Answers to Questions |
Part 1 Questions
1. H-, examples: NaH, CaH2
2. (a) NaBH4; (b) LiAlH4; (c) CaH2
3.
protons neutrons
hydrogen
1
0
deuterium
1
1
tritium
1
2
4. abundance of deuterium: 1/6400
5. half-life = 12.5 years
6. hydrogen makes up 92% of all atoms in Universe and 73.9% of the Universe’s mass.
7. H2 is found as elemental hydrogen near volcanic areas, in water, H2S, amines and organic compounds.
8. example: Zn(s) + 2 HCl(aq)
H2(g) + ZnCl2(aq)
9. CH4 + H2O(g)
CO(g) + 3 H2(g) ("syn gas")
or
3 Fe(s) + 4 H2O
Fe3O4(s) + 4 H2
10. (1) synthesis of ammonia by Haber process; (b) hydrogenate vegetable oil to make margarine and greases; (c) to produce methanol (from syn-gas by the Fisher-Tropsch process)
11. (a)
Broke 4 C-H bonds: 4
x + 413 kJ
Broke 2 O-H bonds: 2
x + 467
formed one CO triple:
- 1072
Formed three H-H: 3 x - 432
TOTAL
DHo = +218 kJ
11 (b) DHf:
CH4 -74.8 kJ/molDHrxn = +206 kJ
H2O(g) -241.8
CO(g) -110.5
H2(g) 0
12.
Broke 3 C-C bonds
2 x + 347 kJ
Broke 2 C-H bonds
2 x + 413
converted three C-C singles
into C-C double bonds 3x+347 - 3 x 614
Formed one H-H
1 x - 432
TOTAL
DHo = +287 kJ
13. (a) H2+:
(ss)1(ss*)0
BO = 1/2;
(b) H2-:
(ss)2(ss*)1
BO = 1/2;
14.
(a) CaH2(s)
+ H2O(l)
Ca(OH)2(s) + 2 H2(g)
(b) H2(g) +
O2(g)
2 H2O(g)
(c) Na(s) + H2O(l)
2 NaOH(aq) + H2(g)
(d) C2H4(g)
+ H2(g)
C2H6(g)
(e) NaH(s) + HCl(aq)
NaCl(aq) + H2(g)
(f) K(s) + H2(g)
2 KH(s)
15. C(s) + H2O(g)
CO(g) + H2(g)
16. 0.99 g Mg
17. (a) dhydrogen
= 0.0890 g H2/L;
(b) dair = 1.29
g H2/L;
(c) ratio = 14.5:1