5.3.2 Entropy changes

• The second law of thermodynamics states that the entropy of an isolated system decreases over time.

  False
• Entropy is a measure of the disorder or randomness
• The main factors affecting entropy changes include temperature, pressure, and phase
• Entropy describes the number of possible arrangements
• Match the state with its entropy and molecular arrangement:

  Solid ↔️ Low entropy, tightly packed

  Liquid ↔️ Moderate entropy, loosely packed

  Gas ↔️ High entropy, widely dispersed
• The second law of thermodynamics states that the entropy of an isolated system not in equilibrium will approach a maximum
• Phase transitions from solid to gas increase entropy.


  True
• Match the state with its entropy:

  Solid ↔️ Low entropy

  Liquid ↔️ Moderate entropy

  Gas ↔️ High entropy
• Higher temperatures allow molecules to move more freely, increasing entropy
• Steps to calculate entropy change (ΔS°) using standard molar entropy values:

  1️⃣ Balance the chemical equation

  2️⃣ Find S° values for reactants and products

  3️⃣ Calculate total entropy of reactants

  4️⃣ Calculate total entropy of products

  5️⃣ Apply the formula ΔS° = (Products - Reactants)
• Consider the reaction: 2 H₂O(l) → 2 H₂(g) + O₂(g). The total entropy of the products is 467 J/K.
• A phase change from solid to gas increases entropy.


  True
• Why does increasing the number of gas molecules increase entropy?

  Gas molecules occupy more space
• The second law of thermodynamics states that the entropy of an isolated system increases over time.


  True
• What happens to entropy when heat dissipates from hot to cold areas?

  Increases
• To calculate entropy change, the formula used is ΔS° = (Total entropy of products) - (Total entropy of reactants).
• What is the balanced equation for the decomposition of water into hydrogen and oxygen gases?

  2 H₂O(l) → 2 H₂(g) + O₂(g)
• The formula to calculate the change in standard entropy is ΔS°
• What is the standard molar entropy (S°) value for H₂O(l)?

  70 J/mol·K
• Steps to calculate entropy change for a chemical reaction

  1️⃣ Balance the chemical equation

  2️⃣ Find S° values for reactants and products

  3️⃣ Calculate total entropy of reactants

  4️⃣ Calculate total entropy of products

  5️⃣ Apply the formula: ΔS° = (Products) - (Reactants)
• What is the standard molar entropy (S°) value for O₂(g)?

  205 J/mol·K
• Phase changes from solid to liquid to gas increase entropy.

  True
• Processes that increase entropy in a system

  1️⃣ Transition from solid to liquid

  2️⃣ Mixing different substances

  3️⃣ Increasing the number of gas molecules

  4️⃣ Forming more complex molecules
• A positive entropy change leads to a decrease in Gibbs free energy.


  True
• What is the relationship between entropy changes and Gibbs free energy?

  Entropy changes affect Gibbs free energy
• The entropy increases when a substance transitions from a solid to a liquid.

  True
• Entropy decreases when a substance transitions from a liquid to a gas.

  False
• Decreasing pressure typically increases entropy
• Entropy is a measure of the disorder or randomness
• Systems naturally move towards states of higher entropy because there are more possible arrangements of molecules in these states.


  True
• The change in entropy (ΔS°) for a reaction is calculated by subtracting the total entropy of products from the total entropy of reactants.

  False
• What is the formula for calculating the change in entropy (ΔS°)?

  $\Delta S^\circ =$$\sum S^\circ_{\text{products}} - \sum S^\circ_{\text{reactants}}$
• Steps to calculate the change in entropy for a reaction

  1️⃣ Balance the chemical equation

  2️⃣ Find S° values for reactants and products

  3️⃣ Calculate total entropy of reactants

  4️⃣ Calculate total entropy of products

  5️⃣ Apply the formula ΔS° = (Total entropy of products) - (Total entropy of reactants)
• Mixing substances typically increases entropy.
• What does entropy measure in a system?

  Disorder or randomness
• An isolated system does not exchange energy or matter with its surroundings.
• Processes that increase disorder in a system also increase entropy.

  True
• Steps to calculate entropy change using standard molar entropy values

  1️⃣ Balance the chemical equation

  2️⃣ Find S° values for reactants and products

  3️⃣ Calculate total entropy of reactants

  4️⃣ Calculate total entropy of products

  5️⃣ Apply the formula
• What is the first step in calculating the total entropy of reactants for a chemical reaction?

  Multiply S° by stoichiometric coefficient
• The reaction 2 H₂O(l) → 2 H₂(g) + O₂(g) is balanced.


  True