Hydrogen Properties Lecture Notes 2024 PDF

Hydrogen and its compounds  Physical properties of hydrogen Discovered in 1766 – Henry Cavendish Iron The name “hydrogenium” means “water-forming” (A. Lavoisier) 1883 – liquefaction of hydrogen by Olszewski and Wróblewski. 1898 – liquefaction of hydrogen b...

Hydrogen and its compounds  Physical properties of hydrogen Discovered in 1766 – Henry Cavendish Iron The name “hydrogenium” means “water-forming” (A. Lavoisier) 1883 – liquefaction of hydrogen by Olszewski and Wróblewski. 1898 – liquefaction of hydrogen by the expansion method by Dewar. Hydrogen in the Universe 25% Helium 74% Hydrogen  Hydrogen in human body A living cell consists of 6 elements: C, H, O, N, P, S. These elements are called organogenic. They constitute about 97.9% of the mass of the human body.  Physical properties of hydrogen  colorless  odorless  tasteless  about 14 times lighter than air  very slightly soluble in water  soluble in some metals (e.g. palladium and platinum)  Ortho- and para- hydrogen These varieties are distinguished based on the direction of the spin of the nuclei, i.e. the spin vectors. Ortho - hydrogen molecules - parallel spins (+1/2 ; +1/2) or (-1/2; -1/2)) Para-hydrogen molecules - antiparallel spins (+1/2 ; -1/2) Under normal conditions, hydrogen contains 75% of the ortho variety and 25% of the para variety. As it cools, the para variety content increases, at 20 K it reaches 99.7%.  Atomic hydrogen At room temperature it exists for a very short time. It undergoes rapid recombination. It reacts with chlorine, bromine, iodine, oxygen, sulfur, arsenic and antimony to form hydrides. It reduces silver nitrate(V) to silver, chromates(VI) to chromium(III) salts, potassium manganate(VII) to manganese(II) salts.  Active hydrogen This is the state of hydrogen, at the moment when it is formed, e.g. in the reaction of zinc with hydrochloric acid (hydrogen in statu nascendi) It then reduces KMnO4 It has chemical properties similar to atomic hydrogen  Hydrogen - characteristics - 1H protium (light hydrogen, 99.985% atoms) - 2H deuterium (heavy hydrogen, 0.015% atoms) - 3H tritium (superheavy hydrogen, radiohydrogen, trace amounts) 1 : 1,5×10-4 : 10-18 In 1973, metallic (solid) hydrogen was obtained at a pressure of 2.8 Mbar. In these conditions, it exhibits superconducting properties.  Water and heavy water The difference in boiling points indicates that intermolecular hydrogen bonding is slightly stronger in D2O than in H2O. Compounds in which H atoms have been replaced by D are used for a variety of purposes, e.g. as solvents in 1H NMR spectroscopy. Many fully or partially deuterated compounds are available commercially, and the extent of deuterium labelling can be determined by mass spectrometry, density measurements (after conversion into water) or IR spectroscopy. The major industrial use of D2O is as a moderator in nuclear reactors; D has a much lower cross- section for neutron capture than H, and D2O is a suitable material for reducing the energies of fast neutrons produced in fission without appreciably diminishing the neutron flux.  Methods of producing hydrogen 1. 95% (87 million tons per year) of hydrogen comes from: steam reforming of natural gas, partial oxidation of methane, coal gasification. 2. Water electrolysis. 3. Hydrogen production from biomass (pyrolysis, gasification, hydrogen fermentation). 4. Biological methods – fermentation and biophotocatalysis. Hydrogen production  Obtaining water gas Water gas, i.e. a mixture of hydrogen and carbon monoxide, is obtained from oxygen-saturated steam and powdered coal or coke at a temperature of approx. 1000°C, e.g. in a continuous fluidized reactor. C + H2O H2 + CO Obtaining hydrogen from water gas Stage I Conversion, e.g. low-temperature catalytic reaction between carbon monoxide contained in water gas and water vapor at a temperature of 200-3000C. CO + H2O CO2 + H2 Stage II Elution of carbon dioxide under pressure using a hot potassium carbonate solution. Stage III Final purification of residual CO and other gases. Most hydrogen produced by steam-methane reforming emits a lot of CO2 – about 10 kilograms for every 1 kilogram of hydrogen. A cleaner way – to produce hydrogen by using renewable electricity like solar, wind or hydropower to split water  Water electrolysis 1,229 V Addition of a small amount of acid, base or salt 2H2O → O2 + 4H+ +4eˉ 2H2O + 2eˉ → H2 + 2OHˉ 2H2O → 2H2 + O2 Hydrogen production – laboratory methods  from acids by reaction with active metals Zn +2HCl ZnCl2 + H2 Hydrogen production – laboratory methods  from water by reaction with active metals 2K + 2H2O 2KOH + H2 Ca + 2H2O Ca(OH)2 + H2  from metal hydrides in reaction with water 2LiH + H2O 2LiOH + H2 CaH2 + 2H2O Ca(OH)2 + 2H2  from basis by reaction with amphoteric metals 2Al + 2NaOH +6H2O 2Na[Al(OH)4] + 3 H2 Advantages of hydrogen as an energy source 1. New environmentally friendly technology. 