L5/6 - thermodynamics Flashcards
why do we need to know about thermodynamics?
to know how drugs act on receptors, how drugs are distributed around body, how we formulate drugs into medicines
what is thermodynamics?
science of energy transfer
what is energy?
ability to perform work
what can thermodynamics tell you about a reaction?
whether a reaction or process will take place but NOT HOW FAST
what is kinetics?
study of rates or reactions or processes
what is kinetic energy?
the energy of movement of objects/ mass (mechanical energy)
what is potential energy?
energy that is stored (e.g nuclear energy)
what is heat?
form of energy caused by molecular motions. thermal energy is transferred between objects.
what is temperature?
- describes the tendency of heat to flow from one body to another
- initially sensory
freezing point of water
0 degrees celsius
boiling point of water
100 degrees celsius
body temperature
37 degrees celsius
what is the thermodynamic scale?
- used for accurate work
- zero on the scale = zero of molecular motion
- measured in kelvins (0 degrees celsius =0 in·kelvin² 273.15K)
what does work represent?
transfer of energy in an ordered fashion (remember heat is just random molecular motions)
what can work be defined as?
the energy barrier it overcomes
what are work and heat’s units?
joules (J)
W stands for?
work
Q stands for?
heat
total internal energy of system
U
isolated system
no matter or energy interaction or exchange with outside environment (completely sealed off) (e.g thermos flask)
closed system
no exchange of matter, can be exchange of energy (tight lid on cup of tea, can still lose energy but not the matter)
open system
both matter and energy can be exchanged with outside environment (hot cup of tea)
why do work and heat have an interdependence?
you can convert heat into work.
e.g if gas expands due to heat in piston, it will push piston up, performing work.
if you push piston back down, you are putting work against the system
so a system can do work, but can also have work performed on it.
what is internal energy the sum of?
the work which is done against the atmosphere + heat energy in system
if you put the piston in a high pressure environment?
to go to the same distance it would have to put in more work
work done on a system
+ W (positive number of joules)
work done by the system
- W (negative)
heat added to system
+ Q
heat rejected from system
- Q
first law of thermodynamics
energy cannot be created or destroyed, only transferred.
(algebraic sum of all energy changes in an isolated system is 0)
7 main forms of energy
- electrical
- gravitational
- chemical
- radiation
- thermal
- mechanical
- nuclear
electrical to mechanical
motors
gravitational to mechanical
falling weight
thermal to radiation
lightbulb
nuclear to thermal
atomic fission
concept of enthalpy
- physical and chemical reactions
- these are dominated by changes in heat energy
heat energy change within a change is expressed as?
enthalpy (H) - change
positive delta H
endothermic reaction as bonds are broken so energy is absorbed from the surroundings
negative delta H
exothermic reaction, bonds are created so energy is released to surroundings
what does the energy profile look like for a exo reaction?
reactants higher than products. arrow for -AH goes down. activation energy from reactants to peak
Crystallisation of a drug from the liquid to the solid state (HC) (where C stands for crystallisation)
exothermic
Melting of a drug (HF) (where F stands for fusion = melting)
endothermic
Evaporation of a volatile solvent (HV) (where V stands for vaporization)
endothermic
why is it wrong that reactions are driven by enthalpy?
many reactions take place spontaneously even though enthalpy change may not necessarily favour this taking place (e.g diffusion of gas in a vacuum)
entropy (S)
- related to disorder and probability
2nd law of thermodynamics
the entropy of an isolated system will either increase or stay the same but cannot decrease.
(disorder increases. if a reaction results in greater disorder then its more likely to happen)
the more disordered, the more…
the more disorder, the more entropy (so change S increases, becomes more positive)
if you chuck bricks in the air, why is it more probable for the bricks to fall in a very disordered way rather than stacked nicely?
more disordered states then there are ordered states
how is entropy associated with molecular motions (rotational & vibrational)?
greater the range of these motions (degrees of freedom), the greater the entropy.
what happens to reactions that result in a decrease in molecular motions?
not favoured due to the motions becoming more ordered
what do molecular motions increase with?
temperature
what is heat capacity?
amount of heat that needs to be supplied to an object to predict a unit change of its temperature
si units for heat capacity
joules per kelvin
what does heat capacity reflect?
ability to store heat energy
what can materials with higher range of molecular mobilities do?
store more energy
what do materials with high heat capacity have?
high entropy
high entropy =
more disordered
will entropy continue getting lower forever?
no, at some point you get to a state of perfect order
3rd law of thermodynamics?
at zero the entropy of a perfectly crystalline substance is 0. this is -273.15 degrees celsius where all molecular motion stops.
how to know if a reaction will occur spontaneously?
the balance between enthalpy and entropy (free energy (G))
Gibbs equation
G = H - TS
what is G
change in free energy
what actually is free energy?
- energy available to do work
what happens if there is negative free energy?
system can perform work on the surroundings and the reaction will be spontaneous
what happens if there is positive free energy?
system cannot perform work on its surroundings and the reaction will not be spontaneous
what is a spontaneous reaction favoured by?
- ve delta H (heat given out to surroundings, exothermic)
- +ve S entropy (system becomes more disordered)
how can a spontaneous reaction be endothermic (energy is absorbed)?
if the entropy is sufficiently positive
thermodynamics & the drug discovery process
- solubility of drug: max equilibrium concentration of drug in a given solvent
- melting point: transition from crystalline to liquid state (shows bond strength)
- partitioning: distribution of drug between oil and aq phases. (shows permeation across bio membrane)
drug receptor interactions
- drugs act via binding to specific receptors
- how binding works
- how binding can be manipulated
- thermodynamics shows bond strengths, free energy of interactions, molecular modelling, longevity of drug receptor interactions
A reaction taking place at room temperature has an enthalpy change of -561 kJ and an entropy change of +45 J/K. What is the free energy of the reaction?
ΔG = ΔH - TΔS
change in free energy = change in enthalpy - temp (K) x change in entropy
(-561kj) - (298 x 45/1000) = -574.41kJ/mol
Ice cream melts at around -10oC. However, on a hot day, the outside temperature is around 25-30oC. Why doesn’t ice cream liquify immediately?
it takes time for the heat to penetrate into the ice cream even though it equilibrium (thermodynamics) state is liquid at this temperature.
