13.3.2 Calculating Entropy Changes

• $S$ is a measure of the disorder or randomness of a system.disorder
• The relationship between entropy and microstates is described by Boltzmann's equation.
• What is the value of Boltzmann's constant in SI units?

  1.38 \times 10^{ - 23} \text{ J / K}</latex>
• To calculate the change in entropy ($\Delta S$), we use the equation $\Delta S =$$S_{final} - S_{initial}$.final
• Higher entropy indicates more disorder in a system.
• Calculating entropy change involves using standard entropy values ($S^\circ$) for reactants and products
• Steps to calculate entropy change ($\Delta S^\circ$)


  1️⃣ Identify products and reactants

  2️⃣ Find standard entropy values

  3️⃣ Multiply by stoichiometric coefficients

  4️⃣ Sum products and reactants

  5️⃣ Calculate the difference
• What is the standard entropy change for the reaction $2H_{2}(g) +$$O_{2}(g) \rightarrow 2H_{2}O(l)$?


  - 326.8 \text{ J / mol·K}
• Entropy quantifies the number of possible microstates a system can exist in at a given temperature.
• The relationship between entropy and microstates is given by Boltzmann's equation: $S =$$k \ln W$.Boltzmann
• What does a higher entropy value indicate about a system?

  More disorder
• The Boltzmann's equation for entropy is $S =$$k \ln W$, where $W$ represents the number of microstates.
• What is the equation used to calculate standard entropy change ($\Delta S^\circ$)?


  $\Delta S^\circ =$$\Sigma S^\circ_{products} - \Sigma S^\circ_{reactants}$
• Steps to calculate standard entropy change ($\Delta S^\circ$)


  1️⃣ Identify products and reactants

  2️⃣ Find standard entropy values

  3️⃣ Multiply by stoichiometric coefficients

  4️⃣ Sum products and reactants

  5️⃣ Calculate the difference
• Calculate the standard entropy change for the reaction $2H_{2}(g) +$$O_{2}(g) \rightarrow 2H_{2}O(l)$ using standard entropy values.


  - 326.8 \text{ J / mol·K}
• Standard entropy values are found in standard entropy tables.
• The equation to calculate standard entropy change is $\Delta S^\circ =$$\Sigma S^\circ_{products} - \Sigma S^\circ_{reactants}$.
• What is the standard entropy change for the reaction $2CO(g) +$$O_{2}(g) \rightarrow 2CO_{2}(g)$?


  - 173 \text{ J / mol·K}
• Standard entropy values are used to calculate standard entropy change
• The equation for calculating standard entropy change is $\Delta S^\circ =$$\Sigma S^\circ_{products} - \Sigma S^\circ_{reactants}$
• Steps to calculate $\Delta S^\circ$


  1️⃣ Identify Products and Reactants

  2️⃣ Find Standard Entropy Values

  3️⃣ Multiply by Coefficients

  4️⃣ Calculate the Difference
• To find standard entropy values, you need to look them up in a standard entropy table
• For the reaction 2CO(g) + O_{2}(g) \rightarrow 2CO_{2}(g)</latex>, what is the standard entropy change ($\Delta S^\circ$) in J / mol·K?


  -173
• Match the term with its meaning:

  $\Delta S^\circ$ ↔️ Standard entropy change

  $S^\circ$ ↔️ Standard entropy value

  $\Sigma S^\circ_{reactants}$ ↔️ Sum of reactant entropies

  $\Sigma S^\circ_{products}$ ↔️ Sum of product entropies
• Steps to calculate \Delta S^\circ</latex>

  1️⃣ Identify Reactants and Products

  2️⃣ Find Standard Entropy Values

  3️⃣ Multiply by Coefficients

  4️⃣ Sum Reactant and Product Entropies

  5️⃣ Calculate the Difference
• For the reaction $2H_{2}(g) +$$O_{2}(g) \rightarrow 2H_{2}O(l)$, what is the standard entropy change ($\Delta S^\circ$) in J / mol·K?


  -326.8
• Entropy is related to the number of microstates by Boltzmann's equation $S =$$k \ln W$
• In Boltzmann's equation, $k$ is known as Boltzmann's constant
• What does entropy measure in a system?

  Disorder or randomness
• Entropy change for a reaction is calculated by subtracting the reactant entropies from the product entropies.
• For the reaction $2CO(g) +$$O_{2}(g) \rightarrow 2CO_{2}(g)$, what is the standard entropy change ($\Delta S^\circ$) in J / mol·K?


  -173
• The stoichiometric coefficient in a chemical reaction is used to multiply the entropy value.
• When calculating \Delta S^\circ</latex>, the entropy values of reactants are added together separately from products.
• What equation is used to calculate $\Delta S^\circ$?


  $\Delta S^\circ =$$\Sigma S^\circ_{products} - \Sigma S^\circ_{reactants}$
• Balancing the chemical equation is the first step in calculating $\Delta S^\circ$.
• The standard entropy values must be in units of J / mol·K.
• To calculate $\Delta S^\circ$, the entropy of reactants is subtracted from the entropy of products.
• Steps involved in applying standard entropy values in calculations

  1️⃣ Identify Products and Reactants

  2️⃣ Find Standard Entropy Values ($S^\circ$)

  3️⃣ Multiply by Coefficients

  4️⃣ Calculate the Difference
• What equation is used to calculate the change in standard entropy values ($\Delta S^\circ$)?


  $\Delta S^\circ =$$\Sigma S^\circ_{products} - \Sigma S^\circ_{reactants}$
• To find standard entropy values, you should look them up in standard tables