Questions et réponses en chimie sur chemistry.stackexchange

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Sélection de questions intéressantes

• How to balance more complex redox reactions? → Comment équilibrer des réactions redox complexes
• sp5 hybridization in cyclopropane
  • Is hybridization of the cyclopropyl anion sp5?
• What determines the coefficients in the wavefunction of a hybrid orbital?
• How do I figure out the hybridization of a particular atom in a molecule?
• HCH bond angle in cyclopropane and cyclobutane
• When can a molecule be considered freely rotating at room temperature?
• What is the definition of of 'compound', 'mixture', 'element' and 'molecule'?
  • cf. http://pubs.acs.org/doi/abs/10.1021/ed200269e
  • http://pubs.acs.org/doi/abs/10.1021/ed3004275
• Chemistry behind Gale's Coffee Maker in Breaking Bad
• Why do salts such as NaCl dissolve? → Pourquoi les sels tels que le NaCl se dissolvent dans l'eau ?
• Non bonded orbitals in water
• White powder observed after boiling water in electric kettle for many weeks
• Conflict Between Organic and Physical Chemists--explaining the intensities of IR absorptions
• Estimation of the bond angle of water
• What is the real difference between ∆G and ∆G°?
• Are non-exothermic explosions possible?
• Will a strong acid still dissociate “completely” even in the presence of a stronger acid?
• During a phase change in matter, why doesn't the temperature change?
• Does an onion completely remove “fresh” paint VOCs and other chemicals emitted?
• Why doesn't calcium carbonate dissolve in water even though it is an ionic compound?
• Why is the minus sign (-) not allowed in Chemistry?
• Reason behind Le Chatelier's principle
• maximum number of electrons each shell
• When is there hybridization and when is there no hybridization?
• Why calcium chloride is used to melt ice over sodium chloride
• Why do we write NH₃?
• Can you make napalm out of gasoline and orange juice concentrate?
• Why is Borax used as a primary standard? → Pourquoi le borax est-il utilisé comme standard primaire
• What is the origin of the “positive-to-negative” convention concerning dipole moments in chemistry?
• Is there a chemical reaction that speeds up when the temprature gets lower?
• CuCl2 has colour but CuCl does not
• Why is phenolphthalein an appropriate indicator for titration of a strong acid with a strong base? → Pourquoi la phénolphtaléine est un indicateur approprié pour le titrage d'un acide fort par une base forte ?
• Why does CaCO3 react with HCl, but not with H2SO4?
• Why is HCl a stronger acid than Acetic Acid?
• Why is adsorption exothermic
• Iron nomenclature differences between Iron(III) and Ferric
• Why do the atoms in molecular models have the colors they have?
• Can an atom have more than 8 valence electrons? If not, why is 8 the limit ?
• Is there a difference between NaCl or table salt (processed) and salt from the Himalayas?
• Weird Wikipedia Section on Oxidizing Behavior of Nitric and Sulfuric Acids
• During a phase change in matter, why doesn't the temperature change?
• How to calculate melting/boiling points at different pressures
• Why does entropy increase when the difference in temperatures is decreased?
• Why doesn't copper react with hydrochloric acid while the other metals do?
• Reaction of silver nitrate and hydrochloric acid
• How could a change in alkalinity explain Rio 2016 pool water turning green?
• Is a negative pH level physically possible?
• To which block of the periodic table does helium belong?
• Why does the ionization energy decrease anytime the atom size increases? → Pourquoi l'énergie d'ionisation diminue-t-elle lorsque la taille de l'atome augmente ?plugin-autotooltip__default plugin-autotooltip_bigPourquoi l'énergie d'ionisation diminue-t-elle lorsque la taille de l'atome augmente ?
  
