Unit 4- Entropy Flashcards
What is a spontaneous reaction?
A reaction that occurs without any external factors
What is the requirement to be spontaneous at all temperatures?
To be either highly exothermic and lead to a greater disorder
what is entropy?
The measure of order in a system
What are factors which affect entropy
- Physical state
- Complexity
- Arrangement
Why is there a greater entropy when there is more quanta?
greater number of arrangements for the quanta
How does diffusion represent entropy?
particles in a system likely to be spread out therefore an increased entropy due to more disorder
As temperature increases, what happens to entropy?
Increases
Why does entropy increase as temperature increase?
due to a change in the physical state of a molecule
How does an increased temperature affect entropy?
Changes a molecule from solid to liquid to gas
Why does the physical state affect entropy?
- Entropy is a measure of disorder.
- A solid has the lowest entropy due to the greatest order e.g. lack of vibration
- A liquid has more disorder than a solid due to more free movement e.g. vibration and rotation
- A gas has the greatest disorder as the particles can freely move thus have the most arrangements in a system
How does complexity affect entropy?
An increased complexity increases entropy
Why does complexity affect entropy?
The more complex a molecule, the more atoms present. Therefore there are more possible arrangements of the particles thus more disorder
What has a larger entropy, a large molecule or lots of small molecules, and why?
Lots of small molecules as there are more possible arrangements in comparison to a large molecule
Explain the reaction where a solid is dissolved and give an example
- Increased entropy due to level of disorder increasing due to free movement in solution in comparison to a fixed position in a solid
- Ammonium nitrate is dissolved in water
- Temperature decreases therefore an endothermic reaction
- NH4NO3 + aq –> NH4+ + NO3-
Explain the reaction where a gas is produced and give an example
- Increased entropy due to a gas being produced
- Gas has the greatest entropy
- Ethanoic acid reacting with ammonium carbonate producing carbon dioxide as a product
- (NH4)2(s) + 2CH3COOH(aq) –> 2CH3COO-(aq) + 2NH4+(aq) + CO2<span>(g)</span>+ H2O(l)
Explain the reaction where a solid is produced through an exothermic reaction
- Entropy decreases due to a gas forming a solid therefore disorder decreases
- Burning magnesium in air
- 2Mg(s) + O2(g) –> 2MgO(s)
Explain the reaction where two solids react through an endothermic reaction?
- Dependent on the products formed in comparison to the product
- e.g. when barium hydroxide reacts with ammonia chloride
- 2NH4Cl(s) + Ba(OH)2.8H2O(s) +BaCl2.2H2O(s) + 2NH3(g) + 8H2O(l)
How to calulcate the entropy of a system?
Ssystem= Sproducts - Sreactants
How to calulcate the entropy of surroundings?
Ssurroundings = -H/T
How to calculate the total entropy?
Stotal = Ssystem + Ssurroundings
How does a feasible reaction occur?
when the total entropy is positive
What affects feasibilty in terms of Ssystem and H?
- Ssys is postive + H is positive - spontaneous at high temperatures
- Ssys is positive + H is negative- always spontaneous
- Ssys is negative + H is positive- never spontaneous
- Ssys is negative + H is negative- spontaneous at low temperatures
Define enthalpy of hydration of an ion?
Amount of energy released when one mole of the gaseous ions dissolve in water under standard conditions to produce a solution of 1moldm-3
e.g. M2+(s) + aq –> M2+(aq)
Define lattice energy
Amount of energy needed to break up an ionic crystal into seperate ions
