Thermodynamic and Equilibrium Chapter 18

• Thermodynamics is the study of the relationship between heat and other forms of energy involved in a chemical or physical process.
• The first law of thermodynamics is essentially the law of conservation of energy applied to thermodynamic systems
• The sum of kinetic and potential energies is equal to internal energy, U.
• $w =$$-PV$work formula
• Whenever a thermodynamic system undergoes a physical or chemical change, the change of internal energy, U, of the system equals the sum of heat and work done in that physical or chemical change
• Internal energy formula : U = q + w
• The enthalpy of a system is defined as the system's internal energy plus pressure times volume
• Enthalpy formula : H = U+PV
• q = H when there is fixed( constant) pressure
• H = products - reactants using the standard enthalpies of formation
• A spontaneous process is a physical or chemical change that occurs by itself
• Nonsponateous process is when energy is required and work would have to be expended
• Entropy, S, is a thermodynamic quantity that is a measure of how dispersed the energy of a system is among the different possible ways that a system can contain energy.
• Entropy and Enthalpy are state functions
• Change in entropy formula : ΔS = Sf - Si
• Second law of thermodynamics, which states that the total entropy of a system and its surroundings always increases for a spontaneous process.
• Heat flow is also a flow of entropy, because it is a dispersal of energy
• ΔS = entropy created + q/t - Heat flow at absolute T and during sponatneous chemical reaction
• ΔS > q/t - during a spontaneous process is a positive quantity
• The second law of thermodynamics: For a spontaneous process at a given temperature T, the change in entropy of the system is greater than the heat divided by the absolute temperature, q/T
• Entropy change for a phase transition (at equilibrium or very close) : ΔS =q/T
• Enthalpy change for a phase transition (at equilibrium): ΔH = 0
• ΔS >q/T = ΔH/T (spontaneous reaction, constant T and P)
• ΔH/T - ΔS < 0(spontaneous reaction, constant T and P)
• ΔH - TΔS < 0 (spontaneous reaction, constant T and P)
• ΔH - TΔS is negative - reaction is spontaneous left to right as written
• ΔH - TΔS is positive - reaction is non-spontaneous left to right as written, and spontaneous in reverse
• ΔH - TΔS is zero - reaction is at equilibrium
• Third law of thermodynamics states that a substance that is perfectly crystalline at 0 K has an entropy of zero
• The standard entropy of a substance or ion, also called its absolute entropy, S°, is the entropy value for the standard state of the species
• Entropy increases in the following situations : a reaction in which a molecule is broken into two or more smaller molecules, a reaction in which there is an increase in moles of gas, a process
• Entropy increases in the following situation

  1. a reaction in which a molecule is broken into two or more smaller molecules a reaction in which there is an increase in moles of gas, a process
• Free energy, G, which is a thermodynamic quantity defined by the equation
• ΔG = ΔH - TΔS - change in Gibb's energy
• If ΔG is positive, then the reaction does not occur spontaneously under standard conditions
• ΔG for a reaction is negative when the reaction is spontaneous
• ΔfG˚ is the free-energy change that occurs when one mole of a substance is formed from its elements in their reference forms (usually the stablest states) at 1 atm and at a specified temperature (usually 25°C)
• When ΔG° is a large negative number (more negative than about -10 kJ), the reaction is spontaneous as written, and reactants transform almost entirely to products when equilibrium is reached
• When ΔG° is a large positive number (larger than about 10 kJ), the reaction is nonspontaneous as written, and reactants do not give significant amounts of products at equilibrium
• When ΔG° has a small negative or positive value (less than about 10 kJ), the reaction gives an equilibrium mixture with significant amounts of both reactants and products