Entropy Flashcards
What does entropy tell?
How much disorder there is
What is entropy and give its symbol
• 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
What is the effect of more disordered particles
• More disordered particles means there is a higher entropy
• A large positive value of entropy shows a high level of disorder
How do physical states affects entropy and describe how
• 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
How does the number of particles affect entropy
• 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
How does more arrangements affect entropy
• 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
What does feasible mean?
• They just happen by themselves without the addition of energy
• Feasible reactions are sometimes spontaneous
Give the formula for entropy change
🔼H= S products - S reactants
What are the units of entropy change
JK-1 mol-1
Define entropy of a substance
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)
How can you find the standard entropy of products and reactants
• S products : add up the standard entropy of all the products
• S reactants: add up the standard entropy of all the reactants
Give the charge for entropy increase and decrease
• -284.4 J K-1 mol-1: entropy decrease
• 124.8 J K-1 mol-1: entropy increase
How will entropy be calculated when the reaction contains more than one mole of a reactant or product
• You’ll need to multiply the entropy value for that substance by the same number
Note
An increase in total entropy means that it is feasible for a reaction to occur but it’s not a guarantee that it will
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)
• 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
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
Check physical flashcards for answers
What other factors determine wether a reaction happens or not
• Enthalpy
• Temperature
• Kinetics
What are the units for temperature when calculating entropy?
- Kelvin, +273, -273
What are the units for enthalpy of solution
JK-1 mol-1
Write an equation, including state symbols, for the process that occurs when
potassium nitrate dissolves in water.
KNO3(s) → K+(aq) + NO3–(aq)
Suggest why the entropy change for this process is positive.
increase in disorder because solid → solution / increase in
number of particles / 1 mol (solid) gives 2 mol (ions/particles) /
particles are more mobile
