O.5 Flashcards
Entropy changes
What is the definition of entropy?
Entropy is the measure of disorder in a system. It measures how many ways particles and their associated energy can be distributed.
What can entropy tell us about a chemical reaction?
Whether a change is feasible or not, or whether it can happen spontaneously.
What are three processes that tend to happen spontaneously?
- Liquid evaporating
- Solids dissolving
- Gases mixing
What is a factor that drives chemical processes?
A tendency towards randomizing or disordering.
Reactions that involve which energy change tend to be spontaneous most times?
Exothermic.
When can a endothermic reaction happen simultaneously?
When it involves randomizing or disordering of reactants.
What symbol represents entropy?
S
Rank the four physical states (s) (l) (aq) (g) in order of highest entropy to lowest entropy.
(g), (aq), (l), (s).
What is commonly associated with high entropy?
Gas, high temperature, complex molecules.
What is commonly associated with low entropy?
Solid, giant covalent molecules, ionic lattice.
What value does the entropy of a substance always have?
Positive.
Why is high temperature associated with high entropy?
Because entropy is a measure of the distribution of energy in a system. The greater the energy within a system, the higher the entropy, because particles will collide and exchange energy.
What is the symbol representation of entropy change in a reaction?
∆S
When is ∆S positive?
When products are more disordered than reactants.
When is ∆S negative?
When products are less disordered than reactants.
What is the unit for entropy?
JK-1mol-1
What are two entropy changes do you need to take into account when predicting whether or not a change is feasible?
Entropy changes to the system and surroundings.
What is the symbol representation of the entropy change of system?
∆S sys, where sys refers to system.
What is the symbol representation of the entropy change of surroundings?
∆S surr, where surr refers to surroundings.
What is the symbol representation of the total entropy change for a process?
∆S total.
What is the equation for finding the total entropy change for a process?
∆S total = ∆S sys + ∆S surr
What value must ∆S total have for a reaction to be feasible or spontaneous?
Positive.
How do you calculate the entropy change of system?
Entropy of products take away the entropy of reactants.
What are two factors that the entropy change of surroundings depend on?
- The enthalpy change of the reaction, whether it is an endothermic process or an exothermic process.
- The temperature.
What is the equation used to calculate the entropy change of surroundings?
∆S surr = - ∆H/T
What unit should ∆H be quoted in when calculating ∆S surr?
Jmol-1, so simply multiple by a 1000 from kJmol-1.
What unit should temperature T, be quoted in when calculating ∆S surr?
K
At dynamic equilibrium, what must the value of ∆S total be?
0
Can entropy change tell you how fast a reaction will occur?
No, that’s why when entropy change is positive it is described as feasible: it may happen so slowly that for practical purposes it does not occur at all.
Under what condition will a reaction with a positive ∆S sys and a positive enthalpy change of reaction happen?
Above a given temperature.
Under what condition will a reaction with a positive ∆S sys and a negative enthalpy change of reaction happen?
Will always be possible.
Under what condition will a reaction with a negative ∆S sys and a positive enthalpy change of reaction happen?
Will never be possible.
Under what condition will a reaction with a negative ∆S sys and a negative enthalpy change of reaction happen?
Below a given temperature.
