Thermodynamics and Thermochemistry Quiz

Thermodynamics

• Thermodynamics is the study of relationships between heat, work, energy, and matter.
• It's crucial for understanding how energy transforms and matter behaves macroscopically.

First Law of Thermodynamics

• Energy cannot be created or destroyed, only transferred or converted.
• Expressed as ∆U = Q - W, where ∆U is internal energy change, Q is heat, and W is work.
• This law embodies the principle of energy conservation.

Thermochemistry

• Deals with heat changes during chemical reactions.
• Enthalpy (ΔH) is central, representing heat exchanged at constant pressure.
• Thermochemical equations calculate ΔH, aiding in understanding reaction energetics.
• These equations include the energy absorbed or released during a reaction.

Examples of Thermochemical Equations

• Combustion of methane: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l) ΔH = -890.3 kJ
• Formation of water: H₂(g) + ½O₂(g) → H₂O(l) ΔH = -285.8 kJ
• Melting of ice: H₂O(s) → H₂O(l) ΔH = +6.00 kJ
• Positive ΔH = Endothermic reaction
• Negative ΔH = Exothermic reaction

Second Law of Thermodynamics

• Illustrated by perfume diffusion: perfume molecules spontaneously spread throughout a room.
• Also illustrated by melting ice: initially ordered ice and water molecules become mixed.
• These processes increase entropy (disorder).

Third Law of Thermodynamics

• Entropy of a system approaches a constant value as temperature approaches absolute zero.
• Absolute zero is the point where molecular motion ceases.
• At absolute zero, entropy approaches a minimum value (typically zero)
• Entropy measures disorder or randomness in a system.

Third Law Applications

• Superconductivity: certain materials exhibit zero electrical resistance at very low temperatures (e.g., MRI machines, efficient power transmission).

Gibbs Free Energy

• Gibbs free energy (G) and Helmholtz free energy (A) describe a system's ability to do work at constant temperature and pressure.
• ΔG = ΔH - TΔS, where ΔG is change in Gibbs free energy, ΔH is enthalpy change, T is temperature in Kelvin, and ΔS is entropy change.
• ΔG<0 means spontaneous reaction
• ΔG>0 means non-spontaneous reaction

Test your knowledge on thermodynamics, focusing on the principles of energy transfer, the First Law of Thermodynamics, and thermochemical reactions. This quiz covers key concepts, including enthalpy and examples of thermochemical equations that demonstrate energy changes in reactions.