Thermodynamics Part 2 Flashcards
What is entropy a measure of
Disorder in a system
Symbol for entropy
S
Why are the values for entropy always positive
Particles always have energy
Units of entropy
JK-1mol-1
What needs to be done when combining entropy with enthalpy
/1000
Factors which determine the entropy of a substance
- state of matter
- dissolving
- mixtures
- number of particles
What is the entropy trend in state of matter and why
Entropy increases solid>liquid>gas as they’re more disordered
Trend in dissolving solid + solvent> solution
Entropy increases
Trend in entropy in formation of mixtures
Entropy increases
Trend in entropy as number of particles increases
Entropy increases
How to calculate delta S
Sum of S(prods) - Sum of S(reacts)
Effect of temperature on entropy: entropy is zero at 0K as
The particles have no kinetic energy therefore no movement
Effect of temperature on entropy: why does entropy increase as temperature increases
Particles move more and become more disordered
Effect of temperature on entropy: why is the second increase in entropy much bigger than the first
Gas particles have far more disorder than liquid therefore the entropy change from liquid to gas if much greater than solid to liquid
What can the values for entropy change be despite S values always being positive
Either positive or negative
When is Delta S positive
When there is an increase in disorder
Examples of positive delta S
- dissolving
- increase in number of moles of gas
- melting
- boiling
Why is delta S positive when dissolving occurs
The solution is more disordered than the solvent and solute
Why is delta S positive when there is an increase in the number of miles of gas
More moles of gas are more disordered
When is delta S positive when melting occurs
Liquids are more disordered than solids
Why is delta S positive when boiling occurs
Gases are much more disordered than liquids
What is a positive delta S favourable in terms of
Entropy
When is delta S negative
When there is a decrease in disorder
Examples of negative delta S
- precipitation
- decrease in number of moles of gas
- freezing
- condensing
Why is delta S negative in precipitation reactions
The solid is less disordered than the aqueous ions
Why is delta s negative when there’s a decrease in the number of moles of gas
Less moles of gas are less disordered
Why is delta s negative when freezing occurs
Solids are led disordered than liquids
Why is delta s negative when condensing occurs
Liquids are much less disordered than gases
What is a negative delta unfavourable in terms of
Entropy
Units of enthalpy change
kJmol-1
What is delta H in an exothermic reaction
Negative
When is a negative delta H favourable in terms of
Enthalpy change
What is delta h in an endothermic reaction
Positive
What is a positive delta h unfavourable in terms of
Enthalpy change
How to calculate delta H for a reaction
Sum of delta H products - sum of delta H reactants
What three factors contribute to whether a reaction will be feasible at a given temperature
Temperature
Entropy change
Enthalpy change
What do the 3 factors that contribute to whether a reaction is feasible at given temperature combine to give
A new quantity called the Gibbs free energy change
Gibbs free energy change
Delta G = delta H- T delta S
What must delta G be for a reaction to be feasible
Zero or negative
Why must delta s be converted to kJK-1mol-1
The units of Delta g and delta H are kJmol-1
Does the sign of delta G tell us anything about the rate of a reaction
No, it only tells us whether a reaction is thermodynamically feasible
When may a reaction not happen even if it is thermodynamically feasible
If the activation energy is too high
Why am endothermic reaction can take place spontaneously at room temp: when does a spontaneous process oroceed
When delta g is less than or equal to 0
Why am endothermic reaction can take place spontaneously at room temp: what does TdeltaS have to be greater than for a reaction to be spontaneous at room temp
Delta H
Why can a relation with a negative (unfavourable) entropy change be feasible at room temperature
Even though delta S is negative, delta H is also negative
Formula relating the calculation of temperature at which a reaction becomes feasible
T= deltaH/deltaS
What do free energy graphs show
The relationship between free energy and temperature
What can free energy graphs be used to find
The temperature at which a reaction becomes feasible
What equation can we use for free energy graphs and why
The plot is always a straight line
Y=mx+c
