Brookes (L1-L9) Flashcards
What are the 3 types of chemical system?
Isolated: no exchange of energy or mass (material)
Open: exchange of energy (heat, work) and material
Closed: exchange of energy only not material
What is the difference between thermodynamics and kinetics and is represented by what part on an energy diagram
Thermodynamics: energy exchanges involved between different systems, relates to the enthalpy change between reactants and products
Kinetics: how quickly a reaction occurs, related to the activation energy in a reaction profile
What are the 4 types of closed systems?
Isobaric: constant pressure
Isothermal: constant temperature
Isochoric: constant volume
Adiabatic: no heat flow between system and surroundings (but can still have work done to)
What are the equations and definitions of internal energy?
Total energy of a system
Change in U = Ufinal - Uinitial
Change in U = q + w
What are the 3 assumptions of kinetic theory of gases?
- A gas consists of molecules of mass m and diameter d which are in constant random motion
- Size of molecules is negligible compared to the distances they travel
- No interactions between molecules except for perfectly elastic collisions (no energy loss)
Define temperature and heat
temperature: the average kinetic energy of particles/molecules in a material
heat: the flow of energy between objects of different average kinetic energy (temperature)
define work and its equation
A force in a particular direction
w = f x d
w = - P x change in V
What is a reversible process?
Direction of a reversible process can change by making an infinitesimal change to a variable/conditions (small differences)
What is the difference between a state function and path function? + examples
State function: only depends on a systems energetic state, what a system has (eg. U, temp, pressure)
Path function: amount of energy intrinsically associated with a process, what a system can do (eg. work, heat)
What is enthalpy change + its equation?
A measurement of heat changes to the system (can result in temperature change)
H = U + PV
(Or the energy within a system + the energy needed to create space for the system to exist)
what is PV in the enthalpy (H) equation?
The amount of work done to create space for the system to exist within the atmosphere (pressure x volume)
What are the standard state conditions of a material?
25 degrees (298.15K), 1 bar/ 1 atm / 1 x 10^5 Pa
What is the standard state?
The stable form of a substance under standard conditions
What is the definition of heat capacity and what is the equation for it?
Relating the temperature change of the whole system when a certain amount of heat is delivered to it (can be constant pressure or volume)
Units: J K^-1
C = change in heat / change in temperature
Define specific heat capacity and units
The amount of energy needed to raise 1kg of a material by 1 K
J kg^-1 K ^-1
Define molar heat capacity and units and equation
Heat energy to raise 1 mole of a substance by 1K
Units: J mol^-1 K^-1
total heat capacity = no. of moles x molar heat capacity
What are the symbols for heat capacity, specific heat capacity and molar heat capacity?
Heat captivity: capital C
Specific heat capacity: Lower case c
Molar heat capacity: capcital C with m
How do you combine heat capacities?
C = moles or mass of A x heat capacity of A + moles or mass of B x heat capacity of B ….
Enthalpy of formation for enthalpy equation
H = products - reactants
Enthalpy of combustion equation for enthalpy change
H = reactants - products
What is included within internal energy?
Intermolecular interactions and intramolecular interactions (chemical bonding)
ion ion interaction equation
u (r) = (coulomb constant x charge 1 x charge 2) / distance between them (r)
where constant = 8.99 x 10^9 Nm2c-2
what is the significance of positive and negative energy valuesin terms of bonding
positive: repulsive energy (not energetically favoured)
negative: attractive energy (energetically favoured)
what is the dipole equation
dipole moment = charge (equal magnitude but opposite sign) x distance between charges
why is the dipole-dipole interactions for tumbling molecules temperature dependent?
As the temperature increases the molecules have more kinetic energy thus rotate faster. This would decrease the amount of time for correlating attractive forces thus weakening the overall interaction/attraction
what are the VdW interactions equation and what interactions are included?
u(r) = C / r^6
- dipole dipole (tumbling)
- dipole next to polarizable (dipole induced dipole)
- dispersion interactions
VdW are for interactions that follow a r^-6 dependence
What does the Lennard Jones potential account for?
attractive interactions (negative) due to VdW and repulsive interactions (positive) due to overlap of electron clouds when TOO close together
What does the local minima in the Lennard-Jones potential represent?