2. Minimizing the emission of toxins into the natural environment. 3. The variety of methods for obtaining hydrogen allows its use on a large scale.  Hydrogen-air fuel cell Cathode (+) porous graphite containing metallic nickel and nickel (II) oxide – oxygen reduction occurs on them. Electrode reactions: NaOH (50% (-) 2H2(g) → 4H+ (aq)+ 4e Anode (-) porous graphite containing (+) O2(g) + 4H+ (aq) + 4e → 2H2O (l) nickel as a filler (hydrogen oxidation occurs on these electrodes) Summary: 2H2(g) + O2(g) → 2H2O In the so-called cold combustion process of hydrogen and oxygen, electricity and heat are generated. Use of hydrogen  Airships Due to its low density, hydrogen was used to fill balloons and airships. One of the largest and most famous airships was the German Hindenburg, 245 m long and 41 m in diameter (the tanks held 200,000 m3 of gas). It had a speed of 135 km/h and could carry 72 passengers and 61 crew members. It flew to the USA and Brazil. On May 6, 1937, the airship burned down while docking at Lakehurst Airport (USA). 35 people died in the accident (13 passengers and 22 crew members). Today, they are used for tourist flights and as advertising banners, although there are plans to use their modernized version for military and transport purposes.  The position of hydrogen in the periodic table Similarity to alkali metals - group 1: One electron in the valence shell (one valence shell, Oxidation state +1 in compounds, Formation of compounds with nonmetals, Formation of compounds with halogens, Reducing properties  The position of hydrogen in the periodic table Similarity to halogens - group 17 Accepts 1 e and achieves a stable electronic configuration, Forms compounds in -1 oxidation state with metals, Similar ionization energy values (1312 kJ/ mol), Exhibits non-metallic nature, Occurs in the form of H2  Hydrogen properties The chemistry of hydrogen is defined by the following electronic processes: 1. Loss of a valence electron to form an H+ ion 2. Addition of an electron to form an H- ion 3. Formation of a single covalent bond, e.g. CH4 4. Formation of hydrogen bonds  Chemical properties of hydrogen 1. Very stable at normal temperature, flammable in air and in the presence of gaseous chlorine 2H2 + O2 2H2O (almost invisible, pale blue flame) H2 + Cl2 2HCl (radical reaction) Mixtures of hydrogen with air, oxygen and chlorine are explosive (these are so-called fulminant gases).  Chemical properties of hydrogen 1. The reaction of hydrogen with oxygen without a catalyst takes place at a flash point of approx. 6000C, in the presence of a catalyst, e.g. platinum, already at room temperature. 2. At elevated temperature, hydrogen also reacts with other non-metals H2 + S H2S 3. In the reaction of hydrogen with alkali metals at elevated temperature, hydrides are formed.  Hydrides Hydrides - binary compounds of hydrogen with another element Hydride naming: NaH - sodium hydride KH - potassium hydride CaH2 - calcium hydride Other names of hydrides (common names): CH4 – methane NH3 –azane - ammonia PH3 - phosphane - phosphine - phosphorus hydride  Hydride production 1. Direct synthesis from an element with hydrogen H2 + S → H2S 3H2 + N2 → 2NH3 Ca + H2 → CaH2 2. Exchange reaction 3 LiH + AlCl3 → AlH3 + 3 LiCl Division of hydrides according to their behaviour towards water, acids and bases  Acidic hydrides Hydrides of elements from 16 and 17 group They dissolve in water to form oxygen-free acids, e.g. HCl, HF, HJ, H2S which undergo dissociation HBr → HBr (aq) HF → HF(aq) They react with hydroxides to form salts HCl + NaOH → NaCl + H2O  Basic hydrides Alcali metal hydrides 2NaH + H2O 2NaOH + H2 Ammonia NH3 + H2O → NH4OH NH3 + HCl → NH4Cl Neutral hydrides CH4 i SiH4 They do not react with water Their low solubility in water is due to physical dissolution (mixing)  Division of hydrides according to the polarity of the bond 1. Hydrides in which the hydrogen atom has a partial positive charge, e.g NH3, H2O, HF - + ∂ ∂ M-H 2. Hydrides in which the hydrogen atom has a partial negative charge, e.g LiH, CaH2, B2H6, SiH4 + _ ∂ ∂ M-H 3. Amphoteric hydrides, e.g. AlH3, which can be an electron pair donor or acceptor  Division of hydrides according to the nature of the bond 1. Salt-type hydrides – (i.e. ionic) elements of groups 1,2 – s block 2. 2. Covalent (i.e. molecular) hydrides – elements of groups 14 – 17 and boron 3. 