hydrogen Flashcards by Shreshtha Gupta

hydrogen occurs in its atomic form at

high temperature

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name hydrogen is given by

lavoiser
as hydro means water and gene means forming in greek

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hydrogen exhibits similar properties as of

alkali metals (group 1)
halogens (group 17)

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difference between alkali metals and h2

ionisation energy is very high
size is much small

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difference between halogen and hydrogen

less reactive
electron affinity is much low as of halogens

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predominant isotope of hydrogen

protium
1H1

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heavy hydrogen

deuterium
2H1 or D

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deuterium is found in terrestrial region in the form of

HD
0.0156% deuterium is mostly in ofrm of HD

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radioactive isoptope

tritium
3H1 or T

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tritium emits

low energy B- particles having half life period of 12.33 years

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most abundant element in the universe

dihydrogen
H2

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laboratory preparation of H2

granulated zinc with dil HCl acid or dil H2SO4
Zn + 2H+(dil) –> Zn2+ + H2
zinc with aqu alkali
Zn + 2NaOH –> Na2ZNO2 + H2

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granulated zinc with dil HCl acid or dil H2SO4

Zn + 2H+(dil) –> Zn2+ + H2

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zinc with aqu alkali

Zn + 2NaOH –> Na2ZNO2 + H2

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pure zinc is not used in laboratory prep as

it reacts slowly with H2SO4 and addition of some impurities enhances rate of rxn

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commercial production of H2

electrolysis of water
2H2O –> 2H2 + O2
electrolysis of aqu Ba(OH)2
electrolysis of brine
2Cl- + 2H2O –> Cl2 + H2 + 2OH-
action of steam on coke

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catalyst used in action of steam on coke

nickel
1270K

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action of steam on coke reactions

C + H2O –> CO + H2
nickel catalyst (1270K)

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water gas

CO + H2
synthesis (syn) gas

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CO + H2

water gas or synthesis gas

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when syn gas is produced from coke, it is known as

coal gasification

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water gas shift reaction

CO + H2O –> CO2 + H2
673 K
catalyst = FeCrO4

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catalyst used in water gas shift rxn

FeCrO4

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CO2 is removed in water gas shift rxn by

scrubbing with sodium arsenite solution
(NaAsO₂)

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nascent hydrogen

newly born hydrogen Zn + H2SO4 --> ZnSO4 + 2H

adsorbed hydrogen is also known as

occluded hydrogen

occluded hydrogen is also known as

adsorbed hydrogen

1. more active 2. stronger reducing agent than ordinary 3. hydrogen occupies hole in crystal lattice of metal like Pt/Au/Fe/Ni/etc.

atomic hydrogen is formed by

when H2 is heated at low pressure, it gets dissaciated in atomic H2

nuclear spin isomers

ortho and para hydrogen (spin isomers)

ortho hydrogen spin

same direction (nuclei spin) electrons opposite spin (pauli) +1/2 +1/2 = +1 triplet state

para hydrogen spin

opposite direction (nuclei spin) electrons opposite spin (pauli) +1/2 -1/2 = 0 singlet state

compare internal energy ortho/para hydrogen

para < ortho as resultant spin of ortho = 1 para = 0

relative proportion of ortho - para hydrogen at absolute zero temperature

pure para para:ortho = 1:0

relative proportion of ortho - para hydrogen at temperature of liquefction of air

equal ratio para:ortho = 1:1

relative proportion of ortho - para hydrogen at room temperature or elevated temperature

ortho major para:ortho = 1:3

compare thermal conductivity ortho-para hydrogen

para has 50% more than that of ortho para > ortho

compare melting point ortho-para hydrogen

ortho > para

ortho para conversion is slow without catalysts. some catalysts are

atomic H2 activated charcoal metals like Fe, Ni, Pt, W paramagnetic species like O2, NO, NO2, Co2+, Cr2O3

pure para hydrogen can be achieved at

-20 K

conversion of para to ortho hydrogen

1. heating at 800C or above 2. passing electric discharge through para-H 3. treatment with catalysts 4. mixing para-H with paramagnetic molecule like O2 5. mixing para-H with atomic hydrogen

mixing para-H with atomic hydrogen gives

ortho-H

reaction of H2 with halogens

H2 + X2 --> 2HX F, occurs even in dark H2 + F2 --> 2HF Cl, occur in presence of sunlight H2 + Cl2 --> 2HCl Br, only on heating H2 + Br2 --> 2HBr I, requires catalyst Pt H2 + I2 --> 2HI

H2 + I2 --> 2HI catalyst

Pt 673 K

reactivity of halogens with dihydrogen

F2 > Cl2 > Br2 > I2

H2 with dioxygen rxn

2H2 + O2 --> 2H2O exothermic

H2 with dinitrogen rxn

3H2 + N2 --> 2NH3 Fe catalyst 673K, 200atm haber's process formation of ammonia

catalyst used in habers process

3H2 + N2 --> 2NH3 Fe catalyst 673K, 200atm

H2 with metals rxn

yield hydrogen H2 + 2M --> 2MH M = alkali metal

2Na + H2 -->

2NaH

Ca + H2 -->

CaH2

H2 with metal ions and metal oxides

reduces metal ions and oxides (less active than Fe) into corresponding metal H2 + MxOy --> M + H2O

H2 + CuO -->

Cu + H2O endothermic

H2 + Pbo -->

Pb + H2O

H2 with unsaturated hydrocarbons

H2(g) + unsatu HC --> satu HC catalytic hydrogenation Ni catalyst 473K

C=C + H2 -->

CH3-CH3 Ni catalyst 473K

hydrogenation of vegetable oil

vegetable oil + H2 --> Fat(s) Ni catalyst 473 K

hydroformylation of olefins

olefin + CO + H2 --> aldehyde RC=C + CO + H2 --> RCH2CH2CHO aldehyde further reduce to alcohol RCH2CH2CHO + H2 --> RCH2CH2CH2OH Pt catalyst

CO + 2H2 --> catalyst also

CH3OH (L) Co catalyst

used as

1. metallurgical process 2. cutting and welding 3. rocket fuel 4. fuel cells

compare bond dissociation energy H2 D2 T2

H2 < D2 < T2

compare bond strength C-H ; C-D ; C-T

CH < CD < CT

compare dielectric constant H2O D2O

H2O > D2O

___ is obtained as a by product in fertiliser industry

D2O

______ is used as a moderator in nuclear reactor

D2O

____ is used for study of rxn mechanism

D2O

H2 with high purity is obtained through

electrolysis of warm Ba(OH)2 solution using Ni electrodes