Math Gymnastics: What’s it Good For?
∆H°f
Math Gymnastics: What’s it Good For?
Standard enthalpies of formation
Appendix L – page A29
∆H°f
Math Gymnastics: What’s it Good For?
Standard enthalpies of formation
Appendix L – page A29
∆H°f
Math Gymnastics: What’s it Good For?
Standard enthalpies of formation
Appendix L – page A29
D
B
F
C
∆H°f
A
E
Math Gymnastics: What’s it Good For?
Standard enthalpies of formation
Appendix L – page A29
C⟶D
D
B
F
C
∆H°f
A
E
Math Gymnastics: What’s it Good For?
Standard enthalpies of formation
Appendix L – page A29
C⟶D
∆H°rxn = ∆H°fD - ∆H°fC
D
B
F
C
∆H°f
A
E
(has its electrons stolen)
p. 142
(has its electrons stolen)
0
p. 142
(has its electrons stolen)
0
0
p. 142
(has its electrons stolen)
0
0
+2
p. 142
(has its electrons stolen)
0
0
+2
-2
p. 142
(has its electrons stolen)
0
0
ΔH
+2
MgO
f
-2
= −601 kJ
p. 142
Sodium in water
2 Na (s) + 2 H2O (aq) ⟶ 2NaOH (aq) + H2 (g)
Sodium in water
2 Na (s) + 2 H2O (aq) ⟶ 2NaOH (aq) + H2 (g)
0
+1
Sodium in water
2 Na (s) + 2 H2O (aq) ⟶ 2NaOH (aq) + H2 (g)
0
+1
+1
+1
0
Sodium in water
2 Na (s) + 2 H2O (aq) ⟶ 2NaOH (aq) + H2 (g)
0
+1
-2
+1 -2 +1
0
Sodium in water
2 Na (s) + 2 H2O (aq) ⟶ 2NaOH (aq) + H2 (g)
0
+1
-2
+1 -2 +1
0
Electronegativity
Na = 0.9
H = 2.2
Sodium in water
2 Na (s) + 2 H2O (aq) ⟶ 2NaOH (aq) + H2 (g)
0
+1
-2
Predict energetics (∆H):
+1 -2 +1
0
Electronegativity
Na = 0.9
H = 2.2
Sodium in water
2 Na (s) + 2 H2O (aq) ⟶ 2NaOH (aq) + H2 (g)
0
+1
-2
+1 -2 +1
Predict energetics (∆H):
reactants
ΔH rxn = ∑ ΔH products
−
ΔH
∑ f
f
0
Electronegativity
Na = 0.9
H = 2.2
Sodium in water
2 Na (s) + 2 H2O (aq) ⟶ 2NaOH (aq) + H2 (g)
0
+1
-2
+1 -2 +1
Predict energetics (∆H):
0
Electronegativity
Na = 0.9
H = 2.2
reactants
ΔH rxn = ∑ ΔH products
−
ΔH
∑ f
f
)
H 2(aq )
Na(s)
H 2O(aq )
ΔH rxn = 2ΔH NaOH(aq
+
ΔH
−
2ΔH
−
2ΔH
f
f
f
f
Sodium in water
2 Na (s) + 2 H2O (aq) ⟶ 2NaOH (aq) + H2 (g)
0
+1
-2
+1 -2 +1
Predict energetics (∆H):
0
Electronegativity
Na = 0.9
H = 2.2
reactants
ΔH rxn = ∑ ΔH products
−
ΔH
∑ f
f
)
H 2(aq )
Na(s)
H 2O(aq )
ΔH rxn = 2ΔH NaOH(aq
+
ΔH
−
2ΔH
−
2ΔH
f
f
f
f
ΔH rxn = 2(−469 kJ ) + 0 − 2(0) − 2(−286 kJ ) = −366 kJ
Sodium carbonate in soda
Na2CO3 (aq) + 2H2O (aq) ⟶ 2NaOH (aq) + CO2 (g) + H2O (l)
Sodium carbonate in soda
Na2CO3 (aq) + 2H2O (aq) ⟶ 2NaOH (aq) + CO2 (g) + H2O (l)
PCO2
Sodium carbonate in soda
Na2CO3 (aq) + 2H2O (aq) ⟶ 2NaOH (aq) + CO2 (g) + H2O (l)
PCO2
Sodium carbonate in soda
Na2CO3 (aq) + 2H2O (aq) ⟶ 2NaOH (aq) + CO2 (g) + H2O (l)
PCO2
PCO2
Sodium carbonate in soda
Na2CO3 (aq) + 2H2O (aq) ⟶ 2NaOH (aq) + CO2 (g) + H2O (l)
PCO2
PCO2
Sodium carbonate in soda
Na2CO3 (aq) + 2H2O (aq) ⟶ 2NaOH (aq) + CO2 (g) + H2O (l)
PCO2
PCO2
Combustion of H2
O2 (g) + 2 H2 (g) ⟶ 2 H2O (aq)
Combustion of H2
O2 (g) + 2 H2 (g) ⟶ 2 H2O (aq)
ΔH rxn = 2ΔH fH 2O(aq ) − ΔH Of 2(g ) − 2ΔH fH 2(g )
€
Combustion of H2
O2 (g) + 2 H2 (g) ⟶ 2 H2O (aq)
ΔH rxn = 2ΔH fH 2O(aq ) − ΔH Of 2(g ) − 2ΔH fH 2(g )
ΔH rxn = 2(−286 kJ ) − 0 − 2(0) = −572 kJ
€
€
Combustion of H2
O2 (g) + 2 H2 (g) ⟶ 2 H2O (aq)
ΔH rxn = 2ΔH fH 2O(aq ) − ΔH Of 2(g ) − 2ΔH fH 2(g )
ΔH rxn = 2(−286 kJ ) − 0 − 2(0) = −572 kJ
€
€
Hydrolysis of water
2 H2O (aq) ⟶ O2 (g) + 2 H2 (g)
Combustion of H2
O2 (g) + 2 H2 (g) ⟶ 2 H2O (aq)
ΔH rxn = 2ΔH fH 2O(aq ) − ΔH Of 2(g ) − 2ΔH fH 2(g )
ΔH rxn = 2(−286 kJ ) − 0 − 2(0) = −572 kJ
€
€
Hydrolysis of water
2 H2O (aq) ⟶ O2 (g) + 2 H2 (g)
ΔH rxn = +572 kJ
Interchapter, Fig. 9, p. 262
Interchapter, Fig. 13, p. 264
Hydrogen Fuel Cell
Work!!