Lecture 1: Thermodynamics

Question 1

Thermodynamics

Answer 1

The relationship between energy, work, and heat.

Question 2

Energy

Answer 2

Capacity to do work

Question 3

Work

Answer 3

Transfer of energy from the system to surroundings that can raise a weight

Question 4

Heat

Answer 4

Transfer of energy as a result of a difference in temperature

Question 5

First law of thermodynamics

Answer 5

Any change in the internal energy (U) of a system must equal the transfer of energy as heat or work

Question 6

Enthalpy

Answer 6

The thermodynamic potential of a system. At constant pressure, enthalpy is equivalent to the amount of heat in the system.

Question 7

Spontaneous process

Answer 7

Has a tendency to occur without us or anyone else having a part in it.

Question 8

Spontaneous vs non-spontaneous process

Answer 8

Spontaneous: tends to occur without the input of energy (breaking an egg on the floor)
Non-spontaneous: requires input of energy to occur (reforming of the broken egg)

Question 9

Second law of thermodynamics

Answer 9

Entropy of a system tends to increase

Question 10

Entropy (S)

Answer 10

Number of energetically equivalent arrangements of the system (J K-1). Entropy is a function of temperature

Question 11

Change in entropy > 0

Answer 11

When a spontaneous process has no overall change in energy or entropy

Question 12

Driving forces of spontaneous processes

Answer 12

1. Negative change in enthalpy, meaning heat is transferred from the system to the surroundings
2. Increase in entropy from the initial state to the final state

Question 13

Gibbs free energy

Answer 13

The true indicator of spontaneity. Gibbs relates changes in entropy to enthalpy via temperature.

Question 14

Mechanical example of Gibbs free energy

Answer 14

We have a weight that can either go up a hill or down a hill. The free energy of the weight at the bottom of the hill is lower than the free energy at the top of the hill.
Positive change in free energy: required to move the weight from the bottom to the top of the hill (endergonic, non-spontaneous process).
Negative change in free energy: when the weight is moving from the top to the bottom of the hill (exergonic, spontaneous process).

Question 15

Chemical example of Gibbs free energy

Answer 15

If the free energy of the reactants is above the free energy of the products, free energy will be negative and the reaction will be spontaneous.

If the free energy of the reactants is lower than the free energy of the products, free energy will be positive and the reaction will be non-spontaneous.

ΔG ≤ 0 indicates an exergonic rxn.
ΔG > 0 indicates an endergonic rxn

Question 16

Negative enthalpy and positive entropy

Answer 16

Enthalpically favored and entropically favored. Spontaneous at all temperatures

Question 17

Negative enthalpy and negative entropy

Answer 17

Enthalpically favored and entropically unfavored. Spontaneous at temperatures below T = change in H/change in S

Question 18

Positive enthalpy and positive entropy

Answer 18

Enthalpically unfavored and entropically favored. Spontaneous at temperatures above T = change in H/change in S.

Question 19

Positive enthalpy and negative entropy

Answer 19

Enthalpically unfavored and entropically unfavored. Nonspontaneous at all temperatures

Question 20

Chemical coupling

Answer 20

In coupled biological reactions, the usual source of free energy comes from ATP. Chemical coupling allows otherwise unfavorable reactions. The high energy ATP molecule reacts directly with the metabolite that needs activation.

Question 21

Factors affecting free energy change

Answer 21

• Concentrations of reactants and products

- Standard conditions (25 C, 1 atm, pH 7)

Question 22

Reaction at equilibrium

Answer 22

The net change in free energy for a reaction at equilibrium is 0. At equilibrium, the free energy change of the forward reaction exactly balances that of the reverse reaction

Question 23

Equilibrium constant vs. temperature

Answer 23

The equilibrium constant is dependent on temperature.

Question 24

Van’t Hoff equation

Answer 24

Shows the relationship between free energy change and the equilibrium constant. It resembles y = mx +b.

Question 25

Plotting data using Van’t Hoff

Answer 25

Data can be plotted on a Van’t Hoff graph, where the y-axis is the natural log of the equilibrium constant and the x-axis is 1/T. The slope of the graph is equal to (-) the standard change in enthalpy over the gas constant R. The Y intercept is equal to the standard change in entropy over the gas constant R.