Thermochemical equation is a compact equation representing a chemical reaction that describes both the stoichiometry and the energetics of the reaction. For example, the thermochemical equation
means When one mole of gaseous methane is burned in two moles of oxygen gas, one mole of carbon dioxide gas and 2 moles of steam are produced, and 2 220 kJ of heat are released.
Van der Waals’ equation is an equation of state for real fluids which takes the form:
where p is pressure, Vm is molar volume, T is temperature, R is the molar gas constant, and a and b are characteristic parameters of the substance which describe the effect of attractive and repulsive intermolecular forces.
Van’t Hoff equation is the equation expressing the temperature dependence on the equilibrium constant K of a chemical reaction:
where ΔrH° is the standard enthalpy of reaction, R the molar gas constant, and T the temperature.
The Heyrovsky-Ilkovic equation describes the entire current-potential curve (polarographic wave) of a reversible redox system in polarography
where R is the gas constant, T is the absolute temperature, F is the Faraday constant, n denotes the number of electrons taking part in the electrode reaction. E1/2 is a unique potential (for a given reaction and supporting electrolyte) termed the half-wave potential.
In order to obtain E1/2 from the above equation, we plot a graph of ln[(id-i)/i] against E. The intercept on the x-axis gives then an accurate value of E1/2. The slope of the obtained straight line is equal to nF/RT from which n is determined.
Schrötter decomposition apparatus (Schrötter's alkalimeter) is used to determining the carbonate content in samples of limestone, gypsum, dolomite, or baking powder by loss of weight. The apparatus is named after the Austrian chemist Anton Schrötter von Kristelli (1802-1875), who devised it in 1871. The size of the filled apparatus (apparatus is 16 cm high) is such that it weights less than 75 g, and can be placed on the pan of an analytical balance.
Procedure: Weigh about 0.5 g of the powdered carbonate sample and introduce it into the decomposition flask C. Pour into the drying tube A 2-3 mL of concentrated sulphuric acid (H2SO4), and to the dropping funnel B add about 10-15 mL of hydrochloric acid (w(HCl) = 15 %). Weigh the whole apparatus. Open the upper taps of both parts and allow the hydrochloric acid from B to run slowly down on to the powdered sample. The evolved CO2 escapes through the strong sulphuric acid and is thus thoroughly dried. When further addition of acid produces no more evolution of CO2, warm the apparatus up to 80 °C so as to expel the CO2 from the solution. Connect the upper tap of the drying tube A to a water pump and draw a slow current of air through the apparatus until completely cool. Open the upper taps for a moment to equalize the internal and external pressure and weight the apparatus again. The weight loss is equal to the weight of carbon dioxide liberated from the carbonates.
In 1889, Svante Arrhenius explained the variation of rate constants with temperature for several elementary reactions using the relationship
where the rate constant k is the total frequency of collisions between reaction molecules A times the fraction of collisions exp(-Ea/RT) that have an energy that exceeds a threshold activation energy Ea at a temperature of T (in kelvin). R is the universal gas constant.
Acetals are organic compounds having the structure R2C(OR’)2 (R’ ≠ H). They are organic compounds formed by addition of alcohol molecules to aldehyde or ketone molecules. Originally, the term was confined to derivatives of aldehydes (one R = H), but it now applies equally to derivatives of ketones (neither R = H ). Mixed acetals have different R’ groups. The formation of acetals is reversible; acetals can be hydrolysed back to aldehydes (ketone) in acidic solutions.
Acetal, 1,1-diethoxyethane (CH3CH(OC2H5)2), is an organic compound, pleasant smelling, formed by addition of ethyl alcohol to ethanal (acetaldehyde). It is used as a solvent and in synthetic organic chemistry.
Ampere (A) is the SI base unit of electric current.
The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2×10-7 newton per metre of length.
AMU or atomic mass unit is a unit of mass used to express relative atomic masses. It is equal to 1/12 of the mass of an atom of the isotope carbon-12 and is equal to 1.66 033×10-27 kg. This unit superseded both the physical and a chemical mass unit based on oxygen-16 and is sometimes called the unified mass unit or the dalton.
Generalic, Eni. "Equal-arm balance." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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