3. Metallic (i.e. interstitial) hydrides – elements of side groups – d block  Binary compounds of hydrogen H2 0 He BeH2 CH4 NH3 H2O HF wq BH3 41 Ne negative −74.8 −46.8 −243 −272 NaH MgH2 AlH3 SiH4 PH3 H2S HCl Ar −57 −75 −46 31 5.4 −20.7 −93 KH CaH2 FeH, GeH4 AsH3 H2Se HBr ScH2 TiH2 VH CrH Mn Co Ni CuH ZnH2 GaH3 Kr −58 −174 FeH2 92 67 30 −36.5 RbH SrH2 SnH4 SbH3 H2Te YH2 ZrH2 NbH Mo Tc Ru Rh PdH Ag CdH2 InH3 HI 26.6 Xe −47 −177 163 146 100 CsH BaH2 PbH4 BiH3 H2Po HAt LuH2 HfH2 TaH W Re Os Ir Pt Au Hg Tl Rn −50 −172 252 247 167 positive Fr Ra Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og ↓ LaH2 CeH2 PrH2 NdH2 PmH2 SmH2 EuH2 GdH2 TbH2 DyH2 HoH2 ErH2 TmH2 YbH2 Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Binary compounds of hydrogen Covalent hydrides metallic hydrides Ionic hydrides Intermediate hydrides Do not exist Not assessed Division of hydrides according to the nature of the bond  Salt-type hydrides 1. Salt-like hydrides are ionic compounds in which hydrogen occurs in the -1 oxidation state as H- 2. These compounds are formed from metals of group 1 and 2 of the periodic table (except Be) 3. 3. These are compounds with the composition MH (M = Li, Na, K, Rb, Cs) or MH2 (M = Ca, Sr, Ba) 4. They are formed in direct reaction with molten alkali or alkaline metals at a temperature 300 – 700 oC 400 °C 2Na(l) + H2(g) 2NaH(s) DH° = -112.6 kJ 400 °C Ca(s) + H2(g) CaH2(s) DH° = -181.5 kJ  Salt-type hydrides 5. They are crystalline solids with high melting points 6. At the melting point or slightly lower, they conduct electricity 7. Electrolysis of molten hydrides leads to the separation of H2 8. Ionic hydrides exhibit a basic character KH + HOH → KOH + H2 Covalent hydrides Covalent hydrides are formed by elements of groups 14–17 and boron. Most hydrides occur as gases ((NH3, PH3, H2S) or liquids (HF, H2O). These compounds are usually highly volatile. Covalent hydrides The stability of covalent hydrides in a given group decreases with the increase in the atomic number of the element combining with hydrogen and the deepening of its metallic character. HF – HCl – HBr – HI stability decreases, atomic numer increases HI – H2Te – SbH3 - SnH4 stability decreases, metallic character increases  Metallic hydrides They are formed as a result of the reaction of lanthanides and actinides and some transition metals of the d block with a variable amount of hydrogen. General formula: MHx. x Pd(s) + 2 H2(g) PdHx(s) Favored at higher Favored at lower temperature temperature  Metallic hydrides The approximate composition corresponds to the formulas: MH, np. VH, NbH, TaH MH2, np. TiH2, ZrH2, HfH2 MH3, np. UH3, PaH3 Copper hydride with wurtzite structure These hydrides have a lower density than the corresponding metals, and hydrogen is often reversibly adsorbed by the metal The chemical composition of metal hydrides is variable, so they are non- stoichiometric compounds hydrogen occupies an interstitial position in the metal lattice, forming a solid solution.  Hydrogen bonding The hydrogen bond is the ability of a hydrogen atom to bind two very electronegative atoms of N, O or F. A hydrogen bond is formed between an H atom attached to an electronegative atom, and an electronegative atom that possesses a lone pair of electrons. The hydrogen bond is partly (approx. 90%) electrostatic and partly (approx. 10%) covalent. IUPAC definition The hydrogen bond is an attractive interaction between the hydrogen from a group X - H and an atom or a group of atoms Y, in the same or different molecule(s), where there is evidence of bond formation.  Hydrogen bonding The average duration of a hydrogen bonding in water at room temperature is 3×10-12 s (3 ps). The energy of a hydrogen bonding is approx. 4 - 40 kJ/mol. Water Water molecules bonding by hydrogen bonds Hydrogen bond 47  Compounds that form dimeric units are carboxylic acids and amides: trans-[PdCl2L2] (L -pyridine-3-carboxylic acid) which forms infinite chains  Hydrogen bonding The most important phenomena caused by hydrogen bonding: Formation of open structures of water and ice Formation of the DNA double helix Formation of the α helix of proteins.  Hydrogen bonds Fig. 10.13 The left-hand diagram shows two units in one strand of DNA; DNA is composed of condensed deoxyribonucleotides and the four possible nucleobases are adenine (A), guanine (G), cytosine (C) and thymine (T). The right-hand diagrams illustrate how complementary base pairs in adjacent strands in DNA interact through hydrogen bonding.  Hydrogen bonding Hydrogen bonding affect: reduced vapor pressure increased boiling point increased viscosity low ice density hydration by water solubility in water rigidity of structure conformational organization (shape of biological macromolecules) Influence of hydrogen bonds  Hydrogen bonds Hydrogen bonding influences the properties of alcohols and phenols.