W3-Thermodynamics

Study Notes

Molecular energy: All chemical energy changes are related to potential and kinetic energies of molecules. Potential energy is 'stored energy' and transformed into kinetic energy.
1st law of thermodynamics: Energy cannot be created or destroyed, only transferred between systems and surroundings as work or heat.
Internal energy: A molecule's total energy consists of nuclear, inter/intramolecular forces, kinetic, and potential energies.
Classification of systems: Systems are classified based on their interaction with surroundings: isolated (no energy or mass transfer), closed (energy transfer only), and open (energy and mass transfer).
Heat: Heat is thermal energy, related to the motion of atoms and molecules. It is transferred between systems and surroundings via work or heat.
Calories: Heat is measured in calories (or gram-calories), with 1 calorie being the energy required to raise 1 gram of water by 1 degree Celsius.
Work: Work is energy transferred to move an object against a force. In a system, work is done by the system when it expands against a constant external pressure.
Energy changes in chemical systems: Chemical reactions, such as drug decomposition, can involve expansion work due to the production of gaseous products.
Minimum work: When a gas expands into an evacuated space at constant temperature, the work done on the gas is minimal because there is no external pressure opposing the expansion.
Interpreting Work: In each scenario, the energy of the system can be determined by evaluating whether the work done on or by the system results in a positive or negative change in internal energy.
Expansion work in chemical systems: Expansion work is the work done by a system when it expands against a constant external pressure. This work is equal to the negative product of pressure, volume, and temperature for an isothermal expansion.
Minimum work in gas expansion: The work done on a gas, like in the case of gas expanding into an evacuated space, is minimal because there is no external pressure opposing the expansion. Therefore, the change in internal energy is equal to the minimum work required.