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CHM 104: EXAM 4
ΔS is __ for every spontaneous process
|
positive
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if ΔSuniv is positive, the reaction is
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spontaneous
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if ΔSuniv is negative the reaction is
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not spontaneous
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heat flows from system to surroundings = ?
ΔHsys = ?
ΔHsurr = ?
ΔSsurr = ?
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exothermic
-
+
+
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heat flows from surroundings to system = ?
ΔHsys = ?
ΔHsurr = ?
ΔSsurr = ?
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endothermic
+
-
-
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for spontaneity:
TΔSuniv = -ΔHsys + TΔSsys is greater than or less than zero?
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greater than
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for spontaneity:
-TΔSuniv = ΔHsys - TΔSsys is greater than or less than zero?
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less than
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equation for Gibb's free energy
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ΔG = ΔH - TΔS
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if ΔG is negative:
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reaction is spontaneous
increase in Suniv
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if ΔG is positive:
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reaction is not spontaneous
decrease in Suniv
reverse reaction is spontaneous
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when ΔG = 0 the system is at
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equilibrium
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best ΔGrxn
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exothermic and positive ΔS
ΔH = - (good)
ΔS = + (good)
ΔG is always negative so the reaction is always spontaneous
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what ΔGrxn will never happen?
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endothermic and negative ΔS
ΔH = + (bad)
ΔS = - (bad)
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what ΔGrxn is better at low temperatures?
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exothermic and negative ΔS
ΔH = - (good)
ΔS = - (bad)
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what ΔGrxn is better at higher temperatures?
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endothermic and positive ΔS
ΔH = + (bad)
ΔS = + (good)
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if K is large and ΔGrxn° is negative; which direction is favorable?
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forward
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oxidation is always accompanied by a
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reduction
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do oxidation numbers change?
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yes |
oxidizing agent
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gets reduced
gains electrons
becomes more negative
(causes oxidation of something by taking e-)
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reducing agent
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gets oxidized
loses electrons
becomes more positive
(causes reduction of something by giving e-)
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assigning oxidation #s:
free elements
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0 |
assigning oxidation #s:
monoatomic ion
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charge
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assigning oxidation #s:
in compounds, ox # of O = __ except with __ then it equals __
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-2
peroxides (H2O2)
-1
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assigning oxidation #s:
in compounds, ox # of H = __ except in __ ___ then ox # =
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1
metal hydrides
-1
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assigning oxidation #s:
halogens
F is always __
Cl, Br, I also __, unless with __ or __, then the other rules apply __
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-1
-1
F, O
first
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assigning oxidation #s:
molecules
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sum of ox #s = 0
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Anode is oxidation or reduction?
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Oxidation
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Cathode is oxidation or reduction?
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Reduction
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Cell diagram:
One line (l)
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Phase boundary
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Cell diagram:
Two lines (ll)
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Salt bridge
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Where would you clip the wire to on cell diagrams
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The ends
The solids
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Standard conditions for solutes and gases
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1.00 M and 1.00 atm
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sign of a spontaneous Eºcell
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positive (+)
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table:
top to bottom
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more likely to run as written
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table:
bottom to top
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more likely to run the reverse
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total charge
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nF
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when the oxidation v is positive what does that say?
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very favorable oxidation, but not a favorable reduction
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chemical energy to electrical energy is
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spontaneous
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electrical energy to chemical energy is
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not spontaneous
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another term for not spontaneous
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electrolysis
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for electrolysis, how much voltage has to be applied?
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whatever Eºcell is plus a little
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can you do electrolysis in water?
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no |
with electrochemistry you always get the reaction that's the (most or least) unfavorable
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least (easiest)
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can't do electrolysis if more negative than what number?
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-1.23 v
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what would happen if you did electrolysis and number was less than -1.23
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you'd make water
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