Key Takeaways
- Entropy (S) is a measure of disorder or randomness in a system
- For reversible processes at constant temperature: delta S = q/T
- Positive entropy change indicates increased disorder
- The Second Law states total entropy always increases in isolated systems
- Temperature must be in Kelvin (absolute temperature)
About the Entropy Change Calculator
This entropy change calculator helps you determine the change in entropy for thermodynamic processes. Entropy is a fundamental concept in thermodynamics that measures the degree of disorder or randomness in a system. Understanding entropy is crucial for predicting whether a process will occur spontaneously.
The Entropy Change Formula
delta S = q / T
This formula applies to reversible processes at constant temperature. For irreversible processes, the entropy change is greater than q/T.
Applications of Entropy Calculations
Entropy calculations are commonly used in:
- Chemical Reactions: Predicting spontaneity and equilibrium
- Phase Transitions: Calculating entropy of fusion and vaporization
- Engineering: Designing heat engines and refrigeration systems
- Materials Science: Understanding crystal structure and defects
- Biochemistry: Analyzing protein folding and enzyme catalysis
Understanding Entropy Signs
The sign of entropy change tells you about the direction of heat flow and disorder:
- Positive delta S: Heat absorbed (q > 0), system becomes more disordered
- Negative delta S: Heat released (q < 0), system becomes more ordered
- Zero delta S: Reversible adiabatic process (no heat exchange)
How to Use This Calculator
- Enter the heat transfer value (q) in Joules. Use positive values for heat absorbed and negative for heat released.
- Enter the temperature (T) in Kelvin. Remember: K = C + 273.15
- Click "Calculate" to see the entropy change
- Use "Reset" to clear all fields and start over
Frequently Asked Questions
Use Joules (J) for heat transfer and Kelvin (K) for temperature. The resulting entropy will be in Joules per Kelvin (J/K). For molar entropy, you may see units of J/(mol*K).
Kelvin is the absolute temperature scale where 0 K represents absolute zero - the lowest possible temperature. Using Celsius or Fahrenheit would give incorrect results because they can be negative, which would lead to incorrect entropy signs.
Gibbs free energy (G) combines entropy with enthalpy: delta G = delta H - T * delta S. A negative delta G indicates a spontaneous process. Entropy contributes to spontaneity, especially at high temperatures.
The entropy of a specific system can decrease (becoming more ordered), but the total entropy of the universe always increases for any real process. When a system's entropy decreases, the surroundings' entropy increases by an even greater amount.
For water: entropy of fusion is about 22 J/(mol*K) at 273 K, and entropy of vaporization is about 109 J/(mol*K) at 373 K. Vaporization has higher entropy change because gases are much more disordered than liquids.