Lecture 17- Thermodynamics 3 Flashcards
Thermodynamically favored process
- spontaneous
- proceeds without any assistance from outside the system
- Ex. Water evaporates at 25C, iron rusts with O2 and H2O
- NaCl dissolves in water
- A process that is thermodynamically favored in one direction is non-thermodynamically favored in the other direction
TFP exothermic
- exothermic reactions are often thermodynamically favored
- nature tends to favor processes that cause a reduction in energy
- In an exothermic reaction, the bonds in the products contain less energy than the bonds in the reactants. The excess energy is released as heat.
TFP endothermic
- endothermic reactions can be thermodynamically favored
- evaporation is thermodynamically favored
- dissolving soluble compounds is thermodynamically favored
entropy
- a measure of the disorder of a system
- a greater degree is favorable
- a positive value for ^S is favorable
^S=S(products)-S(reactants)
laws of thermodynamics
- The energy contained within the universe is constant
2. The entropy of the universe is constantly increasing
S>0
- melting
- vaporization
- reactions where the products are in the same phase as the reactants but contain more particles than the reactants
- making most solutions
- adding heat
- increasing volume of gas
- when products have more particles
- volume increases
calculating ^S
^S=sum n S(products) - sum n S(reactants)
How to tell if a process is thermodynamically favored
- exothermic reactions are favored so ^H0
Two methods for determining if a process is thermodynamically favored
- ^S(universe)- theoretical
2. ^G (Gibbs free energy)
^S universe
^S (universe)=^S (system) + ^S (surroundings)
- If ^S>0, the reaction is thermodynamically favored, its its negative then it won’t happen at all
Gibbs free energy
^G=^H-T^S
- G= free energy change KJ
- H=enthalpy change KJ, calculate using calorimetry and Hess’s law or the enthalpy of formation values
- T- temperate of system K
- ^S= entropy change KJ/K, calculate using entropy values
- If G
Temperature and Thermodynamic favorability
^H and ^S: - + =yes at all temps \+ - = no at all temps - - =yes at low, no at high \+ + = yes at high, no at low
Free energy of formation
^Grxn=sum n G(products) - Sum n G (reactants)
Find the ^S for the following reactions using the S values given
^S=sum n S(products) - sum n S(reactants)
calculate ^G
^G=^H-T^S