?
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)
What is the definition of Entropy?
entropy,s, is defined as the number of microstates of a system
Whats the formula for entropy, using the boltzmann constant and microstates (being defined as omega)?
S= KB ln(omega)
Whats the change in entropy proportional to?
The change in entropy is proportional to the heat transferred from the system to the surroundings
Give the formula for entropy relationship with temperature and heat. What are the units?
∆S ≥ ∆q /T
∆q= joules, J
T= Kelvin, K
What does -∆S equal to with respects to heat and temperature?
-∆S = ∆Hsurroundings /T
What happens to entropy in the system and in the surroundings in an exothermic reaction?
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
∆Hsystem<0
What happens to entropy in the system and in the surroundings in an endothermic reaction?
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
∆Hsystem > 0
What are the conditions for a reaction to be able to occur spontaneously?
∆Stotal = ∆Ssystem + ∆Ssurroundings >0
for a reaction to occur spontaneously, the total entropy of the system and the surroundings need to increase
What is the equation for Gibbs free energy and the units of the components?
∆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
What are the quanities that describe a system and what do these represent?
Macrostates: temperature, pressure, volume
(things you can measure on whole system e.g. thermometer for temperature etc.)
Microstates: Kinetic energy, force, veolcity…
What can macrostates be descirbed as?
a collection of microstates
Whats the definition for equlibrium?
macrostates do not chnage over time (necessary condition for macrostates to be well-defined)
In isolated system in a thermal equilibrium, whats likely?
In an isolated system out of thermal equilibrium, how does it evolve?
In thermal equilibrium: all microstates are equally likely
Out of thermal equilibrium: It will evolve irreversable towards equilibrium
Whats the fomula describing the probability of any number of particles in a system?
P(N,NL) = N! / (N-NL)! x 1/2N
whats the hydrophobic effect?
The observed tendancy of nonpolar substances to aggregate in aq solution and exclude water molecules
What are the most common functions of the hydrophobic effect in biological systems?
- 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
Whats the basic structure of a phospholipid, what is it comprised of?
Why do mixed substances have more microstates?
They can be arranged in a greater number of ways
if ∆G>0, then is the solution more likely to mix or not to mix
The equilibrium is towards the demixed state. so mixing in the solution is less likely
if ∆H is close to 0, is this mixture likely to mix or not?
it is more likely to mix the closer to 0 it is
if T∆S is large and negative, is the mixture more likely to mix or not?
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
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?
6
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?
3
How does introducing hydrocarbons to water…
- explain phospholipid membrane assembly?
- explain the hydrophobic collapse in protein folding
- minimising the exposure of hydrocarbon chains to water, minimises the entropy of water in the presence of a phospholipid
- minmising the exposure of hydrocarbon containing sidechains to water maximises the entropy of water
What is the formula for Gibbs free energy?
∆G= ∆H - T∆S
whats the conditions for a spontaneous reaction, with reference to Gibbs free energy?
∆G< 0
How do you work out if ∆G<0?
What happens is ∆G is potive?
To calculate if ∆G<0…
∆G= Gproducts - Greactants
If the reaction is positive then it will occur in the opposite direction
What does the amount of ∆G transferred from the system to the surroundings determine?
The free energy that is available to do work
What does ∆G0 mean?
That its at a standard state and the value doesn’t change
whats does ∆G=0 mean?
that the reaction is in equilibrium
consider the reaction;
-aA + bB ⇔ cC +dD
Write the Kc equation for this and Kc general formula.
why is Kc written this way and what does it mean?
If you divide by the compounds in standard states then Kc becomes dimensionless (no units)
In Kc what type of number would you get in the following situations…
- if the products are smaller than the reactants
- If the products are bigger than the reactants
- If the products are an equal size to the reactants
1. Kc would be a small number
2. Kc would be a big number
3. some intermediate number
The concentration of reactants and products at any point in an equilibeium reaction are related by what equation?
in equilibrium,
Q=Kc
If Q< Kc what way does the reaction favour?
The reaction proceeds from left to right favouring the products
If Q>Kc what way does the reaction favour?
The reaction proceeds right to left favouring the reactants
If there are more reactants than products, ∆G is negative, which way will the reaction shift and why?
The reaction will shift right in order to make ∆G=0 and therefore make the reaction in equilibrium
if there are more products than reactants, the ∆G is positive, what way will the reaction shift and why?
The reaction will shift left in order to make ∆G=0 and the reaction to be in equilibrium
What’s Van’t Hoff isotherm and whats the equation for it?
∆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 Kc for ∆G0
