Chapter 2: Thermodynamics

Question 1

Define a System

Answer 1

Any part of the universe with defined boundaries. It can be limited to a pair of reacting molecules, a cell, an organism…

Question 2

Define Surroundings

Answer 2

The universe minus the system

Question 3

Define Energy

Answer 3

The capacity of a system to do work and/or to exchange heat

Question 4

What is the difference between an isolated, closed, and open system?

Answer 4

Isolated System: No Energy or Matter Exchanged

Closed System: Energy is Exchanged but not Matter

Open System: Both Energy and Matter are Exchanged

Question 5

Where is the energy of a molecule stored?

Answer 5

Within Covalent Bonds, Non-Covalent Interactions, and the molecule’s Levels of Freedom

Question 6

What does it mean that Energy is a “State Function”?

Answer 6

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

Question 7

What does “H” stand for? What does it mean when ▲H is greater than 0? Less than 0?

Answer 7

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

Question 8

What does Bond Energy refer to?

Answer 8

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!

Question 9

What is “Hf”?

Answer 9

Heat of Formation - The energy difference between a molecule and its individual un-bonded atoms

Question 10

What is Entropy and how is it denoted?

Answer 10

Entropy is the energy that is lost to increase the “randomness” of the universe. It is denoted by the letter “S”.

Question 11

What does it mean if ▲S > 0?

Answer 11

The process is often spontaneous, but not always

Question 12

As Entropy increases what happens to potential energy?

Answer 12

As Entropy increases, Potential Energy of the system decreases

Question 13

Who combined the terms Enthalpy (H) and Entropy (S)? What was the new term called?

Answer 13

J. Willard Gibbs combined Enthalpy and Entropy to define a new state function know as “Free Energy” denoted as G

Question 14

▲G = ▲H - T▲S

What do each of these symbols mean?

Answer 14

▲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)

Question 15

What are the ▲G’s of Exergonic and Endergonic Reactions?

Answer 15

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.

Question 16

What are the conditions for Standard Free Energy Change (▲G°)?

What about Biochemical Standard Free Energy Change (▲G°’)?

Answer 16

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).

Question 17

What does it mean if ▲G is 0?

Answer 17

It means that the system has reached a state of Equilibrium.

Question 18

Is Chemical Equilibrium favorable for biological systems? Why or why not?

Answer 18

Chemical Equilibrium is undesirable for biological systems because it leads to a state of thermodynamic death where no more work can be done.

Question 19

For the following reaction describe the forward and reverse rate:

A + B ⇆ C + D

Answer 19

Forward Rate: k(f) = [A][B]

Reverse Rate: k(r) = [C][D]

Question 20

What is the equilibrium constant?

Answer 20

k(eq) = [Products]/[Reactants]

Question 21

What is the equation to find Biochemical Standard Free Energy Change (▲G°’) from the Equilibrium Constant (K(eq))?

Answer 21

▲G°’= -RT ln K(eq)

R = 8.315 J/mol (This is the Gas Constant)

T = Absolute Temperature

Question 22

How would you find ▲G’ from ▲G°’?

Answer 22

▲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