Biochemical Thermodynamics Flashcards
Definition of Thermodynamics:
Thermodynamics describes the relationship among various forms of energy and how energy effects matter on the
macroscopic level (e.g. temperature, entropy, pressure).
Importance of thermodynamic principles in biochemistry?
Thermodynamics is essential for understanding why
macromolecules fold into their native conformations, how metabolic pathways are designed, why molecules cross biological membranes, etc.
- Thermodynamics tells us which reactions will go forward and which ones won’t.
It is common observation that:
Some processes involving material substances
happen spontaneously, others do not.
Biochemistry studies the changes that occur to material
substances. The sorts of changes or processes that are of interest to biochemists include:
– Phase changes – e.g., melting, boiling, dissolving….
– Chemical reactions – substances change their
chemical nature (by changing the way in which their constituent atoms are bonded together to form
compounds)
– Physical processes – heating, cooling, expansion, compression, etc.
Thermodynamics will NOT tell us…
the rate at which possible processes occur
(that’s kinetics).
The original energy of the gas which
was localised and ordered becomes dissipated into a large number of random molecular motions. It is most unlikely that they will never get back into step.
In what way or ways can a chemical reaction increase the disorder of the system (the reacting substances) or its surroundings?
One way would be if the reaction emits heat (thermal
energy (i.e., if it is exothermic). The heat emitted by the reaction is dispersed in the form of thermal energy in the surroundings. This produces increased disorder and, as we have seen, this is a requirement for spontaneous
change.
entropy:
An increase in disorder
Given the symbol S.
Entropy acts as a measure of
the disorder associated with the atoms or molecules that make up a substance, and the dispersal of energy
associated with those particles.
Any substance, in a defined state…
(specified
values of T, p, etc.), has a specific entropy valueassociated with it.
The entropy of a substance is proportional to…
the number of ways in which the available energy can be distributed over the atoms or molecules of a system.
The entropy of substances..
increases with
increasing temperature.
Relationship between entropy and physical state:
So:
When solids —-> liquids Appreciable increase in S
When liquids —> vapours Very large increase in S
It turns out that there is a very fundamental
relationship between:
Spontaneity of
chemical
reactions and
other processes and entropy change
There exists a thermodynamic function
called…
entropy, denoted S, that has the
property that for any process the change in
entropy of the universe ΔS(univ) ≥ 0
