Entropy and Spontaneous Changes Flashcards
Spontaneous Change
- Continues to progress forward on its own once it has begun
Spontaneous Change Example
- Lighting a match
- Strike it once, flame continues until reactants are gone
Non-Spontaneous Change
- Cannot occur without a continual input of energy
Non-Spontaneous Change Example
- Boiling a pot of water
- Removing the heat stops the boiling
What can the concept of spontaneity help us determine?
- How likely it is for certain reactions to take place
- Important in biological systems where reactions need to be highly controlled
What factors of the table are favoured?
- Exothermic Changes
- Increase in Entropy
What factors of the table are not favoured?
- Endothermic Changes
- Decrease in Entropy
Exothermic Changes + Increase in Entropy
- Spontaneous at all temps
- Ex. Wood burning, food colouring dispersing in water, cell respiration
Exothermic Changes + Decrease in Entropy
- Rare
- Spontaneous at low temps
- Not spontaneous at high temps
- Ex. Water freezing
Endothermic Changes + Increase in Entropy
- Spontaneous at high temps
- Not spontaneous at low temps
- Ex. Sweat evaporating from skin, ice melting
Endothermic Changes + Decrease in entropy
- Not spontaneous at any temp
- Requires continuous input of energy to move forward
- Ex. Plants making glucose (photosynthesis), rolling a ball uphill
Who is Josiah Gibbs?
An American scientist that described “free energy” in 1873
What is Free Energy?
- Energy available to do useful work
What is Free Energy used for in living organisms
- Anabolism, reproduction and movement
- Needed to do chemical and physical work
Formulas to calculate the change in free energy (△G)
- △G=△H-T△S
- △G=G final state - G initial state
What does △S represent?
Change in entropy
What does T represent?
- Temperature
- In Kelvins
What does a negative △G indicate?
- Free energy of the products is less than that of the reactants
- A reaction will occur spontaneously
- Exergonic reactions
What do negative △G values do in biology?
- That energy can produce ATP which can be used to carry out cellular work
What does a positive △G indicate?
- Free energy of the products is more than that of the reactants
- Indicates a reaction must gain free energy from another source in order to occur
- These are non-spontaneous reactions
- Endergonic reactions
What do positive △G values do in biology?
These reactions consume ATP in order to move forward
Exergonic Reactions
- Reaction is spontaneous
- Energy is released
- △G<0
- Similar to exothermic reactions but graph is shifted down
Endergonic Reactions
- Reaction is not spontaneous (usually needs ATP)
- Energy is absorbed
- △G>0
- Similar to endothermic reactions but graph is shifted down
