Enthalpy, Calorimetry, and Entropy Flashcards
How do you measure heat at a constant Volume?
Using a Bomb calorimeter. A device that measures the amount of heat released, or absorbed, in chemical reactions.
Change in E = q
Define heat Capacity. Note the formula, units, and what type of variable it is.
C is the raise in temperature of an object by one degree.
Units ( J / K )
Extensive state variable
What is the formulas for Molar Heat Capacity and Specific Heat Capacity?
Molar Heat Capacity: q = nC change in T
Specific Heat Capacity: q = mC change in T
Measuring Heat at a constant pressure
More convenient than constant volume.
H = qp
What is the Enthalpy equation? What type of function is it? And what are the units?
H = E + PV
H is a state function
KJ (extensive)
KJ / mol (intensive)
Is there energy released or required to form bonds? How about breaking bonds?
Formation of bonds: releases energy
(Stable state of atom is bonded)
Breaking of bonds: Requires energy
(Bond dissociation energy)
Define Heat of formation
The change in H when forming one mole of substance from elements in their standard states.
Ex: C(s,graphite) + O2 = 1CO2
What is Hess’s Law?
Change in H rxn = {Hproducts - {Hreactant
Define Entropy
A measure of energy dispersal. Associated with randomness of a system. S. Units J / K
Increase in disorder: S > 0
Decrease in disorder: S < 0
When is S supposed to increase?
- Increase in temp
- (s - l - g)
- number of molecules of gas increase from a reaction
- increase in molar complexity
What does it mean to be spontaneous?
Will continue reaction without any external reaction.
Define a Non- spontaneous process
Will not occur unless an external action is applied
What is the Second Law of Thermodynamics?
Suniv = Ssys + Ssurr
How is spontaneity related to Suniv?
Suniv > 0 means spontaneous reaction
Suniv = 0 means reversible; at equilibrium
Suniv < 0 means impossible reaction
What is Boltzmann’s relationship between entropy and microstates?
S = k ln W
k is Boltzmann’s constant
k = 1.38 e-23 J/K
