Entropy Flashcards
What is entropy?
The degree of freedom within a system. Particles that can move freely in any direction have a much higher entropy then particles that are constrained.
Describe the entropy of a solid
The atoms are in fixed positions, without any freedom to move, therefore the entropy is low.
Describe the entropy of a liquid
The atoms are free to move in any direction, but must stay close together, therefore the entropy is greater than in a solid.
Describe the entropy of a gas
The atoms are free to move in any direction and to move to any position, therefore the entropy is high.
What is the symbol and units for entropy?
S, measure in JK-1.
Order the enthalpies of any substance in its different physical states
S(solid) < S(liquid) < S(gas)
What is the standard entropy of a substance?
The entropy of one mole in a given physical state under standard conditions.
How to calculate the entropy change?
ΔS = S(all products) - S(all reactants)
What is the second law of thermodynamics?
Entropy will always tend to increase in any isolated system that is not in equilibrium.
How do combustion reactions go against the second law of thermodynamics?
The entropy change appears negative, but this is because heat energy is released to the surroundings. This increases the entropy of the surroundings, which compensates for the decrease in entropy within the reaction.
What is the Gibbs free energy equation?
ΔG = ΔH - TΔS
What if the free energy calculated is negative?
The reaction will occur spontaneously.
What if the free energy calculated is positive?
The reaction will not occur spontaneously and we may be able to cause it to occur by changing the temperature.
What are some endothermic changes?
Physical changes such as boiling or dissolving.
Chemical changes such as the thermal decomposition of some salts when gases are produced.
