Equilibrium and Stress
Edward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
Resources Available
Exp. L: Equilibrium and Stress
Observations
• Fe(NO3)3
• NH4SCN
• KSCN• NaNO3
• H2SO4
• CuSO4
• Co(NO3)2
Each compound breaks into one type ofpositive ion (cation) and one type of negative ion.
What ions are formed?
What color was observed for each compound?
Observations
NO3- SCN- SO4
2-
Fe3+ colorless
NH4+ colorless
K+ colorless
Na+ colorless
H+ colorless
Cu2+ blue
Co2+ pink
Which ions are responsible for color?
Concentration Effects
Thiocyanatoiron(III) Ion System
Write a balanced molecular equation for this reaction.
Write a balanced ionic equation for this reaction.
Write a balanced net ionic equation for this reaction.
What species is responsible for the red color?
[reactants]
[products]
Thiocyanatoiron(III) Ion Equilibrium Mass-Action Expression
Q =[Fe3+] [SCN-]
[[FeSCN]2+]
Write the mass-action expression for theformation of the thiocyanatoiron(III) ion.
Fe3+(aq) + SCN-(aq) [FeSCN]2+
[FeSCN]2+ + Fe(NO3)3
What does adarker red color indicate?
Why does the solution turna darker red color?
[reactants]
[products]Q =
[Fe3+] [SCN-]
[[FeSCN]2+]= K?
What ions are added whenFe(NO3)3 is added to the solution?
Fe3+(aq) + SCN-(aq) [FeSCN]2+
[FeSCN]2+ + KSCN
Why does the solution turna darker red color?
[reactants]
[products]Q =
[Fe3+] [SCN-]
[[FeSCN]2+]= K?
What ions are added whenKSCN is added to the solution?
Fe3+(aq) + SCN-(aq) [FeSCN]2+
[FeSCN]2+ + NH4SCN
Why does the solution turna darker red color?
[reactants]
[products]Q =
[Fe3+] [SCN-]
[[FeSCN]2+]= K?
Fe3+(aq) + SCN-(aq) [FeSCN]2+
[FeSCN]2+ + EDTA
Why does the solution turna lighter red color?
[reactants]
[products]Q =
[Fe3+] [SCN-]
[[FeSCN]2+]
Fe3+(aq) + EDTA(aq) [FeEDTA]- + 4 H+(aq)
Fe3+(aq) + SCN-(aq) [FeSCN]2+
[FeSCN]2+ + water
Why does the solution turna lighter red color?
[reactants]
[products]Q =
[Fe3+] [SCN-]
[[FeSCN]2+]
Does the equilibrium shift?
Fe3+(aq) + SCN-(aq) [FeSCN]2+
Pressure Effects
Nitrogen Dioxide-Dinitrogen Tetroxide System
Nitrogen Dioxide - Dinitrogen Tetroxide
NO2(g) + NO2(g) N2O4(g)
NO
ON
O
ON
O
ON
O
O
Nitrogen Dioxide - Dinitrogen Tetroxide
0 sec 1 sec 10 sec
NO2(g) + NO2(g) N2O4(g)
[reactants]
[products]
Nitrogen Dioxide - Dinitrogen Tetroxide
Mass-Action Expression
Q =
Why does the gas initially get darker and then lighten?
PNO2( )2
PN2O4
NO2(g) + NO2(g) N2O4(g)
Dilution Effects
Tetrachlorocuprate(II) Ion
Tetrachlorocuprate(II) Ion
Which ion is responsible for the color in each solution?
Cu2+(aq)+ 4 Cl-(aq) [CuCl4]2-
Tetrachlorocuprate(II) Ion and Water
Deionized water causes the pale blue color,salt water gives a pale green solution.
top view
Cu2+(aq)+ 4 Cl-(aq) [CuCl4]2-
[reactants]
[products]
Tetrachlorocuprate(II) Ion Equilibrium Mass-Action Expression
Q =[Cu2+] [Cl-]4
[[CuCl4]2-]
Why does the addition of water change the solution color,but the addition of salt water have no effect?
Cu2+(aq)+ 4 Cl-(aq) [CuCl4]2-
Temperature Effects
Nitrogen Dioxide-Dinitrogen Tetroxide
Tetrachlorocobaltate(II) Ion
Nitrogen Dioxide - Dinitrogen Tetroxide
Is theequilibrium
reactionendothermic
orexothermic?
icewater
roomtemp
hotwater
NO2(g) + NO2(g) N2O4(g)
Nitrogen Dioxide - Dinitrogen Tetroxide
Mass-Action Expression
Q =
Why does the color change?
PNO2( )2
PN2O4
NO2(g) + NO2(g) N2O4(g)
Tetrachlorocobaltate(II) Ion
Which ion is responsible
for theblue ion?
Co2+(aq)+ 4 Cl-(aq) [CoCl4]2-
Tetrachlorocobaltate(II) Ion Equilibrium Mass-Action Expression
K =[Co2+] [Cl-]4
[[CoCl4]2-]
pink cobaltblue
When the solution is heated,is the equilibrium constant increasing or decreasing?
Co2+(aq)+ 4 Cl-(aq) [CoCl4]2-
04/21/23
04/21/23