🧤physical chemistry i review

key term - Entropy change

Definition

Entropy change refers to the measure of the disorder or randomness in a system and how it varies during a process. It is crucial for determining whether a process is spontaneous or non-spontaneous, as spontaneous processes generally result in an increase in entropy of the universe. Understanding entropy change also plays a significant role in thermodynamic cycles and helps to quantify the efficiency of heat engines.

5 Must Know Facts For Your Next Test

  1. Entropy change can be calculated using the formula $$\Delta S = \frac{Q_{rev}}{T}$$, where $$Q_{rev}$$ is the reversible heat transfer and $$T$$ is the temperature in Kelvin.
  2. In a closed system, the total entropy change is equal to the sum of the entropy changes of the system and its surroundings.
  3. For a reversible process, the total entropy change is zero, while irreversible processes always lead to an increase in total entropy.
  4. In heat engines, maximizing efficiency involves minimizing entropy changes, which allows for more work to be extracted from the heat input.
  5. Standard molar entropies are tabulated values that provide a reference point for calculating entropy changes in reactions at standard conditions.

Review Questions

  • How does entropy change determine if a process is spontaneous or not?
    • Entropy change is key in assessing spontaneity because spontaneous processes tend to increase the overall entropy of the universe. If the total entropy change, which includes both system and surroundings, is positive, it indicates that the process can occur without external input. This relationship is summarized by the Second Law of Thermodynamics, emphasizing that natural processes favor increasing disorder.
  • Discuss how the Carnot cycle illustrates principles related to entropy change and heat engines.
    • The Carnot cycle serves as an idealized model for heat engines that demonstrates maximum efficiency through reversible processes. During each phase of this cycle, changes in entropy are critical in understanding energy transfer between hot and cold reservoirs. The cycle reveals that while heat is absorbed and released, the total change in entropy for the entire system remains constant, aligning with the Second Law. This efficiency limit highlights how real engines must account for unavoidable increases in entropy due to irreversibilities.
  • Evaluate the significance of standard molar entropies in calculating entropy change for chemical reactions.
    • Standard molar entropies provide essential data for calculating overall entropy changes during chemical reactions under standard conditions. By using tabulated values, one can assess how disorder increases or decreases when reactants are converted into products. This evaluation not only helps predict spontaneity but also provides insight into reaction feasibility, allowing chemists to design reactions that maximize efficiency by understanding their thermodynamic landscape related to entropy changes.