Science Explanations
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Qu. 1. Density can be used to identify a substance. It could be used to determine if a sample of gold-colored metal is, in fact, gold. Archimedes used the concept of density to identify substances (Day, 2004). Density is a physical property of a substance which describes the degree of compactness of the substance, i.e. how close together the atoms are packed. The density of a substance is the ratio of an object's mass to its volume: density = mass/volume, and is measured in grams per cubic centimeter, or grams per milliliter. The density of a substance changes with temperature, i.e. as substances are heated, they expand and their density decreases. This explains how hot air balloons work: as the air within the balloon is heated, it expands, and becomes less dense than the air outside the balloon, causing the balloon to rise.Qu. 2. Matter exists in three different forms: as a solid, a liquid, or a gas. In the solid state, the molecules of the matter are packed closely together, and the forces of attraction between the molecules overcome the forces of translational motion, so they do not move around (States, 2003). However, the do exhibit vibrational motion in the solid state. In the liquid state, the molecules are still closely packed, but not as closely packed as in the solid state, so they can move around. They do not have enough energy to leave the liquid state and become a gas under normal circumstances, except for a few fast-moving molecules which escape t
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pressure increases (Sisler, VanderWerf and Davidson, 1967, 58). The quantity of heat required to vaporize a unit weight of a given liquid is called its heat of vaporization. It decreases with increases in temperature. Evaporation and vaporization involve a loss of energy by the liquid: as the faster, high-energy molecules escape, only the slower, low-energy ones are left behind, and so the liquid is cooled. Heat must be continually applied to keep the temperature constant.
Qu. 3. An English chemist named John Dalton is considered the "father" of modern atomic theory (Development, 2004). Dalton had four basic ideas on atomic theory: chemical elements are made up of atoms; the atoms of an element are identical in their masses; atoms of different elements have different masses; and atoms only combine in small, whole number ratios such as 1:1, 1:2, 2:3, etc. (Park, 2000). That elements are made up of atoms is still true, and has been known since the time of the Ancient Greeks. The second, idea, that all atoms of an element are identical has since been disproved, but the idea of isotopes was unknown in Dalton's time (1766-1844).
The third idea, that atoms of different elements have different masses, was not new, but D
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Approximate Word count = 3823
Approximate Pages = 15 (250 words per page)
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