Topic 13.2 - Energetics II: Entropy Flashcards
What is the equation for the energy change (J) of a reaction?
Q = mc(delta)T
Q - energy in Joules, J
m - mass of solution, g (equivalent to the volume of solution as we assume density = 1)
(delta)T - change in temperature, K
What is the equation for the enthalpy change of reaction when you know the energy change of the reaction?
(delta) H = Q/n
(delta)H - Enthalpy change of reaction, kJmol(-1)
Q - energy in Kilojoules, kJ
n - Number of moles of limiting reagant
What is the equation for the enthalpy change of reaction when you know the enthalpy change of formation for your products and reactants?
(delta) H reaction = (delta) H products - (delta) H reactants
All units are kJmol(-1)
What is the equation for the standard total entropy change of a reaction?
(delta) S total = (delta) S system + (delta) S surroundings
All units JK(-1)mol(-1)
Under standard conditions
What is the equation for the standard entropy of the system?
(delta) S system = (delta) S products - (delta) S reactants
All units JK(-1)mol(-1)
Under standard conditions
What is the equation for the standard entropy of the surroundings?
(delta) S surroundings = - (delta)H reaction/ T
(delta) S - Entropy change of surroundings, JK(-1)mol(-1)
(delta) H - Enthalpy change of reaction, convert to Jmol(-1)
T - Temperature, K
What is the standard equation for Gibbs Free energy?
(delta) G = (delta) H reaction - T(delta) S system
What is the equation for Gibbs Free energy that includes the equilibrium constant of a reaction?
(delta) G = -RTlnKc
(delta) G - Gibbs free energy of the reaction, KJmol(-1)
R - Gas constant, 8.31 Jmol(-1)K(-1)
T - Absolute temperature, K
Kc - Equilibrium constant, from this equation you cant know the units of Kc
Under standard conditions
What is the equation for Gibbs Free energy that includes the Ecell value of a reaction?
(delta) G = -nFEcell
(delta) G - Gibbs Free energy change, KJmol(-1)
n - the number of electrons involved in the redox reaction
F - Faraday constant, 9.65 x10^4 Cmol(-1)
Ecell - Standard cell potential, V
What is the equation for the standard total change in entropy that includes the Ecell value of the reaction?
(delta) S total =(nFEcell)/T
(delta) S total - Total entropy change of the reaction, JK(-1)mol(-1)
n - the number of electrons involved in the redox reaction
F - Faraday constant, 9.65 x10^4 Cmol(-1)
Ecell - Standard cell potential, V
What is the definition of bond enthalpy?
The energy required to break 1 mole of that bond
What is the equation for the standard total enthalpy change of a reaction when you are given the bond energies?
(delta) H total = (sum of) Bonds broken - (sum of ) Bonds made
What sign does entropy always have? Why?
+ve, as particles are always in constant motion so there is always a degree of disorder
What is the definition of Entropy?
Entropy, S, is a quantitative measure of the degree of disorder of a system
When is the only time that entropy of a system = 0?
At Absolute Zero
What is the definition of a Spontaneous reaction?
A reaction that does not require any external input of energy in order to occur
What is the definition of a Feasible reaction?
A reaction that naturally tends to happen, even if it is very slow as the activation is high
What is required, in terms of entropy, for a reaction to be feasible?
- For (delta) S total > 0
Are spontaneous reactions always feasible?
Yes
Are feasible reactions always spontaneous?
No - A reaction can be thermodynamically feasible but not occur due to a very high activation energy (kinetics)