  * Cf. chemistry.stackexchange : Why does the ionization energy decrease anytime the atom size increases? * Question gérée par S.C. 2019-2020
  
  L'énergie d'ionisation (EI) correspond à l'énergie qu'il faut appliquer pour arracher un électron à un atome. Le rayon atomique des atomes influence cette énergie d'ionisation de manière inversement proportionnelle.$1s^2 2s^2$$1s^2 2s^2 2p^1$
• Why do raisins bob up and down in carbonated water?
• Are any bonds broken when NO2 becomes N2O4?
• What is the physical basis for Hund's first rule?
• Entropy change when indistinguishable particles suddenly become distinguishable
• How do you melt metals with super high melting points?
• What is “heating under reflux”?
• How could I cause metal to rust rapidly?
• Is it possible for halogens to show oxidation states less than -1?
• Why does ice water get colder when salt is added?
• Pi electron stacking, how does it work?
• What exactly is a mole?
• How are the atomic orbitals for multi electron atoms obtained?
• Why can't alcohols form hydrogen-bonded dimers like carboxylic acids?
• What are oxidation states used for?
• Why do we use helium in balloons?
• Why would breathing pure oxygen be a bad idea?
• Why is the reduction by sugars more efficient in basic solutions than in acidic ones?
• Chemical bonding and dipole moment
• How do I type a simple chemical equation in Microsoft Word?
• How can I safely handle a concentrated (fuming) nitric acid spill?
• How to separate alloys?
• How does osmosis work?
• How does one tell if a specific molecule is acidic or basic?
• Why is ammonium a weak acid if ammonia is a weak base?
  • cf. What is the pKa of water? (chemistry libretexts)
• Ammonium Hydroxide Name
• pKa de l'ion hydronium ou oxonium…
  • How to calculate Ka for hydronium and Kb for hydroxide?
  • What is the pKa of the hydronium, or oxonium, ion (H3O+)?
• Why are snowflakes shaped as they are?
• Is there an easy way to find number of “valence electrons”?
• What is the difference between “atomic hydrogen” and “nascent hydrogen”?
• Can drinking a lot of water be fatal?
• How to determine number of structural isomers?
• Structure of Br3O8
• How do I figure out the hybridization of a particular atom in a molecule?
• What is the white substance left behind after boiling down water
• An introduction to “oxidation state”/“oxidation number”
• Does water have a chemical name?
• Do acids really donate a proton? → Les acides donnent-ils vraiment un proton ?plugin-autotooltip__default plugin-autotooltip_bigLes acides donnent-ils vraiment un proton ?
  
  * Cf. chemistry.stackexchange : Do acids really donate a proton? * Question gérée par S.N., étudiant 2019-2020
  
