Composite materials such as wood and high-density polyurethane foam contain void spaces which reduce the average density. Metals, whose atoms pack together quite compactly, have the highest densities, although that of lithium, the highest metallic element, is quite low. The density range of solids is quite wide. Liquid densities are largely independent of pressure, but they are somewhat temperature-sensitive. Mercury, being a liquid metal, is something of an outlier. Liquids encompass an intermediate range of densities. For example, in the plagioclase series, the density increases as sodium (albite, 2.61 g/cm 3) is replaced by calcium (anorthite, 2.75 g/cm 3 ). Measurement of the density of a gas is a simple experimental way of estimating its molecular weight. The density will change systematically as composition varies. To the extent that a gas exhibits ideal behavior (low pressure, high temperature), the density of a gas is directly proportional to the masses of its component atoms, and thus to its molecular weight. In general, gases have the lowest densities, but these densities are highly dependent on the pressure and temperature which must always be specified. What we conventionally call the "density" is more precisely known as the "mass density".ĭensity can be expressed in any combination of mass and volume units the most commonly seen units are grams per mL (g mL –1, g cm –3), or kilograms per liter. The general meaning of density is the amount of anything per unit volume. The volume units milliliter (mL) and cubic centimeter (cm 3) are identical and are commonly used interchangeably. This quantity \(\rho\) is known as the density, which is usually defined as the mass per unit volume: Denoting mass and volume by \(m\) and \(V\) respectively, we can write the equation of each line as \(m = \rho V\), where the slope \(\rho\) (Greek lower-case rho) is the proportionality constant that relates mass to volume. The only difference between these plots is their slopes. the plots are all straight lines, which signify direct proportionality.the plots all have the same origin of (0,0): if the mass is zero, so is the volume.These plots show how the masses of three liquids vary with their volumes. It is this ratio, (mass ÷ volume), that we are concerned with in this Module. T he ratio of two extensive properties is always an intensive property - one that characterizes a particular kind of matter, independently of its size or mass. Mass and volume are measures of the quantity of a substance, and as such are defined as extensive properties of matter. But in making such statements, we are implicitly comparing equal volumes of these substances: after all, we know that a cup of sugar will weigh more than a single ordinary steel nail. Density The average density of a substance or object is defined as its mass per unit volume, m V m V where the Greek letter (rho) is the symbol for density, m is the mass, and V is the volume. Most of us have long understood that "oil is lighter than water", or that iron is "heavier" than sugar.
0 Comments
Leave a Reply. |