Chemical Thermodynamics Flashcards
Define Internal Energy
The sum of potential and kinetic energies of a system
What are Heat and Work Examples of ?
Energy Transfer
Define Heat Transfer
Flow of energy between two systems in thermal contact with different temperatures
Define Work
Transfer of an energy using a force
What are the dimensions of a Joule
kg M^2 s^-2
What is Change in Internal Energy
Transfer of energy from heat + transfer of energy from work
q+w
What is Specific heat Capacity?
Heat required to raise the temperature of a gram of material by 1 kelvin .
Calculate the energy required to brew a single cup of tea, 350ml of tap water 283K , is brought to 371K.
Water = 1gcm^-3
cp(water) = 75.2J
What is the Equation for Change in Enthalpy at constant pressure
Delta Enthalpy = Delta Internal Energy + pressure * Change in volume
Delta H = Delta U + P Delta V
What is Enthalpy
Heat flow of a system at constant pressure
Derive that Enthalpy is equal to heat flow of a system at constant pressure
Delta H = Delta U + P Delta V
Delta H = q + w + P Delta V
P Delta V = work done by the system against the surroundings
w = work done by surroundings on the system
Hence Delta H = q
At constant volume what is the Enthalpy?
at constant volume the container the gas cannot thermally expand
Hence work done on the system by the gas is zero.
so Delta H = Delta U = q
What is Enthalpy of Formation
Exo or Endo?
The enthalpy change when 1 mol of a compound is formed from its element in their standard states under standard conditions
2Na(s) +O2(g) -> Na2O(s)
Exothermic
What is Enthalpy of combustion
Exo or Endo?
The Enthalpy change when 1 mol of a substance is completely burnt in oxygen under standard conditions with all reactants and products are within their standard state.
H2(g) + O2(g) -> H2O(g)
Exothermic
What is the Equation for heat transfer at constant pressure?
q = M C Delta T
q = n C(p) Delta T
Where M = mass , C(p) = Pressure Heat capacity, n = number of moles. Delta T = Change in Temperature
What are Isothermal changes to a system?
Changes at Constant Temperature
What are Adiabatic Changes to a system?
Changes with no energy transfer via heat across the system boundary
How do you calculate Entropy , using the number of microstates and the Boltzmann constant
S = K(b) ln(Microstates)
what are microstates
collection of particles assuming the same energy.
In a spontaneous reaction, entropy can __________________________________.
Either increase or remain the same.
Write and equation that explains the second law of thermodynamics
Change in entropy of surroundings =
-1 * Delta H / T
opposite to system
What is the equation for Change in Gibbs Free Energy
G = H - TS
Delta Gibbs = Delta Enthalpy - Temperature * Delta Entropy
What is important to remember in free gibs calculations
T is in Kelvin
in hess cycle , arrows go from below upwards
fill the table in
