Enthalpy and Entropy
An increase in entropy.
a) freezing of water
b) boiling of water
c) crystallization of salt from a supersaturated solution
d) the reaction 2 NO(g) = N2O2(g)
e) the reaction 2 H2(g) + O2(g) = 2 H2O(g)
What is (b) the boiling of water?
The dG and spontaneity of the reaction ½ A2 + 2 B2 + C = CAB4 if dH = −104 kJ and dS = −60.8 J/mol·K at 30 °C.
What is -85.6 kJ/mol and spontaneous?
The likely location of lithium in a galvanic cell of lithium and fluorine.
F2(aq) + 2e- = 2F-(s) E0 = 2.87 V
Li+(aq) + e- = Li(s) E0 = -3.04 V
What is the anode?
If dH and dS are both negative or both positive, then the sign of dG.
What is depends on the temperature?
dG° for the reaction at 25°C:
SnCl4(l) + 2 H2O(l) = SnO2(s) + 4 HCl(g)
dH° = 133.0 kJ and dS° = 401.5 J/mol·K
What is 13.35 kJ/mol ?
The reaction that represents a decrease in entropy.
a) Fe(s) = Fe(l)
b) Fe(aq) + S(aq) = FeS(s)
c) 2 Fe(s) + 3/2 O2(g) = Fe2O3(s)
d) HF(l) = HF(g)
e) 2 H2O2(l) = 2 H2O(l) + O2(g)
What is (c) 2 Fe(s) + 3/2 O2(g) = Fe2O3(s) ?
A reaction that is not spontaneous at low temperatures can become spontaneous at high temperatures if dH is this and dS is this.
What are dH is positive and dS is positive?
The Eo for the cell: 2Al3+(aq) + 3Cd(s) = 2Al(s) + 3Cd2+(aq)
Al3+(aq) + 3e- = Al(s) Eo = -1.66V
Cd2+(aq) + 2e- = Cd(s) Eo = -0.40V
What is -1.26 volts?
The temperature a given reaction becomes spontaneous if dH = +119 kJ and dS = +263 J/mol·K.
What is 452.4 K?
The true statement regarding the dissolution reaction described: A given chemical spontaneously dissolves in water at room temperature and the process causes the solution to become quite cold.
a) The process is exothermic.
b) Its solubility will be greater in warmer water.
c) dS° for the reaction is negative.
What is (b) the chemical's solubility is greater in warmer water?
This is true when a process is exothermic and not spontaneous.
a) dS > 0
b) dH > 0
c) dG = 0
d) dS < 0
e) dH = 0
What is (d) dS < 0 ?
The equilibrium constant for a given reaction at 298, given a dG of −36.2 kJ/mol.
What is 2.22 x 106?
The number of grams of silver produced when a current of 6.0 amps is passed through a solution of Ag+ for 1.5 hours.
What is 36 grams?
The signs of dG and dS for the process at 25°C: I2(g) = I2(s)
What are negative?
A reaction with a negative dG proceeds very slowly at room temperature for this reason, but can be sped up this way.
What is the reaction is under kinetic control (high activation energy) and add a catalyst to lower activation energy?
The entropy change for methanol going from a liquid to vapor, if the enthalpy of vaporization of methanol (CH3OH) is 35.3 kJ/mol at the boiling point of 64.2 °C.
What is 104.7 J/mol K ?
The substance that does NOT have a dG°f = zero
a) O2(g)
b) Br2(g)
c) H2(g)
d) Ca(s)
e) Hg(l)
What is (b) Br2(g)?
The correct electrochemical cell notation for the reaction:
3Sn+2 + 2Al(s) = 3Sn(s) + 2Al+3
What is Al | Al+3 || Sn+2 | Sn
The signs of dH, dS, and dG for the exothermic reaction:
X(s) + 2Y(g) = 3Z(g)
What are dH=negative, dS=positive, and dG=negative?
The hybridization, molecular geometry, and bond angles of ammonia.
What is sp3, trigonal pyramidal, and 107o?
dS for Cu(s) + 1/2 O2(g) = CuO(s),
given: SoCu(s)= 33.15 J/mol.K; SoO2(g)= 205.14 J/mol.K; SoCuO(s)= 42.63 J/mol.K
What is -93.09 J/mol.K ?
The spontaneity and value of K for the reaction:
H2(g) + 1/2 O2(g) = H2O(l) at 25oC, given dG = -237 kJ/mol
What is K = 3.50 x 1041 and spontaneous?
The number of minutes it take to electroplate 28.3g of silver at a constant current of 2.0amps from a solution of silver nitrate.
What is 211 minutes?
The signs of dH, dS, and dG for the following:
Pure sodium is placed in Cl2(g) and NaCl(s) is formed without the addition of additional energy.
What are dH=negative, dS=negative, and dG=negative?
The percent yield of O2 when 10g KClO3 produces 1.4g O2.
2KClO3(s) = 2KCl(s) + 3O2(g)
What is 35.9% yield?