  Développement
  
  (lignes de développement uniquement - ici figurent qques mots clefs et symboles de type (..) pour définir les lignes directrices de l'argumentaire/l'explication)
• Is this a violation of Equipartition theorem?
• Why alkanes containing even number of carbons can be packed more efficiently than alkanes with odd number of carbon atoms?
• Choosing the right condenser
• Is there such a thing as an acid without a hydrogen?
• Why do different H+ in polyprotic acids have different K?
• What is charge density?
• How was it concluded that the H3O+ rather than H+ is the “acid” ion?
• Can other substances be dissolved in a saturated solution?
• Can sodium bicarbonate be considered an acid?
• Is it possible for a compound to be soluble in a mixture of solvents but not the individual solvents?
• Why doesn't tetraiodine exist?
• Is the term “heteroatom” reserved for exclusive elements?
• Why is it important to use a salt bridge in a voltaic cell? Can a wire be used?
• Why are dipoles “permanent/induced dipole permanent/induced dipole” and not just “permanent/induced dipole” once?
• In the bicarbonate ion, why can the hydrogen not bond to the carbon?
• Will KOH work in place of NaOH as the electolyte in the electrolysis of water?
• Why does chocolate melt so easily?
• Why does a substance with an endothermic heat of solution dissolve?
• What allows sulfur and phosphorus to expand their octet?
• Why does Zn react with NaOH?
• An ionic compound dissociates into 3 ions of 3 different elements?
• If polyethylene glycol (PEG) is hygroscopic, how does it protect wood?
• Relation between molar mass and van der Waals force
• Difference between electropositivity and electronegativity
• Why does whipped cream use nitrous oxide instead of nitrogen gas?
• What is the reaction between oxalic acid and potassium permanganate?
• A glass of water with ice-cubes in it. Where's the water the coldest; at the top or bottom?
• Why is it wrong to use the concept of “hybridization” while studying complexes?
• Why does mercury decolourise a gold ring?
• Saturated vs unsaturated fats - Structure in relation to room temperature state?
• What is the difference between D and L configuration, and + and −?
• Can I eat the lemons after I have used them as a battery?
• Explanation of Lemon Juice-Invisible Ink
• Percentage ionic character if electronegativity is given
• Reviving Li-ion battery in freezer?
• What volume does one mole of an ideal gas occupy? → Quel volume occupe une mole de gaz idéal
• What are the side effects of adding dry ice to a swimming pool?
• What is the pKa Range for weak acids and bases?
• What properties of carbon dioxide make it a greenhouse gas?
• Why is fluorine a gas, but lithium isn't?
• Freezing point of oxygen-18 water
• Why do branched chain compounds have lower boiling points than the corresponding straight chain isomers?
• Why do transition elements make colored compounds?
• Improving Elephant Toothpaste experiment
• What's the difference between reactant, excess reactant and limited reactant in a balanced equation?
• Michaelis-Menten mechanism of enzyme-catalyzed reactions
• Why add water first then acid? → Pourquoi faut-il toujours mettre l’eau en premier et l’acide ensuite
• What is the molecular structure of xenon hexafluoride?
• Choice of preferred IUPAC names
• What is the analogue of “molecule” for ionic compounds?
• What are the products of the dissociation of sodium bicarbonate in water? What is the relative pH of the solution?
• What is the difference between ignition temperature and flash point?
• Why are covalent bonds directional?
• Why do methane molecules have 15 degrees of freedom?
• What is K2O-nSiO2-xH2O?
• What do the different grades of chemicals mean?
• Reviving Li-ion battery in freezer?
• How to properly store acids at home?
• Does a diatomic gas have one or two vibrational degrees of freedom?
• Is it actually possible to dispose of a body with hydrofluoric acid?
• Na+ or Ca2+ . Which ion has the larger radius?
• How does water evaporate completely when at room temperature?
• Do electronic balance weighings still need to be corrected for buoyancy error?
• Most probable point for finding an electron in the 1s orbital of a Hydrogen atom
• Misleading features of Lewis Dot Representation
• Why are indicators used only in the form of dilute solutions?
• Is it correct to say that ethenol is an alcohol?
• What visual observations can confirm that a reactant is the limiting reagent?
• How exactly do sulfites prevent oxidation of wine?
• Is there a way to “electroplate” wood with copper?
• Elements which do not form oxides
• What is the differences between partial pressure and vapour pressure?
• The shapes of molecules
• Etymology of saturation degrees (-ane, -ene, -yne) in aliphatic compounds
• The impossibility of 100% ionic bond
• Arrows used in chemical reactions
• Dipole moment - calculation of percentage ionic character
• Is melting/boiling point of ionically bonded substance higher than of covalently bound?
• What happens to the argon in the Haber-Bosch process?
• How do I figure out the hybridization of a particular atom in a molecule?
