Unit 4- Entropy

Question 1

What is a spontaneous reaction?

Answer 1

A reaction that occurs without any external factors

Question 2

What is the requirement to be spontaneous at all temperatures?

Answer 2

To be either highly exothermic and lead to a greater disorder

Question 3

what is entropy?

Answer 3

The measure of order in a system

Question 4

What are factors which affect entropy

Answer 4

• Physical state
• Complexity
• Arrangement

Question 5

Why is there a greater entropy when there is more quanta?

Answer 5

greater number of arrangements for the quanta

Question 6

How does diffusion represent entropy?

Answer 6

particles in a system likely to be spread out therefore an increased entropy due to more disorder

Question 7

As temperature increases, what happens to entropy?

Answer 7

Increases

Question 8

Why does entropy increase as temperature increase?

Answer 8

due to a change in the physical state of a molecule

Question 9

How does an increased temperature affect entropy?

Answer 9

Changes a molecule from solid to liquid to gas

Question 10

Why does the physical state affect entropy?

Answer 10

• 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

Question 11

How does complexity affect entropy?

Answer 11

An increased complexity increases entropy

Question 12

Why does complexity affect entropy?

Answer 12

The more complex a molecule, the more atoms present. Therefore there are more possible arrangements of the particles thus more disorder

Question 13

What has a larger entropy, a large molecule or lots of small molecules, and why?

Answer 13

Lots of small molecules as there are more possible arrangements in comparison to a large molecule

Question 14

Explain the reaction where a solid is dissolved and give an example

Answer 14

• 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^-

Question 15

Explain the reaction where a gas is produced and give an example

Answer 15

• 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) + CO_{2<span>(g)</span>}+ H₂O_(l)

Question 16

Explain the reaction where a solid is produced through an exothermic reaction

Answer 16

• Entropy decreases due to a gas forming a solid therefore disorder decreases
• Burning magnesium in air
• 2Mg_(s) + O_2(g) –> 2MgO_(s)

Question 17

Explain the reaction where two solids react through an endothermic reaction?

Answer 17

• 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) + 2NH_3(g) + 8H₂O_(l)

Question 18

How to calulcate the entropy of a system?

Answer 18

S_system= S_products - S_reactants

Question 19

How to calulcate the entropy of surroundings?

Answer 19

S_surroundings = -H/T

Question 20

How to calculate the total entropy?

Answer 20

S_total = S_system + S_surroundings

Question 21

How does a feasible reaction occur?

Answer 21

when the total entropy is positive

Question 22

What affects feasibilty in terms of S_system and H?

Answer 22

• S_sys is postive + H is positive - spontaneous at high temperatures
• S_sys is positive + H is negative- always spontaneous
• S_sys is negative + H is positive- never spontaneous
• S_sys is negative + H is negative- spontaneous at low temperatures

Question 23

Define enthalpy of hydration of an ion?

Answer 23

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)

Question 24

Define lattice energy

Answer 24

Amount of energy needed to break up an ionic crystal into seperate ions

Question 25

Define enthalphy of solution

Answer 25

The enthalpy change when 1 mole of the compound dissolves in a stated amount of water under standard conditions

Question 26

How to calculate the enthalpy of solution?

Answer 26

Difference between the energy needed to seperate the ions from the cyrstal lattice and the energy given out when the ions are hydrated

There H_sol = H_hyd - Lattice energy

Question 27

What affects lattice energy thus enthalpy of solution?

Answer 27

• An increase in ionic radii , decreases lattice energy
• Solids consisiting of divalent ins have higher lattice energies in comparison to monovalent ions

Question 28

When does an ionic compound dissolve?

Answer 28

when hydration energy is greater than the lattice energy