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Factors that affect specific heat capacityDegrees of freedom: Molecules are quite different from the monatomic gases like helium and argon. With monatomic gases, heat energy comprises only translational motions. Translational motions are ordinary, whole-body movements in 3D space whereby particles move about and exchange energy in collisions (like rubber balls in a vigorously shaken container). These simple movements in the three X, Y, and Z–axis dimensions of space means monatomic atoms have three translational degrees of freedom. Molecules, however, have various internal vibrational and rotational degrees of freedom because they are complex objects; they are a population of atoms that can move about within a molecule in different ways (see animation at right). Heat energy is stored in these internal motions. For instance, nitrogen, which is a diatomic molecule, has five active degrees of freedom: the three comprising translational motion plus two rotational degrees of freedom internally. Not surprisingly, nitrogen has five-thirds the constant-volume molar heat capacity as do the monatomic gases. See Thermodynamic temperature for more information on translational motions, kinetic (heat) energy, and their relationship to temperature.Molar mass: When the specific heat capacity, c, of a material is measured (lowercase c means the unit quantity is in terms of mass), different values arise because different substances have different molar masses (essentially, the weight of the individual atoms or molecules). Heat energy arises, in part, due to the number of atoms or molecules that are vibrating. If a substance has a lighter molar mass, then each gram of it has more atoms or molecules available to store heat energy. This is why hydrogen—the lightest substance there is—has such a high specific heat capacity on a gram basis; one gram of it contains a relatively great many molecules. If specific heat capacity is measured on a molar basis (uppercase C), the differences between substances is less pronounced and hydrogen’s molar heat capacity is quite unremarkable. Conversely, for molecular-based substances (which also absorb heat into their internal degrees of freedom), massive, complex molecules with high atomic count — like gasoline — can store a great deal of energy per mole and yet, be quite unremarkable on a mass basisSince the bulk density of a solid chemical element is strongly related to its molar mass, generally speaking, there is a strong, inverse correlation between a solid’s density and its cp (constant-pressure specific heat capacity on a mass basis). Large ingots of low-density solids tend to absorb more heat energy than a small, dense ingot of the same mass because the former comprises more atoms. Thus, generally speaking, there a close correlation between the size of a solid chemical element and its total heat capacity (see Volumetric heat capacity). There are however, many departures from the general trend. For instance, arsenic, which is only 14.5% less dense than antimony, has nearly 59% more specific heat capacity on a mass basis. In other words; even though an ingot of arsenic is only about 17% larger than an antimony one of the same mass, it absorbs about 59% more heat energy for a given temperature rise.Hydrogen bonds: Hydrogen-containing polar molecules like ethanol, ammonia, and water have powerful, intermolecular hydrogen bonds when in their liquid phase. These bonds provide yet another place where kinetic (heat) energy is stored.Substance Phase cp Cp Cv J g-1 K-1 J mol-1 K-1 J mol-1 K-1Air (Sea level, dry, 0 °C) gas 1.0035 29.07Air (typical room conditions) gas 1.012 29.19Aluminium solid 0.897 24.2Ammonia liquid 4.700 80.08Antimony solid 0.207 25.2Argon gas 0.5203 20.7862 12.4717Arsenic solid 0.328 24.6Beryllium solid 1.82 16.4Copper solid 0.385 24.47Diamond solid 0.5091 6.115Ethanol liquid 2.44 112Gasoline liquid 2.22 228Gold solid 0.1291 25.42Graphite solid 0.710 8.53Helium gas 5.1932 20.7862 12.4717Hydrogen gas 14.30 28.82Iron solid 0.450 25.1Lead solid 0.127 26.4Lithium solid 3.58 24.8Magnesium solid 1.02 24.9Mercury liquid 0.1395 27.98Nitrogen gas 1.040 29.12 20.8Neon gas 1.0301 20.7862 12.4717Oxygen gas 0.918 29.38Silica (fused) solid 0.703 42.2Uranium solid 0.116 27.7Water gas (100 °C) 2.080 37.47 28.03 liquid (25 °C) 4.1813 75.327 74.53 solid (0 °C) 2.114 38.09All measurements are at 25 °C unless otherwise noted.Notable minima and maxima are shown in maroon.
I'm expecting a harsh winter, and want to make a decent hand-warmer 
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Water is by far the material with the highest thermal capacity no other solid or liquid comes near.
Although water is a very good heat storage materiel surely the best way to store heat is by means of a liquid to solid phase change.Again water is very good but it occurs at the inconveniently low temperature of 0°C, what we need is some materiel where this phase change occurs in the 30-50°C region, any suggestions?.My great grandmother (born 1855) used to recommend a quantity of decayed wood (touch wood) smouldering in a tin can.