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Thermodynamics
Thermodynamics studies energy changes in chemical reactions. Learn enthalpy, entropy, Gibbs free energy, Hess's law, and predict whether reactions are spontaneous.
Key Concepts
Study Tips
- ✓Remember: negative delta H = exothermic, positive delta H = endothermic
- ✓Use Hess's Law by manipulating equations like algebra
- ✓Gibbs Free Energy: delta G = delta H - T(delta S)
- ✓A reaction is spontaneous when delta G is negative
Common Mistakes to Avoid
Common errors include forgetting to reverse the sign of delta H when reversing a reaction, not multiplying delta H when coefficients change, confusing system and surroundings, and forgetting temperature must be in Kelvin for Gibbs free energy calculations.
Thermodynamics FAQs
Common questions about thermodynamics
A reaction is spontaneous when delta G < 0. Use delta G = delta H - T(delta S). Exothermic reactions (negative delta H) with increased entropy (positive delta S) are always spontaneous. Other combinations depend on temperature.
Hess's Law states that the total enthalpy change for a reaction is the same regardless of the pathway taken. You can add, subtract, or multiply known reactions to find the enthalpy of an unknown reaction.
q = mc(delta T), where q is heat, m is mass, c is specific heat capacity, and delta T is temperature change. For reactions in solution, the heat released by the reaction equals the heat absorbed by the solution.