Thermochemistry Flashcards
First law of thermodynamics
Change in internal energy (delta U) = Heat (Q) - Work (W)
Adiabatic process
No heat exchange
Delta U = -W
Isothermic process
Constant temperature
Delta U = 0 –> Q = W
Isobaric process
Constant pressure
Isochoric process
Constant volume
Delta U = Q
What are two process functions?
Heat (Q) and work (W)
1 cal = ? J
4200 J
When is enthalpy (delta H) = Q?
At constant pressure
Heat absorbed or released in a given process = ?
q = m.c.delta T
What is the specific heat of water?
1
Heat capacity = ?
m.c
Equation when using a bomb calorimeter?
q sample + q oxygen = (-) q surroundings (water)
Equation to use to find equilibrium temperature of two objects?
q hot = (-) q cold
Heat of phase change = ?
q = m. L (latent heat)
What is held constant in a bomb calorimeter?
Volume
What is held constant in a coffee-cup calorimeter?
Pressure
Enthalpy (Delta H) = ?
(-) ?
(+) ?
Heat transferred into or out of the system
(-) : exothermic
(+) : endothermic
What is the standard enthalpy of formation, DeltaHf?
Enthalpy required to produce one mole of a compound from its elements in their standard states.
What is the standard heat of a reaction equal to?
Delta Hrxn = Sum of Delta Hf products - Sum of Delta Hf reactants
What is Hess’ law?
Delta H = Delta H1 + Delta H2 + Delta H3 …
It works for all other state functions as well.
What is the bond dissociation energy?
Average energy required to break a particular type of bond between atoms in the gas phase
Equation for Gibbs free energy? Mnemonic with the fish!!
Delta G = Delta H - T. Delta S
Goldfish are horrible without tartare sauce
What is an exergonic reaction? What is Delta G?
Spontaneous: Delta G (-)
What is an endergonic reaction? What is Delta G?
Nonspontaneous: Delta G (+)
When is Delta G temperature dependent?
When Delta S and Delta H have the same sign
What is the standard gibbs free energy?
Delta Grxn = Sum of Delta G products - Sum of Delta G reactants
How to calculate the standard Delta Grxn from Keq?
Standard Delta G rxn = - RT ln. Keq
How to calculate the Delta Grxn from Keq and Q? How to estimate the sign of Delta Grxn?
Delta G rxn = RT ln (Q/Keq) = Delta G (standard) + RT.lnQ
If Q/Keq
What happens to the volume of a substance as it goes from solid to liquid? Why? What is the exception to this rule?
It increases because it becomes less dense
Water
How can the entropy change in a reaction be estimated? 2 factors
- number of moles of reactants and products:
a. decrease in moles = decrease in entropy
b. increase in moles = increase in entropy - phase changes
a. gas to solid = decrease in entropy
b. solid to liquid = increase in entropy
Are explosions spontaneous or nonspontaneous?
Spontaneous
What is the enthalpy of formation of an element?
Always 0
Which side of an exothermic reaction is favored at high temperatures?
Shift to the left!
How to apply Hess’ law to heats of combustion and heats of formation?
Heat of combustion = sum of the heat of formation of the products - heat of formation of the reactants
What is the heat of formation of O2?
0
What does the standard heat of formation represent?
The heat necessary to synthesize elements in their standard state
What unit to use for all of these equations?
Kelvin!
When asked which conditions are favorable to a certain reactions, what are the 2 things you should check?
Moles of gas
Exo or endothermic?
What is the equation to calculate entropy?
Delta S = Qrev / T
Qrev = heat gained or lost in a reversible reaction T = temperature
When energy is added to a system, does its entropy increase or decrease?
Increase
When energy is removed from a system, does its entropy increase or decrease?
Decrease
How to calculate the change in entropy of a system?
Add up the change in entropy of the different elements in the system
What is the work of a calorimeter equal to?
0
What is the effect on entropy when particles move from high concentration to low concentration?
Increase in entropy
If Delta G is (-), then what does this mean for Q?
Q is smaller than Keq
What does a negative change in entropy mean?
It decreases
Solvation layer formation effects on entropy? Free energy?
Entropy: decrease
Free energy is > 0 –> non spontaneous
What is favorable: increasing or decreasing entropy?
Increasing
When adding hydrophilic molecules to water, is entropy increased or decreased? How is free energy affected?
Increased
Free energy spontaneous
What is the Delta G of passive transport?
(-)
What is the Delta G of active transport?
(+)
What is Delta G standard ‘ ?
Standardized for neutral pH = 7
What is the pH for standard Delta G?
0
How can I use the first law of thermodynamics in the cellular environment?
Fixed volume and pressure, so Delta U = Q
What is the equation for the entropy of the universe? What does it mean?
Delta Suniv = Delta S system + Delta S surroundings > 0
Which means: the entropy of a system and its surroundings will NEVER decrease, it will always remain 0 or increase
At constant P and T, the entropy of a system will spontaneously increase
What does it mean in radioactive decay if there is no tissue damage?
There was no gamma emission
When does “all” of a sample is considered to have decayed?
7-8 half lives
Which nuclear decay can be detected on an atomic absorption spectrum?
Gamma radiation
