Thermodynamics And Thermochemistry Flashcards
Heat of a reaction in a bomb calorimeter equation
qrxn = -C x ΔT
In an exothermic reaction at equilibrium, increasing the temperature will:
According to Le Chatlier’s principle, increasing the temperature of an exothermic reaction will:
Increase the heat (a product), shifting the equilibrium towards the reactants
As the concentration of the reactants increase, the Kc of the reaction will decrease
The rate of the forward and reverse reactions will increase causing the reaction to proceed at a faster rate
The higher the temperature, the more energy the molecules have to hit each other with enough force to cause a reaction
Increasing temperature causes reaction to proceed at a faster rate while its Kc decreases
Formula for calculating the enthalpy change from bond enthalpy values:
ΔH = ΣΔHbonds broken - ΣΔHbonds formed
Bonds broken = reactants and bonds formed = products —> breaking bonds require energy (+) and forming bonds release energy (-)
Equation that governs enthalpy for a homogenous system:
(All gas or all liquid) H = U + PV
U = internal energy
P = pressure
V = volume
enthalpy of a system of a gas (or liquid) is dependent on pressure, volume and internal energy
what is enthalpy?
enthalpy (H) is the amount of heat energy contained within a system: ΔH = Hproducts - Hreactants
endothermic
a process in which heat is transferred from surroundings to the system (surrounding will feel cold): ΔH > 0
exothermic
a process in which heat is transferred from the system to the surroundings (surrounding will feel hot): ΔH < 0
what phase changes are endothermic?
fusion, vaporization, sublimation
what phase changes are exothermic?
condensation, recrystalization and deposition
conduction
the transfer of heat via direct contact
convection
the transfer of heat due to motion of a liquid of gas
radiation
the transfer of heat via electromagnetic radiation
what is the equation used to determine whether expansion or compression when referring to gaseous systems?
ΔE = q + w
w = -PΔV
ΔE = change in internal energy
q = heat
w = work
P = pressure (always a positive value)
ΔV = change in volume
when work is a positive value, the means ΔV is a ________ value and the volume has been ________
negative, decreased –> the surrounding is doing work on the system to compress it
decreasing volume compresses it
when work is a negative value, that means ΔV is a ____ value, and volume has been ________
positive, increased –> system is doing work on the surrounding causing it to expand
increasing volume expands it
what is specific heat (C)?
- the amount of energy that is required to raise the temperature of 1.0 gram of a substance by 1°C
- units are J/g °C
- specific heat varies from one substance to another and between phases of a substance
equation for calculating specifc heat of a substance and q (heat) it absorbs or releases and its mass:
q = mcΔT
* q = heat absorbed or released by substance
* m = mass of the substance (grams)
* C = specific heat of a substance
* ΔT = change in temperature of a substance
only used when calculating the q of a substance not undergoing a phase change (ex: increasing the temperature of water from 20°C to 90°C, water is a liquid at both temperatures and therefore it is not undergoing a phase change
equation for calculating the heat requirement while a phase change is occuring:
q = (m)ΔH
* ΔH = kJ/mol
* mass = mole
* if phase change involves conversion of solid to liquid then ΔHfusion will be used etc.
mass must be converted to moles!
second law of thermodynamics:
the entropy of the universe is always increasing (the universe is becoming more and more disordered)
ΔG: (+)
ΔH: (+)
ΔS: (-)
-TΔS: (+)
nonspontaneous
ΔG: (-)
ΔH: (-)
ΔS: (+)
-TΔS: (-)
spontaneous
ΔG: (+/-)
ΔH: (-)
ΔS: (-)
-TΔS: (+)
high temp: nonspontaneous
low temp:spontaneous
ΔG: (+/-)
ΔH: (+)
ΔS: (+)
-TΔS: (-)
high temp: spontaneous
low temp: nonspontaneous
-ΔG° means K is:
K > 1 products are favored at equilibrium
+ΔG° means K is:
K < 1 reactants are favored at equilibrium
