2 - Thermodynamic Concepts and Colligative Properties Flashcards
(33 cards)
What is Enthalpy (H)?
The heat flow into the system while at constant pressure. Often referred to as heat content.
What is a useful way to imagine the Change in Enthalpy?
The change in energy of the system due to the difference in the initial and final bond energies in a reaction.
What is entropy?
Qualitatively a measure of evenness of energy distribution.
Quantitatively a measure of the unavailabilty of a system’s thermal energy to do mechanical work.
What is the second law of thermodynamics?
Spontaneous change in an isolated system is always accompanies by an increase in entropy.
Alternatively; a system with constant volume and internal energy will adopt a conformation that maximises its entropy.
What (qualitatively) is Gibbs free energy?
The maximum amount of energy in a system that is available to do non-mechanical work under constant temperature and pressure.
What, technically, is the qualitative definition of temperature?
The measure of how much the internal energy of a system with constant volume changes when the entropy changes.
What is the heat capacity of a system?
How much the energy changes with varying temperature.
Alternatively heat supplied to a system divided by change in temperature, at constant volume and pressure.
What two ways can heat capacity be quantified?
Cp - Change in enthalpy per change in unit temperature, at constant pressure.
Cv - Change in internal energy per change in unit temperature, per unit volume.
What assumptions are made when calculating heat capacity?
That the heat capacity itself does not change with temperature, which is not always true.
Also that the heat transfer is quasi-static.
What are intensive and extensive properties.
Intensive properties are independent of the amount of the substance, extensive properties change with an increase or decrease in the amount of a substance.
Is heat capacity an intensive or extensive property?
Extensive, as more energy is required to increase the temperature of more substance by the same degree.
What two ways are heat capacity made into an intensive property of a substance?
Specific heat capacity - energy required to raise the temperature of 1kg of a substance by 1 degree.
Molar heat capacity (Cp,m) - energy required to raise the temperature of 1 mole of a substance by 1 degree.
What equation defines the Standard Equilibrium Constant, K°, and also is notable for relating thermodynamic quantities to chemical ones?
ΔG° = -RT ln(K°)
What are the chemical standard state conditions?
1 bar 298.15K (not technically a requirement, but assumed) 1 MolKg‾¹ Hence pH0 when H+ is involved All assuming ideal-dilute conditions.
What values are different for biological standard states?
pH7 used
1E-7 MolKg‾¹
By finding equilibrium at constant temperature and pressure what is a system doing?
Adopting the conformation with the lowest Gibbs Free Energy.
What values are Gibbs Free Energy dependent upon?
Temperature
Pressure
Moles of each component of a system
What provides thermodynamic driving force for a reaction?
A reduction in free energy (-ΔG).
Describe the phenomenon of equilibrium in terms of Free Energy.
G changes differently with the number of moles of each reaction participant. Whenever G is not at a minimum it can reach a lower value by changing the composition of the reaction participants until it is its lowest value at the given temperature and pressure.
What is the chemical potential of a component?
How much the free energy of the system will change when the amount of the component changes.
i.e.; the slope of the free energy when plotted against changing number of moles.
What are the relative chemical potentials of two components of a system at equilibrium?
Equal across all phases.
µA = µB
What important factor is not technically part of the standard state definition?
Temperature.
What are colligative properties?
Properties of a dilute solution that depend upon the nature of the solvent and the amount of solute but NOT on the nature of the solute.
Why do colligative properties arise?
They arise solely due to the reduction in chemical potential of the solvent as a result. This is a purely entropic effect, being based on the number of solute particles.
