Spontaneous Reactions
A spontaneous reaction proceeds on its own once the activation energy (and other conditions) is reached.
- A naturally occurring reaction
- Example: Rusting of iron, this occurs under normal conditions in the environment
- Example: H2CO3 → CO2 + H2O
- Almost ALL of the mass in this reaction will be products
Entropy
Entropy (ΔS) is a measure of the randomness, or disorder, of the reactants or products. The universe wants to be in disorder, it takes energy to put things (molecules, atoms, particles) into a structured order (think of your bedroom, it takes energy to keep it clean). The universe tends towards chaos , so, spontaneous reactions are those that increase the amount of randomness, or disorder which means you will have a POSITIVE ∆SExample: a car will rust, degrade, and fall apart over time, it will NEVER unrust and become new again
How is entropy increased?
How is entropy increased?
- Solid → liquid → gas
- A substance → parts of the substance
- Fewer number of particles → greater number of particles
- Slower movement of molecules → faster movement of molecules
- Fewer substances → more substances
- Diffusion of one substance through another
Gibbs Free Energy
- Entropy (ΔS): Entropy is a measure of the randomness, or disorder, of the reactants or products
- Enthalpy (ΔH): Enthalpy is the change in thermal energy associated with a chemical reaction
- Gibbs Free Energy Equation relates enthalpy and entropy: ΔG = ΔH – TΔS
- G = Energy given off by a reaction, Gibbs Free Energy
- H = Enthalpy of the system
- S = Entropy of the system
- T = Temperature the reaction occurs at, in Kelvin
Watch the following video!
https://youtu.be/huKBuShAa1w
Gibbs Free Energy equation:
- ΔG = ΔH – TΔS
- This equation can be use to determine if a reaction is spontaneous, or non-spontaneous
- ΔG = ΔH – TΔS
- ΔG = -986 – 288 x .33 = -1081.04 kJ/mol
- It is negative, so you have a spontaneous reaction.