energetics(II) Flashcards
(17 cards)
define entropy and its units
it is the measure of degree of disorder/randomness in a system. it is reflected in the no. of ways the energy in a system can be distributed through the motion of the particles.
units: J mol^-1 K^-1.
further elaborate on what entropy means.
a system that has a high degree of disorder/randomness is said to have high entropy, where there are more ways to distrbute the energy.
what does it mean when entropy change is greater than 0?
it means that there is an increase in disorder/randomness of particles in a system. this means that the final state is more disordered than the initial state.
what does it mean when entropy change is smaller than 0?
this indicates that there is a decrease in disorder/randomness of particles in a system, meaning that the final state is less disordered than the initial state.
how does entropy differs for different states? Elaborate.
gas» liquid > solid
from solid to liquid phase:
when a solid melts into a liquid, the volume change is negligible. However, the solid lattice is disrupted and there is greater disorder. the particles can now move about more freely and with greater speeds and there are more ways to distribute the energy and to arrange the particles. Hence, entropy increases and is greater than 0.
liquid to gas phase:
when a liquid vaporises/boils, the change is accompanied by an even greater increase in entropy. the particles can now move at very high speed with great disorder. there are also more ways to distribute the energy and also the particles have more ways to arrange the particles as they move more randomly in space. Hence, there is a larger increase in entropy where entropy is > 0.
how does entropy differ for different no. of particles? Explain why.
more particles > fewer particles
when the products of a reaction contain more gas molecules than the reactants, the entropy of the system increases as there are now more particles moving randomly and more ways to distribute the particles and energy.
how does entropy differ for different orders of a structure?
less ordered structure > more ordered structure
how does entropy differ for different temperatures? Elaborate.
high temperature > low temperature.
the higher the temperature, the more energy the system possesses. In general, an increase in temperature gives the system more energy to be distrbuted among the particles, hence creating greater disorder and entropy increases.
How does the expansion of volume for gaseous system results in an increase in entropy>
if a gas is under pressure, it spontaneously expands when the pressure is released. when the volume of the gaseous system increases, the entropy of the system will increase(> 0) because there are more ways to distribute the gaseous particles and energy in a larger volume.
how does mixing of particles(gaseous particles) result in an increase in entropy.
mixing of gases will always result in increase in entropy as each gas expands to occupy the whole container. there are more ways to distribute the gaseous particles and energy(not an increase in quantity of energy) in a larger volume.
describe the 2 changes that occur in dissolving an ionic solid to determine overall entropy change.
- Dissolving ionic solid in water involves the breaking down of the giant ionic lattice sutrcture of the ioinic solid and the hydration of the ions involved. Entropy increases(> 0) as the giant ionic lattice breaks down and the ions are free to move.
- the free mobile ions then form ion-dipole interactions with the water molecules, leading to a decrease in entropy (< 0) as the water molecules become more ordered around the ions.
Hence, overall entropy change depends on the magnitude of both entropy changes of solute and solvent involved during dissolution.
state the equation that links entropy with Gibbs free energy. Also state the units for Gibbs free energy
Gibbs free energy = enthalpy change - (Temperature x Entropy)
units: kJ mol^-1.
state assumption made using the above equation to calculate gibbs free energy at different temperatures.
enthalpy change and entropy change remain constant at different temperatures.
However, this assumption may not be valid considering the fact that both enthalpy and entropy are temperature dependent.
state what gibbs free energy<0 mean
spontaneous reaction(exogernic process where energy is relased from system to surroundings)
(occur without external energy)
state what gibbs free energy >0 mean
non-spontaneous reaction(endergonic process)
requires an input of energy.
state what gibbs free energy =0 mean
system is at equilibrium(forward and backward reactions are at equilibrium)
this means that there is no net reaction as both reactions occur at the same rate.
e.g. melting of ice at 273k.
state the 2 limitations of the Gibbs free energy.
- use of Gibbs free energy to predict spontaneity is valid only under standard conditions.
- Kinetics consideration: the use of Gibbs free energy to predict the spontaneity of a reaction only gives an indication of the thermodynamic feasibility, but noy kinetic feasibility.
