Total Entropy Change (Universe) Calculator

Formula first

Overview

The Second Law of Thermodynamics states that the total entropy of an isolated system can only increase over time, or remain constant in ideal cases. This equation quantifies this fundamental principle by defining the total entropy change of the universe as the sum of the entropy change within a specific system and its immediate surroundings. A positive value for $\Delta$ $S_{universe}$ indicates a spontaneous process, driving towards greater disorder and energy dispersal.

Symbols

Variables

$\Delta$ $S_{system}$ = Entropy Change of System, $\Delta$ $S_{surroundings}$ = Entropy Change of Surroundings, $\Delta$ $S_{universe}$ = Total Entropy Change of Universe

Apply it well

When To Use

When to use: Use this equation to determine the spontaneity of a process. If \Delta S_{universe} is positive, the process is spontaneous. It's particularly useful in chemical thermodynamics to predict reaction feasibility and understand energy flow.

Why it matters: Understanding total entropy change is crucial for predicting the direction and feasibility of chemical reactions and physical processes. It underpins the concept of spontaneity and equilibrium, guiding the design of efficient chemical processes and understanding natural phenomena from biological systems to cosmological evolution.

Avoid these traps

Common Mistakes

• Forgetting to convert units (e.g., kJ to J).
• Incorrectly calculating $\Delta$ $S_{surroundings}$ or using the wrong sign.

One free problem

Practice Problem

A chemical reaction has an entropy change of the system ($\Delta$ $S_{system}$) of +45 J K⁻¹ mol⁻¹ and an entropy change of the surroundings ($\Delta$ $S_{surroundings}$) of -20 J K⁻¹ mol⁻¹. Calculate the total entropy change of the universe ($\Delta$ $S_{universe}$) for this reaction.

Solve for: Delta_S_universe

Hint: Remember to sum the two entropy changes.

The full worked solution stays in the interactive walkthrough.

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Related Formulas

References

Sources

1. Atkins' Physical Chemistry
2. Callen, Herbert B. Thermodynamics and an Introduction to Thermostatistics
3. Wikipedia: Second law of thermodynamics
4. IUPAC Gold Book: Entropy
5. Atkins' Physical Chemistry, 11th ed.
6. NIST CODATA
7. Atkins, P. W., & de Paula, J. (2014). Atkins' Physical Chemistry (10th ed.). Oxford University Press.
8. Callen, H. B. (1985). Thermodynamics and an Introduction to Thermostatistics (2nd ed.). John Wiley & Sons.