Chemistry: Thermodynamics Part 2
This flashcard set explains lattice enthalpy as a measure of the strength of bonding in an ionic lattice. It defines two types: lattice dissociation enthalpy, the energy required to separate one mole of a solid ionic compound into gaseous ions, and lattice formation enthalpy.
What is entropy a measure of
Disorder in a system
Key Terms
What is entropy a measure of
Disorder in a system
Symbol for entropy
S
Why are the values for entropy always positiv
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
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| Term | Definition |
|---|---|
What is entropy a measure of | Disorder in a system |
Symbol for entropy | S |
Why are the values for entropy always positiv | 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 |
|
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 |
|
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 |
|
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 |
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 |