Thermodynamics Flashcards
IDEAL GASES
PV = nRT
Gas constant (R)
8.3145 LkPa/Kmol
What does a high temp correlate to for pressure?
A higher temperature would increase the kinetic energy of the atoms.
Therefore the atoms would move faster and collide more (INCREASING PRESSURE)
What does a low temperature correlate to for pressure?
A low temperature would mean that the atoms have a low kinetic energy and therefore MOVE SLOWER.
Less Collisions = Lower pressure
1 ATM
101325 Pa
or
101.325 kPa
STP
Standard Temperature & Pressure.
* 0°C or 273 k
* 1 ATM
ΔU
- ΔU = q + w
- ΔU = q +pΔV
- ΔU = C x ΔT
How would ΔU be demonstrated if the surroundings gain 10.80kJ ?
ΔU = - 10.8 kJ
negative value
How would ΔU be demonstrated if the system gains 10.80kJ ?
ΔU = 10.8kJ
positive value
First law of thermodynamics
ΔU = Q - W
Precision
The consistency of results with each other
Accuracy
The consistency of results with the true value
In regard to entropy, how does it determine the direction of a reaction?
A reaction will always proceed in the direction of increasing disorder .
TRUE OR FALSE
A reaction proceeds in the direction of increased orderliness
FALSE
A reaction always proceeds in the direction of increased disorder.
Define…
Entropy
The degree of measure of disorder in a system.
TRUE OR FALSE
Generally, in high temperatures there is a higher level of disorder
TRUE
Second law of thermodynamics
The change in entropy of a system must be greater than 0 for a spontaneous change to occur.
- ΔS_tot = ΔS_sys + ΔS_sur < 0: non-spontaneous
- ΔS_tot = ΔS_sys + ΔS_sur > 0 : spontaneous
TRUE OR FALSE
During a spontaneous change in an isolated system, the entropy decreases.
FALSE
For isolated systems, the entropy always increases during a spontaneous change. ΔS_tot > 0
Change in entropy [ΔS]
- ΔS = q_rev / T
- ΔS = ΔH / T
TRUE OR FALSE
There is NO DISORDER at 0 kelvin
TRUE
Third law of thermodynamics
There is no entropy at absolute zero.
Formula
Gibbs free energy
- G = H - TS
- ΔG = ΔH - TΔS
Criterion of spontaneity
ΔS
* ΔS > 0 : Spontaneous
* ΔS < 0 Non-spontaneous
ΔG
* ΔG < 0 : Spontaneous
* ΔG > 0 : Non-spontaneous
Coupled reactions
Reactions that are energetically unfavourable can be ‘coupled’ with favourable reactions.
This can be achieved when the overall change in standard gibbs free energy is negative (therefore spontaneous/favourable)
Δr_G°
Δr_G° = -RT lnK
R (universal constant) = 8.31 J/Kmol
TRUE OR FALSE
At equilibrium ΔrG = 0
TRUE
Δr_G
Δr_G = Δr_G° + RT lnK
Equilibrium constant [K]
K = ( C ^c ) ( D ^d )/ (A ^a) ( B ^b)
Molar gibbs energy
Gm = G/n
- n = number of moles
- G = Gibbs free energy
Formulas…
Enthalpy
- H = U + PV
- H =
Triple point
The point in which the substance exists in all three phases at the same time in equilibrium.
Critical point
The temperature and pressure point on a phase diagram where the LIQUID and GASEOUS phases of a substance merge together into one substance called the supercritical fluid
Gibbs phase rule
The number of intensive variables that must be defined to determine the state of a system.
F = C - P + 2
Intensive variable
A variable that is NOT dependent on the quantity of the system (e.g. water)
E.g. : Pressure, Density, Temperature
Extensive variable
A variable that is dependent on the quantity of the system
E.g. : Volume, Mass, number of moles
TRUE OR FALSE
Determining a state requires all the variables of a system
TRUE
Gibbs phase rule formula
F = C - P +2
- F = # of intensive variables
- C = # of components
- P = # of phases
Clausius-Clapeyron equation
Δln p / ΔT = Δ_evap_ H / RT^2
chemical potential
μ_A = μ°_A + RT lnX_A
How can you determine the gibbs free energy of a reaction?
G = (n_A)(μ_A ) + (n_B)(μ_B)
TRUE OR FALSE
Raising the temperature on an exothermic reaction will shift the equilibrium to the right
FALSE
There will be more heat on the product side so the equilibrium will counter by shifting to the reactants / left
Van’t Hoffs equation
Normal
ln(K2/K1) = ΔH/R (T2-T1/T2T1)
Van’t Hoff equation
In respect to ΔH
ΔH = R ln(K2/K1) (t2t1/t2-t1)
Clausius-clapeyron equation
Ln(P2/P1)= ΔH/R (T2-T1/ T2T1)
* P = vapor pressure
TRUE OR FALSE
Increasing the temp for an Endothermic reaction shifts to the right
TRUE
TRUE OR FALSE
The reaction shifting to the reactants means the reactants decrease
FALSE
The reactants will increase if the reaction shifts towards them.
Le chatelier’s principle
Endothermic reaction
* Increase temp = more products
* Decrease temp = more reactants
Exothermic reaction
* Increase temp = more reactants
* Decrease temp = more products