• How do they ensure there is one electron on an oil drop in Millikan's oil drop experiment?
• Image of crystal structure
• Would the concentration of oxygen around fire increase as we get close to the fire (from the outside)
• What is the condensation point of water?
• Are children's sparklers based on a magnesium reaction?
• Oxidation of aluminum and manufacturing of electrolytic capacitors
• Why is entropy favorable?
• How is aqua regia stored?
• Why exactly does precipitation occur?
• What is the melting point of diamond?
• Why do we use J(J+1) instead of J² in the rigid body rotor energy equation?
• Le Chatelier's principle: Are there any exceptions?
• What is the difference between a coefficient and a subscript in a chemical equation?
• How do I calculate the degree of dissociation in equilibrium?
• Which is the most acidic hydrogen in vitamin C
• What is the carbon dioxide content of a soda can or bottle?
• Why do different substances have different boiling points?
• Why copper sulphate is a catalyst in this reaction
• Enrichment of D2O
• Why do we use helium in balloons?
• Positive or Negative Anode/Cathode in Electrolytic/Galvanic Cell
• What makes Coke acidic?
• Why do the melting and boiling points of the noble gases increase when the atomic number increases?
• Preparation of iodine solution
• What is the difference between ψ, |ψ|², radial probability, and radial distribution of electrons?
• Minimal basis for Li
• Volume of orbitals
• Why are metal oxides basic and non-metals' acidic or neutral
• What would be the effect of the addition of an inert gas to a reaction at equilibrium?
• Are metallic/ionic bonds weaker than covalent bonds?
• Which is the strongest base?
• Derivation of the Temperature Dependence of the Boltzmann Distribution
• How to find the hybridization of an atom in a molecule?
• What are the differences between diesel and unleaded gasoline?
• How to calculate the concentration H3O+ in a solution with pH=6.99?
• Why do we use helium in balloons?
• Why does potassium react more violently with water than lithium?
• What role does sulfuric acid play in the titration of oxalic acid and potassium permanganate?
• How do I extract cyanide from apple seeds?
• Why are there multiple lines in the hydrogen line spectrum?
• What is SPDF configuration?
• Why do we not generally have “enneane”?
• Which has stronger hydrogen bonds: water or ice?
• Why does adding salt to boiling water cause it to flare up suddenly?
• What bond exists in “red oxygen”, and can something similar happen with hydrogen?
• Why DNA is negatively charged and what makes it so?
• Melting points and boiling points of primary alcohols do not follow the same trend
• Differences between phenols and alcohols
• Why does carbon monoxide have a greater affinity for hemoglobin than oxygen?
• Why doesn't water burn?
• Half-Life of Radioactive Isotopes: Why? How?
• Would it be possible to destroy gold?
• are half of “H2SO4 pH sample problem” webpages just wrong, or am I wrong?
• How to name binary (inorganic) compounds given their chemical formula, and vice-versa?
• Why does C=O have a larger dipole moment than C-O?
• Why do most carboxylic acids have high pKa (~5) in spite of having a conjugate base ion that is stabilized by resonance?
• Search by CAS Registry name to obtain trackable accession: ie InChi?
• Calculate pH of a weak acid and weak base neutralization reaction
• What is the proof of complete ionic dissociation in water?
• What causes the “rotting fish smell”?
• Which chemical reactions don't involve bond breaking?
• What is a neutral atom?
• Difference between conformational, constitutional, and structural isomers and the same and different molecules
• Lewis structure for magnesium diboride
• Rules of naming ionic compounds
• Chemical equation that can be balanced in infinite number of ways?
• Would standing next to a pool of mercury do you any harm?
• Why does the melting point get lower going down the Alkali Metal Group with increase in atomic number?
• How can melting point equal freezing point?
• Difference between thermodynamic and kinetic stability
• What is the correct name of 3-isopropyl-4-methylhexane?
• How does chlorine in water evaporate?
• How to decide acidic or basic nature of oxides
• Why is it OH- and not HO-? (duplicate)
  • Why is methane's molecular formula conventionally “CH₄”, while water is “H₂O” (among others)?
• How is the light from a fire emitted?
• What is the strongest oxidising agent?
• Why don't we explode after drinking water?
• How to chose wavelength in spectrophotometry? How to use Beer-Lambert Law?
• Reason for the stronger acidic property of phenol than alcohol
• Why does wood burn but not sugar?
• How can the solid state structure of cyclopentadienyllithium be explained?
• Why do we use Δ to mean heating?
• Is there an easy way to remember charges on ions?
• How to find pH by mixing two solutions of different concentrations?
• Why can the acidic strength between H2S and HCl be explained on the basis of electronegativity but H2S and H2O can't?
• Does a neutral dimercury molecule exist?
• Properties of Water
• Which is anode and which is cathode?
• How could the ideal gas law be discovered from experiments on real gases?
