Thermodynamics and Energy Flashcards
Grade 10 · Science · Flashcards
Key thermodynamic concepts, laws, and formulas for understanding energy changes in chemical and physical processes.
Flashcards
- First Law of Thermodynamics
- Energy is conserved in the universe: ΔU = q + w (internal energy = heat + work)
- Second Law of Thermodynamics
- Entropy of the universe always increases in a spontaneous process; ΔS_universe > 0
- Third Law of Thermodynamics
- Entropy of a perfect crystal at 0 K equals zero; provides an absolute reference point for entropy
- Enthalpy (ΔH)
- Heat transferred at constant pressure; negative for exothermic, positive for endothermic reactions
- Entropy (ΔS)
- Measure of disorder/randomness; increases when going from solid→liquid→gas, or increasing complexity
- Gibbs Free Energy
- ΔG = ΔH - TΔS; predicts spontaneity: ΔG < 0 spontaneous, ΔG > 0 non-spontaneous, ΔG = 0 equilibrium
- Exothermic reaction
- ΔH < 0; system releases heat to surroundings; products more stable than reactants
- Endothermic reaction
- ΔH > 0; system absorbs heat from surroundings; products less stable than reactants
- Hess's Law
- ΔH_rxn = Σ ΔHf°(products) - Σ ΔHf°(reactants); enthalpy is a state function
- q = mcΔT
- Heat transfer formula: q = mass × specific heat × temperature change; T in °C or K
- Calorimetry
- Measuring heat flow in reactions using a calorimeter; q_rxn = -q_solution
- Activation energy (Ea)
- Minimum energy required for reactants to begin a chemical reaction; lowers with a catalyst
- Spontaneity table
- ΔH<0 ΔS>0 → always spontaneous; ΔH>0 ΔS<0 → never spontaneous; mixed signs → T-dependent
- Standard state
- Pure substance in most stable form at 25°C and 1 atm; standard enthalpy of formation of an element in standard state = 0
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