Lecture 5 and 6 - Thermodynamics Flashcards
What is thermodynamics?
The science of energy transfer, where energy is the ability to perform work.
Difference between kinetic energy and thermodynamics
Thermodynamics tells you energetically what will happen. It tells you whether a reaction or process will take place but not how fast- that is kinetics. Kinetics is energy associated with motion.
What is heat
Heat energy is caused by molecular motion. Heat is also considered in terms of thermal energy transfer between objects. E.g.. if you put your hand in hot water. the heat from water is being transferred to your hand. You are describing the thermal energy transfer between hot water and your hand.
three forms of heat
conduction, convection and radiation.
What is temperature?
Describes the propensity for heat to flow from one body to another.
History of measuring temperature- Newton.
- Newton developed scale from 0-12. Between water freezing and body temperature.
History of measuring temperature- Fahrenheit
Fahrenheit came along after newton and used freezing of a salt solution and body temperature with 96 divisions between the two. He added salt as an impurity to lower the base temperature. The Fahrenheit scale: 32 degrees being melting point of ice, 98.6 is body temperature and 212 is the boiling point of water.
History of temperature- Celsius
Celsius assigned freezing point of water as 0 degrees and boiling point as 100 degrees. Body temperature is 37 degrees.
How do you go from Fahrenheit to Celsius?
multiply by 1.8 and + 32
Thermodynamic temperature scale
Absolute zero= the zero of molecular motion. Measured in kelvins. 0 degrees Celsius is 273K.
What is work?
Heat refers to random molecular motions. Work represents the transfer of energy in an ordered fashion. Work is a form of energy expressed in joules, like heat.
The total energy of a system (U) is a combination of…
- heat energy Q
- Work W
Name the three types of systems
isolated, closed, open.
Isolated
completely closed off in terms of matter and energy.
Closed
closed off to transfer of matter, open to energy transfer.
Open systems
Completely open to the transfer of matter and energy.
Systems can work in two ways….
- can do work
- work can be done to it.
+W
work done on the system, positive joules
-W
work done by the system, negative joules
+Q
Heat added to the system
-Q
Heat rejected from the system
1st law of thermal dynamics
Energy cannot be created or destroyed, only transferred. Example= electrical to mechanical (motors)
Enthalpy change
The change/transfer in heat energy within a system during a reaction.
Endothermic reactions
- bonds are broken
- energy is absorbed from the surrounding
- positive energy change
Is crystallisation of a drug from liquid to solid state/ enthalpy change of crystallisation endo or exo?
exo because bonds are formed.
Exothermic reactions
- negative energy change
- bonds made
- energy lost to the surroundings.
Enthalpy change of fusion. Melting of a drug. Exo or Endo
Endothermic.
The 2nd law of thermodynamics refers to disorder. It states….
The entropy of an isolated system will either increase or stay the same but will not decrease. In other words, disorder tends to increase.
What does high Entropy (s) tell you about disorder and whether a reaction is likely to happen
- high entropy = more disorder = reaction is more likely to happen.
But why does disorder/entropy want to increase? Name too concepts to understand this.
Probability and molecular motion
Explain how probability links to entropy and disorder.
If a pack of cards are dropped, there are an infinite number of random piles that will form. The probability of the cards landing in a perfect pile is very small. Therefore, there are more possibilities for disorder to occur than for order to occur.
How does molecular motion explain disorder/entropy?
Entropy is associated with molecular motion that do not perform work (could be rotational or vibrational, for example). The greater the range of these motions/degree of freedom that these motions have, the greater the entropy. Reactions that result in a decrease of these motions are not favoured.
Motions are always present. When do they increase/ decrease?
Increase with increase in temperature. Decrease with a decrease in temperature.
What is heat capacity?
The amount of heat energy needed to be supplied to an object to produce a unit change in it’s temperature (j/k)
How does specific heat capacity differ to heat capacity?
Specific heat capacity is relevant to a specific mass of a substance. eg. the SHC of water is the heat energy needed to raise 1kg of water by 1degree Celsius.
Heat capacity reflects the ability to…
Store heat energy.
Tie together heat capacity, entropy and molecular mobilities.
Materials with a higher range of molecular mobilities can store more energy. We know heat capacity reflects the ability to store heat energy. Therefore, materials with a higher range of molecular mobilities have a higher heat capacity and also a higher entropy.
which has a higher specific heat capacity- water or copper?
water
Having a lower temperature= lower entropy. Can this process continue forever?
No. You reach a state where everything stops and is perfectly ordered.
What is the third law of thermodynamics?
- At absolute zero the entropy of a perfectly crystalline structure is zero.
Explain the 3rd law of thermodynamics.
- when you cool something down it has less kinetic energy. If something has zero kinetic energy it would be perfectly ordered- a crystalline structure. This zero kinetic energy happens at the absolute zero- temperature of 0K/-273 degrees C. At this point, entropy is zero.
To know if a reaction will take place spontaneously we use…
Free energy (G). The ability to perform work.
Give the Gibbs equation.
G = H - TS
Give the units for…
- free energy
- enthalpy change
- entropy change
- temp.
- Jmol^-1
- J
- JK^-1mol^-1
- K
If free energy change is negative…
then the system can perform work on the surroundings and the reaction will be spontaneous.
If free energy is positive then…
the system cannot perform work on it’s surroundings and the reaction will not be spontaneous.
For a spontaneous reaction to occur free energy must be negative. Therefore, enthalpy and entropy must be…
- enthalpy change= negative
- entropy change= positive
A spontaneous reaction could be endothermic if….
the entropy is positive enough.
Give three things that must be measured in a new drug that thermodynamics can help with
solubility, partitioning, melting point.
What is solubility?
the maximum equilibrium concentration of a drug in a given solvent. (maximum equilibrium concentration refers to the idea that if you add too much drug it won’t dissolve).
What is melting point? Why is knowing the melting point important?
the transition from the crystalline to the liquid state.
We need to know the melting point of a drug because it will indicate to us what the bond strengths are like in the drug.
What is partitioning?
Partitioning= the distribution of a drug between oil and aqueous phases. A ratio between how much drug dissolves in the oil and how much dissolves in the aqueous phase.
Why is partitioning of a drug important to know?
Drugs must dissolve in solution and then get through the lipid membrane of the gut (the gut epithelium). So the drug has to be able to dissolve AND get through the non-polar membrane. Basically, partitioning indicates how permeable a drug is across biological membranes.
What is an agnostic drug?
Binds to receptor site and enhances cellular activity.
What is an antagonistic drug?
Binds to the receptors and blocks cellular activity.
How can thermodynamics help us figure out the energy associated with a drug bonded to a receptor?
we could measure the heat energy associated with this reaction. As drug bonds to receptor heat will be released (endothermic)
What is another name for a surface active agent?
surfactant.
What is the structure of a surfactant?
have a hydrophobic and hydrophilic section.
How do they get their name?
surfactants absorb at surfaces so as to align with the hydrophobic and hydrophilic aspects of their environment.
The absorption process of surfactants happens spontaneously so free energy is…
negative
At a particular concentration, surfactants form micelles. What do we call this concentration>
critical micelle concentration.
Micelles are able to incorporate.
poorly water soluble drugs/ molecules.
People thought that the formation of micelles was entropically disallowed- more ordered so negative entropy. Why were they wrong?
The hydrophobic tails of the surfactants cause water molecules to align around the tails of surfactants to form a cage. Then , at the CMC, the micelles formed and the cage was broken up. this increased disorder- positive entropy- which compensated for the decrease in entropy when the micelles formed.
