Entropy

Question 1

What does entropy tell?

Answer 1

How much disorder there is

Question 2

What is entropy and give its symbol

Answer 2

• Measure of the number of ways that particles can be arranged and the number of ways that the energy can be shared out between the particles
• S symbol

Question 3

What is the effect of more disordered particles

Answer 3

• More disordered particles means there is a higher entropy
• A large positive value of entropy shows a high level of disorder

Question 4

How do physical states affects entropy and describe how

Answer 4

• Solid particles just wobble about a fixed point- there’s hardly any disorder so they have the lowest entropy
• Gas particles whizz around. They have got the most disordered arrangements of particles so they have the highest entropy
• Physical states affect entropy

Question 5

How does the number of particles affect entropy

Answer 5

• More particles means more entropy
• The more particles you’ve got, the more ways they and their energy can be arranged
• Entropy increases because the number of moles increases

Question 6

How does more arrangements affect entropy

Answer 6

• More arrangements means more stability
• Substances always tend towards disorder
• They are more energetically stable when there’s more disorder
• Particles will have to increase their entropy
• This why some reactions are feasible even when the enthalpy change is endothermic

Question 7

What does feasible mean?

Answer 7

• They just happen by themselves without the addition of energy
• Feasible reactions are sometimes spontaneous

Question 8

Give the formula for entropy change

Answer 8

🔼H= S products - S reactants

Question 9

What are the units of entropy change

Answer 9

JK-1 mol-1

Question 10

Define entropy of a substance

Answer 10

The standard entropy of a substance is the entropy of 1 mole of that substance under standard conditions (at a pressure of 100kPa and a temperature of 298K)

Question 11

How can you find the standard entropy of products and reactants

Answer 11

• S products : add up the standard entropy of all the products

• S reactants: add up the standard entropy of all the reactants

Question 12

Give the charge for entropy increase and decrease

Answer 12

• -284.4 J K-1 mol-1: entropy decrease

• 124.8 J K-1 mol-1: entropy increase

Question 13

How will entropy be calculated when the reaction contains more than one mole of a reactant or product

Answer 13

• You’ll need to multiply the entropy value for that substance by the same number

Question 14

Note

Answer 14

An increase in total entropy means that it is feasible for a reaction to occur but it’s not a guarantee that it will

Question 15

Zinc carbonate breaks down when heated to form zinc oxide and carbon dioxide

• Would you expect the entropy change for this reaction to be positive or negative? Explain your answer

(Write the equation)

Answer 15

• You would expect the entropy change to be positive, because there are more moles of products than moles of reactant
• And the reactant is a solid while one of the products is a gas

Question 16

Nitrogen gas reacts with hydrogen gas to form ammonia: 3H2(g) + N2(g) -> 2NH3(g)

• Use the data given below to calculate the entropy change associated with this reaction

• S[NH3(g)] = 192JK-1 mol-1, S[H2(g)] = 131 JK-1 mol-1, S[N2(g)] = 192 JK-1 mol-1

Answer 16

Check physical flashcards for answers

Question 17

What other factors determine wether a reaction happens or not

Answer 17

• Enthalpy
• Temperature
• Kinetics

Question 18

What are the units for temperature when calculating entropy?

Answer 18

• Kelvin, +273, -273

Question 19

What are the units for enthalpy of solution

Answer 19

JK-1 mol-1

Question 20

Write an equation, including state symbols, for the process that occurs when
potassium nitrate dissolves in water.

Answer 20

KNO3(s) → K+(aq) + NO3–(aq)

Question 21

Suggest why the entropy change for this process is positive.

Answer 21

increase in disorder because solid → solution / increase in
number of particles / 1 mol (solid) gives 2 mol (ions/particles) /
particles are more mobile