• Why does the beryllium 2+ ion have a larger radius than a helium atom?
• Why does zinc react with sodium hydroxide?
• Why can a diamond be broken using a hammer if it's the hardest natural substance known?
• Can a long polymer chain interact with itself via van der Waals forces?
• Why proton concentration is divided by 10⁻⁷?
• Reaction between NaOH and CO2
• Flame Test Spectrograms Not Lining Up With Reality
• Why doesn't H₄O²⁺ exist?
• amu and g/mol relation
• Difference between shells, subshells and orbitals
• How do non-polar substances dissolve in non-polar solvents?
• Storing hydrofluoric acid before the invention of plastics
• When a candle burns, why does the top of wick glow if bottom of flame is hottest?
• Does the main washing effect of soap come from foam?
• Why does electrolysis of aqueous concentrated sodium bromide produce bromine at the anode?
• How is the potential energy between two atoms measured?
• Does concentration of salt increase or decrease rate of rusting?
• Tetrahedral or Square Planar
• What purpose does mercury dichloride have in fireworks?
• Why is it considered acid rain with pH <5.6?
• How do you explain pKa to non-professional?
• Why is only the carbonate anion used to precipitate Barium?
• What’s the biggest organic molecule that could have a smell?
• How to predict the decomposition products of for example barium carbonate?
• organophosphorus compounds - How to convert P2O5 concentration to H3PO4 concentration?
• everyday chemistry - Will alcohol or soap damage plastic or rubber?
• Covalent Bond/Hydrogen Bond
• Explanation for why nickel turns green in hydrochloric acid
• Is black tea a pH indicator?
• Calcium ion and sulfate did not form precipitate
• How do Precipitation Reactions behave in the Absence of Gravity?
• Heat involved in isenthalpic process
• Unexpected result (sodium hypochlorite & steel wool)
• Why does chlorine have a higher electron affinity than fluorine?
• Lewis Structure of OF+
• Why is O2 a biradical?
• Reason for the generation of London Dispersion Forces
• Why London Dispersion force is attractive not repulsive
• How are the number of tetrahedral voids twice the number of octahedral voids in a CCP structure?
• What are the correct resonance structures of nitrous oxide?
  • + question “Socratic” : What is the Lewis electron dot formula (Lewis structure) of Nitrous Oxide (N_2O)?
• atmospheric chemistry - Why does nitrous oxide have 300 times the global warming potential of CO2?
• experimental chemistry - How come water would not affect the results of a titration?
• gas laws - Pressure Vs Volume plot for real and ideal gasses
• aqueous solution - Taking volume contraction into account when mixing water with ethanol
• inorganic chemistry - Calculating pH of rain water
• nomenclature - What is a word for “atom or molecule”?
• everyday chemistry - How would I measure the Carbon Dioxide content in Coca Cola over a period of time?
• Software to assist drawing of complex, three-dimensional skeletal formula from scratch or from existing crystal structure
• How does acetone remove pencil marks?
• Neutralizing a sulfuric acid spill
• How quickly is converting a H2O + D2O mixture to HDO?
• Is anode actually ever negative?
• Dimethylethylamine or Ethyldimethylamine?
• Why does N(OH)3 not exist?
• membrane for a reverse osmosis desalination experiment
• Can someone intuitively explain the reason for the units of entropy (J/K )?
  • Why can entropy be measured in joules per kelvin?
• How does pH of soda drink vary with time
• Tools for Molecular Simulation
• What exactly is temperature?
• How to create black precipitate in clear liquid
• What is this copper compound I made?
• Is the salt of a weak acid and a weak base also a weak electrolyte?
• is there any difference between glycerin and glycerol?
• Can reactions produce microwave or radio wave radiation?
• What is the definition of organic compounds?
  • Difference between organic and inorganic chemistry
  • How can a thermometer ever show the actual temperature of an object if the object loses heat to the thermometer?
• How can I properly calculate the isoelectric point (pI) of amino acids?
• How does ammonium nitrate explode on its own?
• Can aluminium form blue-colored solution in liquid ammonia?
• What are the correct equilibrium arrows?
• physical chemistry - Can carbon dioxide be reduced to carbon monoxide and oxygen to produce energy?
• everyday chemistry - Are food calorie values really integers?
• experimental chemistry - How to differentiate between iron and sodium flames?
• organic chemistry - What is the name origin of ester?
• phase - At what pressure will hydrogen start to liquefy at room temperature?
• Why does pH affect fermentation?
• inorganic chemistry - How to extract pure potassium carbonate from ash?
• molecular structure - how to obtain potential curves from database?
• inorganic chemistry - Why does the solubility of Group II hydroxides increase and the solubility of sulphates decrease down the group?
• bond - Is melting/boiling point of ionically bonded substance higher than of covalently bound?
• terminology - What is the intuition behind ‘mol’ as a unit ‘symbol’
