PHSC1212 Biochemistry - Lecture 17 Cellular Bioenergetics and Carbohydrates

Enthalpy, entropy, free energy

three factors that control the directions of biochemical reactions

Enthalpy (H)

energy of a system (heat)

Heat or energy

What is enthalpy (H) a measure of?

Entropy (S)

degree of system disorder

Disorder

What is entropy (S) a measure of?

Free energy

amount of usable energy in a system that can be converted into work; will predict if a process will happen spontaneously

Usable energy

What is free energy a measure of?

Spontaneous or nonspontaneous

What characteristic of a reaction does free energy predict?

Spontaneous

physical or chemical changes that occur with the release of energy

First Law of Thermodynamics

states that the total amount of energy in the universe is constant; energy can neither be created nor destroyed, but it can be transformed from one form into another

Second Law of Thermodynamics

states that the disorder of the universe always increases; all chemical and physical processes occur spontaneously only when the disorder of the universe increases

Spontaneous process

What does it mean if S is positive for a process?

Third law of thermodynamics

states that as the temperature of a perfect crystalline solid approaches absolute zero (0 K), disorder approaches zero

Change in enthalpy

What is delta H?

Reaction gives off heat, exothermic

What does a negative delta H value mean?

Reaction absorbs heat, endothermic

What does a positive delta H value mean?

Isothermic

What does no change in delta H value mean?

Change in enthalpy minus temperature times change in entropy

equation for finding change in free energy

Kelvin

What should the temperature be in for the free energy equation?

Exergonic reaction, spontaneous

What does negative delta G value mean?

Endergonic reaction, nonspontaneous

What does positive delta G value mean?

Equilibrium

What does it mean if delta G is equal to zero?

25C or 298K, 1.0 atm pressure, 1.0 M solutes, pH 7.0

conditions for calculating change in free energy

Continuous consumption of products

What drives reversible reactions forward?

Adenosine triphosphate

the primary energy source for cellular functions (not abbreviated)

Open system

matter and energy exchanged between system and surroundings

Closed system

only energy can be exchanged