Thermodynamics test Flashcards
What is thermochemistry?
The study of heats of reactions (enthalpy)
Exothermic
-Negative delta H
-Favorable
Endothermic
-Positive delta H
-Less favorable
What is thermodynamics?
The study of the spontaneity of reactions and the useful work that can be done by them.
What does thermodynamics depend on?
Enthalpy (heat of a reaction), entropy (messiness), and temperature
What is a spontaneous reaction?
One that occurs without outside intervention
What is entropy?
The measure of disorder in a system (messiness)
What results in greater entropy?
- Molecules with a lot of atoms, high molar mass
- Samples with a lot of molecules
- A phase change from a solid to a liquid to a gas/aqueous solution
- More moles of gas
- A change from low concentration to high concentration
- A change from low temp. to high temp.
When does entropy=0?
Only for pure crystalline solids at 0 Kelvin
What is the second law of thermodynamics?
For all spontaneous processes, the entropy of the universe increases
- Entropy of universe = Entropy of system + entropy of surroundings
When is a reaction more likely to be spontaneous?
If there is an increase in entropy
- Positive delta S = more entropy = favorable
- Negative delta S = less entropy = less favorable
What is electrochemistry?
The study of reactions that involve a transfer of electrons between species both spontaneously and not spontaneously
What oxidation number does an element have in its standard state?
0
What is the oxidation number of a monotomic ion (single atom with a charge)?
The charge of the ion
Ex. 2+ ion = oxidation # of 2
What oxidation numbers do nonmetals typically have?
Negative (but can be positive sometimes)
What oxidation # does oxygen typically have?
-2 but -1 in peroxide
What oxidation # does hydrogen typically have?
+1 but can be -1 when bonded to a metal
What oxidation # is fluorine always?
-1 (but other halogens vary)
What is the sum of oxidation #s equal to in a polyatomic ion?
The charge of the polyatomic ion
What is the sum of oxidation #s in a neutral compound?
0
What causes a reaction to be redox?
When the oxidation #s of the elements change
What is oxidation?
When a compound loses electrons
What is reduction?
When a compound gains electrons
What is a reducing agent?
The chemical species that loses electrons/donates them to another species in an oxidation reaction
What is an oxidizing agent?
The chemical species that accepts/recieves electrons from another species in a reduction reaction
Why do redox reactions happen?
If there is a difference between how much different species want electrons, then electrons will spontaneously move from one species to another