• inorganic chemistry - What is the equation for the reduction of water?
• thermodynamics - Work done on a Gas?
• terminology - Can precipitation occur in states of matter other than liquids?
• inorganic chemistry - Explanation for a basic decomposition of water experiment
• physical chemistry - Why is a third body needed in the recombination of two hydrogen atoms?
• How many electric vehicles can our current supply of lithium power?
• Cleaning with vinegar and sodium bicarbonate
• What has been the accepted value for the Avogadro constant in the “CRC Handbook of Chemistry and Physics” over the years?
• Why does entropy increase in reactions that make more molecules?
• Why do electrons jump back after absorbing energy and moving to a higher energy level?
• hydrocarbons - What is the carbon content, by weight, of vegetable oil?
• aqueous solution - leaving a spoon in a cup of tap water for about 12 hours makes a pattern of bubbles, why?
• thermodynamics - What would be the physical interpretation of the equation dG = Vdp − SdT?
• acid base - What pH value of 1M sodium crotonate solution supposed to be?
• How is it determined how many electrons are transferred in redox reactions?
• What happens inside salt bridges?
• Balancing reaction between copper and nitric acid given the ratio of formed nitrogen oxides
• Why do sulfur and oxygen form sulfur dioxide?
• organic chemistry - Why hydrogen bonding in some acids make them a stronger acid when it is present even before deprotonation?
• physical chemistry - Is the origin of non-integral atomic masses the difference in masses of the proton and neutron?
• physical chemistry - Can the equilbrium constant ever be exactly 1?
• reaction mechanism - How exactly does UV light break bonds?
• inorganic chemistry - Does ammonia exhibit hydrogen bonding in its gaseous state?
• Why are protons more common than hydride ion?
• How much CO2 is produced when burning 1GJ of Natural Gas
• Peak in beer freezing temperature plot
• distillation - Does distilled water still have ions in it? Does deionized water lack ions, but still have other “stuff” in it?
• nomenclature - Why use “molecular equation” to refer to a chemical equation describing a precipitation reaction?
• organic chemistry - How can I tell whether or not a molecule is planar?
• How does H2SO4 dissociate?
• chemical formula - Combustion analysis of hydrocarbon
• Why are almost all fruits acidic?
• Why is carbonic acid often ignored?
• inorganic chemistry - Why do diluted sulfuric acid and hydrogen peroxide etch copper only when chloride ions are present?
• Where does the energy from combustion come from?
• electronic configuration - Reasoning for why anions have larger radius
• physical chemistry - Why is supersaturated sodium acetate so (meta)stable?
• What is the origin of the word salt as used in chemistry?
• Molar conductivity calculation in a titration curve
• How should you report measurements and uncertainty for a measuring cylinder with 0.5 mL graduations?
• nomenclature - Are there separate quantity symbols for the pKa of a substance and the pKa of its conjugate acid?
• solutions - Name of particles in a suspension
• physical chemistry - Why does aluminum have a lower first ionization energy than magnesium?
• aqueous solution - How to convert from w/w% to molarity?
• thermodynamics - Prigogine vs. Bronsted and the minimum entropy production principle
• physical chemistry - How do thermodynamic variables behave in reversible and irreversible processes?
• Why do sp³ orbitals have tetrahedral symmetry when they are linear combinations of orbitals with octahedral symmetry?
• What is the difference between the KLMN and SPDF methods of finding electronic configuration?
• Why is there a decrease in the total volume when NaOH dissolves in water?
• acid base - Is it appropriate to call an element an amphoteric substance?
• physical chemistry - Equilibrium Bond Length & Diatomic Molecules
• analytical chemistry - Difference between a “cartoon” flame test and a “real” flame test? How do chemists do flame tests correctly?
• acid base - Why doesn’t hydroxide associate with water analogously to proton forming hydronium?
• inorganic chemistry - Equilibrium constant for isothermal double equilibrium “shift”
• What happens when you add a weak acid to a solution buffered at a pH of 8.0?
• stoichiometry - Does stoichiometric gas mixture produce the highest explosion pressure (or energy) compared with other explosive limit mixture?
• acid base - How do you explain pKa to non-professional?
• How come nuclear waste is so radioactive when uranium is relatively stable with an extremely long half life?
• Solubility of oxygen in water with temperature, why does the change in solubility decrease around 40 °C?
• …

Autres sites de questions et réponses

• https://socratic.org/chemistry (licence CC-BY-NC-SA)
• https://www.quora.com/topic/Chemistry
• Reddit Chemistry
• Reddit Science Education
• For .gifs that provide knowledge!
• …

Questions diverses

• Ça sent le gaz, mais pourquoi le gaz sent? Michel Alberganti — 22 janvier 2013
• Can Gibbs energy of formation be calculated from enthalpy and entropy?