Magnesium heat capacity

Brunauer and co-workers [129, 130] found values of of 1310, 1180, and 386 ergs/cm for CaO, Ca(OH)2 and tobermorite (a calcium silicate hydrate). Jura and Garland [131] reported a value of 1040 ergs/cm for magnesium oxide. Patterson and coworkers [132] used fractionated sodium chloride particles prepared by a volatilization method to find that the surface contribution to the low-temperature heat capacity varied approximately in proportion to the area determined by gas adsorption. Questions of equilibrium arise in these and adsorption studies on finely divided surfaces as discussed in Section X-3. 

P4.1 Given the following heat capacity information for magnesium metal as a function of temperature... 

The sp-valent metals such as sodium, magnesium and aluminium constitute the simplest form of condensed matter. They are archetypal of the textbook metallic bond in which the outer shell of electrons form a gas of free particles that are only very weakly perturbed by the underlying ionic lattice. The classical free-electron gas model of Drude accounted very well for the electrical and thermal conductivities of metals, linking their ratio in the very simple form of the Wiedemann-Franz law. However, we shall now see that a proper quantum mechanical treatment is required in order to explain not only the binding properties of a free-electron gas at zero temperature but also the observed linear temperature dependence of its heat capacity. According to classical mechanics the heat capacity should be temperature-independent, taking the constant value of kB per free particle. 

References relative to the monomer-dimer ratio in magnesium chloride vapor are given in the discussion for monomeric ideal gas. The selected best value for the enthalpy of dimerization at 900 K is -39.2 kcal mol". Combined with enthalpy of formation data for the monomer and the heat capacity of the dimer, this yields A H (298.15 K) - -228.10 kcal mol". ... 

Craig et al. (1 ) measured the heat capacity in the region 12-320 K. Only smoothed values at 10 K intervals were reported and these were based on an Incorrect relative atomic mass. Furukawa et al. ( ) stated that the heat capacity values should be multiplied by 24.32/24.22 = 1.0041 to be consistent with the atomic mass of 1954. The current value for the relative atomic mass of magnesium requires a multiplier of 24.305/24.22 1.0035. Our analysis of this smoothed data (with orthogonal polynomials) suggests that the reported values at 18 K and 200 K may be In error. 

Problem The heat capacity at 1 atm. pressure of solid magnesium, in the temperature range from 0° to 560 C, is given by the expression... 

A strip of magnesium metal having a mass of 1.22 g dissolves in 100. mL of 6.02 M HCl, which has a specific gravity of 1.10. The hydrochloric acid is initially at 23.0°C, and the resulting solution reaches a final temperature of 45.5°C. The heat capacity of the calorimeter in which the reaction occurs is 562 J/°C. Calculate AH for the reaction under the conditions of the experiment, assuming the specific heat of the final solution is the same as that for water, 4.18 J/g °C. 

Similarly, Holm et al. (1973) measured the enthalpy increments Hr — 7/298 of the congmently melting compounds of 2 1 and 1 1 alkali metal chlorides and magnesium chloride using a high-precision adiabatic drop calorimeter. From the results obtained at several experimental temperatures corresponding with solid and liquid samples, they determined the enthalpies of fusion of these compounds. Values for heat capacities for the molten salt mixtures were also derived. The heat capacities for the 2 1 and 1 1 compounds were estimated from those of the binary compounds according to the relation... 

A 0.1375-g sample of solid magnesium is burned in a constant-volume bomb calorimeter that has a heat capacity of 1769 J/°C. The calorimeter contains exactly 300 g of water, and the temperature increases by 1.126°C. Calculate the heat given off by the burning Mg, in kJ/g and in kJ/mol. 

The energy required to raise the temperature of the hydroxide solids from ambient temperature (298 K) to the temperature of decomposition, 350°C (623 K) can be calculated using the specific heat capacity of magnesium hydroxide at 600 K (1.78 kJ/kg K) as follows ... 

VIC/D0U] Victor, A. C., Douglas, T. B., Physical properties of high temperature materials. Part VI. Enthalpy and heat capacity of magnesium oxide, zirconium oxide, and zirconium silicate from 0 to 900°C, Natl.Bur. Stand., Annu. Rep.fU.S.), (1961). Cited on pages 217,218. 

Magnesium hydroxide functions in a manner similar to ATH. It liberates water from crystallization in a fire situation and in so doing it forms a barrier to the ingress of oxygen required for combustion. The material is also capable of absorbing heat, although the heat capacity value of 77.0 J/K mol (crystalline) is lower than that for ATH. 

High-temperature The predominant industrial application of magnesium compounds is in the use of thermal insulation magnesite and dolomite in refractory bricks. Bricks of high-purity magnesia are (2%) exceptionally wear and temperature resistant, with high heat capacity and... 

As an example, with such equipment, Kaschnitz et td. (2005) could measure the heat capacity and other thermophysical quantities of a magnesium ahoy in the temperature region of 570-850 K with an uncertainty of 5%. 

Gmelin, E. (1967) A cryostat for measuring heat capacities from 1.2 to 300° K and measurements of the specific heat of magnesium oxide below 36° K. Cryogenics, 7, 225-232. 

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