The preferred separation of a molecule in their natural/relaxed state
what is the difference between enthalpy and entropy?
enthalpy comes from the interaction between molecules while entropy comes from the arrangement (while ignoring interactions)
what is an exothermic process and state the changes in energy under certain conditions
energy is released as heat, under constant pressure work cannot be done to the system thus heat energy is released (decreases both the enthalpy of a system and the internal energy of a system)
what is the difference between enthalpy and internal energy?
internal energy is a component of enthalpy (enthalpy also includes pressure and volume changes)
what is a spontaneous process?
a process that occurs without being driven (during the reaction) (eg. falling)
what must change or what can a spontaneous process be?
there must always be an increase in total entropy, however a spontaneous reaction can be both endothermic or exothermic
what are the 3 laws of thermodynamics/?
- energy cannot be created or destroyed, only transferred (the energy of an isolated system is constant)
- entropy of an isolated system tends to increase to a maximum for a spontaneous reaction
- the entropy of all perfect crystalline substances is zero at 0K
is entropy a state function or a path function?
state function (depends on the starting points and ending point not the path taken to get to it)
what are the phase changes from solid to liquid and liquid to gas called?
s -> l enthalpy/entropy of fusion
l -> g enthalpy/entropy of vaporization
what is the equation for entropy (number of ways to organize) and units for boltzmann
S = boltzmann x ln(number of ways to organise system)
boltzmann is in J K-1
what are the 2 ways to think about entropy?
level of disorder and number of ways components of a system can be arranged
describe thermal motion and ways of organizing a system at 0K
random thermal motion is removed, only 1 way of organizing system and ln1 = 0 (thus entropy is 0)
what is the equation for change in entropy?
entropy of products - entropy of reactants
how to calculate standard changes in entropy (or small changes in entropy)
dS = dqrev / T
what are the 3 equations for gibbs free energy?
dG = dH - tdS
dG = standard G + RTlnQ
dG = -RTlnK
*at equilibrium dG = 0 NOT standard G
what is the equation for counting arrangements if some of the molecules were the same?
total number of molecules ! / no. of indistinguishable molecules !
what is the equation for unique arrangements of multiplicity?
number of molecules! / all the categories of indistinguishable molecules !
N! / n1! x n2! … x nt!
define and give examples of between microstate and macrostate
macrostate is an observable state where we can make arrangements of properties (eg. volume and density of a gas in a container)
microstate is an individual snapshot of the specific organisation of the system (all microstates have the same density/volume/other properties)
collection of microstates = probability of seeing macrostate (average observable picture)
why is it more probable to see the gas fill up a container?
greater multiplicity with more space (more possible arrangements/microstates) thus greater probability of observing that specific macrostate
what is multiplicity?
the number of ways of organising the system in a particular state (the N value would be different)
do spontaneous reactions involve an increase or decrease in entropy?
increase
what is the difference between standard chemical potential and chemical potential of a substance?
standard the gibbs free energy of 1 mole of a substance at a concentration of 1 mol per dm^3 under standard conditions
just chemical potential is any concentration but just 1 mole of a substance (lower chemical potential compared to standard is favoured)
what is chemical potential/molar gibbs free energy ?
the gibbs free energy of a single chemical substance
what is enthalpy on a macro and micro scale?
macro -> heat energy released
micro -> interactions between molecules (bonding)
what is the symbol for chemical potential
μ
what is the equation that related standard chemical potential to chemical potential of a substance?
cp = scp + RTln[A]
*temperature is in K
*everything else should be in joules
what is an assumption with chemical potential?
solution behaves ideally (limited interactions between each other)
why is it more energetically favourable to move from a higher concentration to a lower concentration from a gibbs free energy perspective?
lower concentration means that there is more space for the molecules to explore (more ways to organise) thus energetically favoured thus the chemical potential is lower than the standard chemical potential
what is the equivalent equation for chemical potential but for gases?
change concentration into partial pressure (in bars)
how do you determine the total gibbs free energy of a mixture?
add up the chemical potential of the individual components (no. of moles x chemical potential)
G = sum of (n x μ)
how does changing the concentration affect the total gibbs free energy?
changes the concentration so chemical potential changes, changes the number of moles of the substance as well
what is the alternate way of looking at chemical potential?
rate of change of gibbs free energy over the number of moles of substance (increase in no. of moles means that the chemical potential is lower because u dont want to make more of it -> lower entropy)
what is an alternate equation for chemical potential (involving gibbs free energy)
cp = (dG / dni)
what is the gibbs free energy at equilibrium?
