> See also: > - [[Chemical Reactions]] > - [[Chemical Equilibria]] > - [[Reaction Kinetics]] > - [[Chemical Energy]] # Chemical Thermodynamics > [!summary] Summary of Thermodynamics > Contents $\Delta H$ = **Enthalpy** (describes the heat content of a system) - $\Delta H < 0$ (-) → Exothermic (Releases Heat, Enthalpically Favored) - $\Delta H > 0$ (+) → Endothermic (Absorbs Heat, Enthalpically Opposed) $\Delta S$ = Entropy (degree of randomness/disorder) - $\Delta S < 0$ (-) → Increase in order - $\Delta S > 0$ (+) → Decrease in order (Ex: ) $\Delta G$ = Gibbs Free Energy (Capacity for work available) - $\Delta G < 0$ (-) → Exergonic (Spontaneous) - $\Delta G > 0$ (+) → Endergonic (Non-Spontaneous) - $\Delta G = 0$ → Equilbrium Free energy describes the *properties of a system*, including reactions or changes, rather than the properties of an individual molecule at any given moment in time. - $\Delta G$ is specific to individual reactions, with the corresponding variables (enthalpy/entropy) describing the resulting “changes within the system” that occur ![[Pasted image 20240129220238.png]] Standard Free Energy Change - The maximum amount of energy available from the system for useful work under standard conditions A reversible chemical reaction that is exergonic in the forward direction will be endergonic in the reverse direction Thermodynamics $\Delta G\degree^{\prime} = \Delta H - T \cdot \Delta S$ > [!important] **Thermodynamics vs Kinetics** > The sign (+/-) and magnitude of the free energy change for a reaction does not indicate how fast this reaction can proceed Activation energy can be best described as the amount of energy needed to bring molecules together in the correct way to reach a transition state ### Exothermic vs Endothermic Matter undergoing chemical reactions and physical changes can *release* or *absorb* heat. > - **Exothermic:** A change that **releases heat** > - *Ex: A gas welding torch (oxyacetylene torch) uses an exothermic combustion reaction to produce an immense amount of heat to melt/cut through objects.* > - **Endothermic:** A change that **absorbs heat** > - *Ex: A cold pack which, when activated, causes an endothermic chemical reaction to occur that absorbs heat, and thus leads to the sensation of feeling cold.* ## Standard States ## Factors Affecting Equilibrium > See also: > - [[Chemical Equilibria]] ![[Pasted image 20240129220337.png|400]] ![[Reaction Kinetics.png|500]] Not all reactions will be affected by temperature in the same way. - (rust is an exothermic reaction) ### V’ant Hoff Plots The equation for Gibbs A V’ant Hoff Plot can be created to essentially visualize how the equilibrium constant (K) of a chemical reaction changes with temperature (T). > [!question] **V’ant Hoff Plot Analysis** > thanks jean :) > ![[Chemical Thermodynamics.png]] > > For the green line Essentially, we are trying to determine if the line crosses the x-axis as this would indicate a change in the sign of the equilibrium constant ## Reaction Kinetics In chemistry, **kinetics** refers to the rate at which a reaction is occurring #### Factors Affecting Reaction Rates - The chemical nature Five Main Factors: 1. Chemical Nature 2. State of Subdivision 3. Temperature 4. Concentration 5. Catalysts ---