Chapter 2: Thermodynamics Flashcards
Define a System
Any part of the universe with defined boundaries. It can be limited to a pair of reacting molecules, a cell, an organism…
Define Surroundings
The universe minus the system
Define Energy
The capacity of a system to do work and/or to exchange heat
What is the difference between an isolated, closed, and open system?
Isolated System: No Energy or Matter Exchanged
Closed System: Energy is Exchanged but not Matter
Open System: Both Energy and Matter are Exchanged
Where is the energy of a molecule stored?
Within Covalent Bonds, Non-Covalent Interactions, and the molecule’s Levels of Freedom
What does it mean that Energy is a “State Function”?
The path by which the system went from state 1 to 2 will have no effect on the net change in the system’s energy
What does “H” stand for? What does it mean when ▲H is greater than 0? Less than 0?
H stands for Enthalpy which is the heat content of the system
When ▲H > 0, the reaction releases heat and is exothermic
When ▲H < 0, the reaction takes up heat from the surroundings and is endothermic
What does Bond Energy refer to?
It is the energy exchanged between the system and surrounding when a chemical bond is formed or broken
Remember: Energy is released when a chemical bond is formed and energy is needed to break a bond!
What is “Hf”?
Heat of Formation - The energy difference between a molecule and its individual un-bonded atoms
What is Entropy and how is it denoted?
Entropy is the energy that is lost to increase the “randomness” of the universe. It is denoted by the letter “S”.
What does it mean if ▲S > 0?
The process is often spontaneous, but not always
As Entropy increases what happens to potential energy?
As Entropy increases, Potential Energy of the system decreases
Who combined the terms Enthalpy (H) and Entropy (S)? What was the new term called?
J. Willard Gibbs combined Enthalpy and Entropy to define a new state function know as “Free Energy” denoted as G
▲G = ▲H - T▲S
What do each of these symbols mean?
▲G = Change in Free Energy
▲H = Enthalpy Change of the Reaction
T = Absolute Temperature in Kelvin (= Temperature in Celcius + 273)
▲S = Entropy Factor (Change in Entropy)
What are the ▲G’s of Exergonic and Endergonic Reactions?
The ▲G for an Exergonic Reaction will always be less than 0 (Negative) and means that energy is released into the environment. This also means there is a net loss of potential energy.
▲G for an Endergonic Reaction will always be greater than 0 (Positive) and means energy is being absorbed from the environment. This means there is a net gain of potential energy.
What are the conditions for Standard Free Energy Change (▲G°)?
What about Biochemical Standard Free Energy Change (▲G°’)?
Standard Free Energy Change (▲G°):
- 1.0 molar starting concentration of each of the reactants and products
- At a temperature of 25°C (298°K)
- At 1.0 Atmosphere pressure
- Reaction is allowed to proceed to completion or to an equilibrium (no further change in the concentrations of reactants and products)
Biochemical Standard Free Energy Change (▲G°’)
- Same as ▲G° with the following changes:
- pH = 7.0
- Concentration of water omitted (even if it participates in the reaction).
What does it mean if ▲G is 0?
It means that the system has reached a state of Equilibrium.
Is Chemical Equilibrium favorable for biological systems? Why or why not?
Chemical Equilibrium is undesirable for biological systems because it leads to a state of thermodynamic death where no more work can be done.
For the following reaction describe the forward and reverse rate:
A + B ⇆ C + D
Forward Rate: k(f) = [A][B]
Reverse Rate: k(r) = [C][D]
What is the equilibrium constant?
k(eq) = [Products]/[Reactants]
What is the equation to find Biochemical Standard Free Energy Change (▲G°’) from the Equilibrium Constant (K(eq))?
▲G°’= -RT ln K(eq)
R = 8.315 J/mol (This is the Gas Constant)
T = Absolute Temperature
How would you find ▲G’ from ▲G°’?
▲G’ = ▲G°’ + RTln([Products]/[Reactants])
R = 8.315 J/mol
T = Absolute Temperature
Note: The concentrations are the actual concentrations and not the standard ones
