Entropy and Free energy Flashcards
What is entropy?
a measure of how dispersed the energy in the system is or how disordered a system is
What is the symbol for entropy change?
DS
How does an increase in disorder lead to an increase in entropy (positive DS)?
increase in disorder among particles in a system increases the dispersal of energy and leads to an increase in entropy (positive DS)
How does disorder and entropy depend on the movement of particles in a system?
if they gain more freedom of movement - solid–> liquid and liquid–>gas
there is an increase in the number of accessible energy levels so entropy increases
What are the 2 things that disorder and entropy depends on?
the number of particles
the degree of freedom of movement of particles
How does disorder and entropy depend on the number of particles in a system?
same state but more moles are produced then entropy increases as there are more ways energy can be distributed
What are the units for entropy?
J k-1 mol-1
k = kelvin
Describe the disorder and entropy of solids
locked together in a regular lattice, so particles have very little freedom of movement and remain in this highly ordered arrangement
so a solid is a low entropy state
Describe disorder and entropy of liquids
particles have limited freedom to move around and partly disordered structure so they have an intermediate entropy
Describe disorder and entropy in gases
particles are free to move around so their distribution in space is contantly changing so is it a highly disordered state and a high entropy state
For what 3 different reactions will DS be positive?
melting
vapourisation
dissolution (dissolving a solid in a liquid)
the no. of gaseous molecules increases
How might dissolving ionic compounds in water form more organised structures and have a more negative DS?
ions attract water molecules very strongly and cause them to become more organised
What does a negative DS mean?
less disordered
What does a positive DS mean?
more disordered
What happens to entropy if the number of gas molecules increases in a reaction?
the entropy increases
How do you calculate DS?
DS = entropy of product - entropy of reactants
What is more favourable for a reaction in terms of disorder and entropy?
reaction will tend towards more disorder and increase entropy
How can an ethalpically unfavourable (endothermic) reaction still spontaneously react?
if the changes in entropy are overcome by the changes in enthalpy
What does a positive DS tell you about entropic feasibility of the reaction?
DS is positive so the reaction is entropically feasible
What does a positive enthalpy chage value tell you about the reaction feasibility?
the reaction is not enthalpically feasible
What are the 2 factors favourable for a feasible reaction?
a negative enthalpy change
a positive entropy change
What is free energy (G)?
the balance between enthalpy and entropy changes which allows us to predict whether a reaction is feasible
What is the equation for free energy change?
DG = DH - TDS
T - temp in kelvin
What does a negative DG or 0 value mean?
the reaction is feasible