A minimum (delta G = 0)
what is the significance of a negative chemical potential value?
that a substance or species is thermodynamically favored to undergo a particular process or transformation
why do equilibrium reactions exist?
from an entropic perspective, it is more favourable (more arrangements) to have different components in a mixture rather than just products or just reactants
what is the reaction quotient for all products and all reactants?
all reactants = 0
all products = infinity
how can you determine the enthalpy and entropy of a reaction from a equilibrium constant and 1/T graph? + any assumptions
how is the graph derived?
gradient is - dH /R and the y intercept is dS/R
this assumes and S and H do not vary much with temperature
dH - TdS = -RTlnK
what is the difference between delta g and standard gibbs free energy
delta g: slope/tangent along the graph
standard: the total gibbs free energy change going from all reactants to all products
what are the 3 types of gibbs free energy and what do they represent?
G: total free energy of a mixture at any points in the reaction coordinate
dG: free energy change from reactants to products at any point in the reaction (dependent on concentration and conditions)
standard dG: free energy change going from 1 mole of reactants to 1 mole of products under standard conditions
how does the gibbs free energy value relate to the equilibrium constant value?
g = negative
lnk = positive
k > 1
preference towards the products (favours forward)
g = positive
lnk = negative
k < 1
preference towards the reactants
(favours reverse)
what is the relationship between equilibrium constant and rate constants for an equilibrium reaction?
K = rate of forward constant / rate of reverse constant
how are the rate constants related to the position of equilibrium?
the difference between the 2 rates determines the extent to which the reaction occurs thus relates the position of the equilibrium
what is the standard gibbs free energy equation
total products moles x chemical potential - total reactants moles x chemical potential
what the is chemical potential of any element in the standard state?
0
what equation shows the relationship between gibbs free energy and changes in temperature and pressure?
dG = VdP -SdT
how does entropy and volume relate to rate of gibbs free energy changes and explain the realtionship
higher entropy means that the system has more ways of arranging itself thus has greater rate of change of free energy with temperature
higher volume means more space for molecules to explore thus rate of change of gibbs free energy with pressure also increases
what is the typical entropy and enthalpy of a solid?
low entropy high enthalpy (bonding and interactions win)
what is a phase boundary?
occurs when 2 different physical states are in equilibrium with each other (free energy is the same)
what is the symbol for path function?
d with a line on top
how to you calculate a change in work done for a reversible process?
change in work done = - integra of PdV from V2 to V1
what is the equation for changes in H
dH = dU + PdV
what is the enthalpy change for reactions in solution and why?
change in H = change in U (internal energy)
the VP part disappears because pressure normally stays constant and unless a gas is produced the volume change is close to 0 thus both terms are cancelled out
what is the enthalpy change at constant pressure and constant volume?
constant pressure
change in H = heat
this means that changes in heat (q) directly relate to the change in energy of a system (positive q means that the reaction is taking in heat from the surroundings -> positive H and endothermic)
check lecture 4 for explanation
what is the equation for change in H for a gas?
change in H = change in internal energy + change in moles of gas x gas constant x temperature
*check L4 for explanation
under what condition can work can/cannot be done on a system?
can: constant pressure
cannot: constant volume
due to the work = - pressure x change in volume equation
what is the magic angle/best angle between 2 dipoles
50 degrees
what is the symbol for average interaction over all molecules?
<u(r)>
in the dispersion interactions equation, what do I and alpha represent?
I = ionization energy of molecule
alpha = polarizability of molecule
what is the lennard jones potential equation?
u(r) = 4e( (sigma /r)^12 - (sigma/r)^6 )
sigma is distance where interaction is 0
e is interaction strength
what is the entropy way of looking why gases expand/molecules mix in containers?
because the more space the system has the more ways to organise the system (more microstates) thus multiplicity (no. of microstates) is maximised which is favoured
mixing also maximises entropy so the process is spontaneous
define rate constant
number of successful collisions per unit time
what are the 2 equations for standard gibbs free energy change?
sG = sG of products - sG of reactants
sG = n x sμ (products) - n x sμ (reactants)
sμ = standard chemical potential
what is the clausius clapeyron equation?
ln (P1/P2) = Hvap / R x (1/T2 - 1/T1)
