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Thematic studies

Done by: Wong Wei Cong (32) 1A1. Thematic studies. Units and Measurements; Kinetic Particles Theory; Elements, Compounds and Mixtures. Kelvin V.S. Celsius Mass V.S. Weight Old units– Foot Diffusion Why does ice float on water? Alloy Allotropes. Contents. International System of Units

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Thematic studies

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  1. Done by: Wong Wei Cong (32) 1A1 Thematic studies Units and Measurements; Kinetic Particles Theory; Elements, Compounds and Mixtures

  2. Kelvin V.S. Celsius Mass V.S. Weight Old units– Foot Diffusion Why does ice float on water? Alloy Allotropes Contents

  3. International System of Units -- SI Units Introduction In 1968, French scientists came up with the seven base quantities (length, mass, time, electric current, temperature, light intensity and amount of substance) and their International System of Units or SI units (meter, kilogram, second, ampere, Kelvin, candela and mole respectively).

  4. Kelvin V.S. Celsius Celsius is a temperature scale that is named after the Swedish astronomer Anders Celsius. The magnitude of degree Celsius is precisely equal to that of kelvin. The Kelvin scale is a thermodynamic temperature scale with reference to absolute zero, the point where matter exhibits zero entropy theoretically. The secondary reference point on the Kelvin scale is the triple point of water, i.e. 0.01 degree Celsius. The Kelvin scale is the difference between these two reference points, with the kelvin defined as 1/273.16 of this scale. The Kelvin scale and the kelvin are named after the Scottish physicist and engineer William Thomson, 1st Baron Kelvin. The kelvin is often used in the measure of the color temperature of light sources. Color temperature is based upon the principle that a black body radiator emits light whose color depends on the temperature of the radiator. Black bodies with temperatures below about 4000 K appear reddish whereas those above about 7500 K appear bluish. In electronics, the kelvin is used as an indicator of how noisy a circuit is in relation to an ultimate noise floor, i.e. the noise temperature.

  5. In physics, the weight of an object is the magnitude of the force that must be applied to an object in order to support it in a gravitational field. The weight of an object in static equilibrium equals the magnitude of the gravity acting on the object. Near the surface of the Earth, the acceleration due to gravity is approximately constant, i.e. 9.80665 m/s.Mass is an intrinsic property of matter, whereas weight is a force that results from the action of gravity on matter. Weight measures how strongly gravity pulls on that matter, but mass is the amount of matter in an object. Mass remains the same anywhere, while weight changes in different gravitational fields. Mass V.S. Weight

  6. Old Units-- Foot The foot is a traditional unit of distance. Almost every culture has used the human foot as a unit of measurement. The natural foot, an ancient unit based on the length of actual feet, is about 25 centimetres. This unit was replaced in early civilizations of the Middle East by a longer foot, which is about 30 centimetres, because this longer length was conveniently expressed in terms of other natural units: 1 foot = 3 hands = 4 palms = 12 inches (thumb widths) = 16 digits (finger widths)The modern foot, which is about 30.5 centimetres, may be an innovation of Henry I, who reigned from 1100 to 1135. The foot belongs to the English or Imperial system, which is linked through a network of international agreements supporting the International System of Units. A foot is equal to 0.3048 meters. The SI units are based on stable properties of the Universe. The meter is defined by stating that the speed of light, a universal physical constant, is exactly 299 792 458 meters per second. The English units are more cumbersome to use than metric units in trade and in science because of their many eccentricities.

  7. Conclusion The importance of units is not to be underestimated. Kinetic Particle Theory Introduction A picometre (symbol pm) is a unit of length in the metric system, equal to one trillionth, i.e. (1/1,000,000,000,000) of a metre, which is the current SI base unit of length. Do you that a helium particle has an estimated radius of 31 picometres? How do the particles move?

  8. Why does ice float on water? Water reaches its maximum density at 4°C (40°F). As it cools further and freezes into ice, it actually becomes less dense. On the other hand, most substances are most dense in their solid (frozen) state than in their liquid state. Water is different because of hydrogen bonding. A water molecule is made from one oxygen atom and two hydrogen atoms, strongly joined to each other with covalent bonds. Water molecules are also attracted to each other by weaker chemical bonds (hydrogen bonds) between the positively-charged hydrogen atoms and the negatively-charged oxygen atoms of neighboring water molecules. As water cools below 4°C, the hydrogen bonds adjust to hold the negatively charged oxygen atoms apart. This produces a crystal lattice, known as ‘ice’. Ice floats because it is about 9% less dense than liquid water. The heavier water displaces the lighter ice, so ice floats to the top. One consequence of this is that lakes and rivers freeze from top to bottom, allowing fish to survive even when the surface of a lake has frozen over. If ice sank, the water would be displaced to the top and exposed to the colder temperature, forcing rivers and lakes to fill with ice and freeze solid.

  9. diffusion Diffusionrefers to the spontaneous movement of a substanceinto its surrounding area. The particles that make up the substance distribute over time from an area of higher concentration to an area of lower concentration in order to create, at equilibrium, a uniform distribution of particles throughout the system. Diffusion is a natural process that requires no added energy to occur. It increases the entropy of the system and hence is an energetically favourable and irreversible process.

  10. An example of diffusion is the release of a drop of ink into a beaker of water. The ink will be visibly distinguishable from the water for some amount of time, but it will diffuse eventually to all areas of the beaker. The collision of the ink molecules with the water molecules keeps diffusion from happening quickly. This is an example of a liquid diffusing into another liquid. In comparison to a liquid, a gas has a much lower density. With fewer molecules with which to collide, diffusion of gases occurs much more quickly than diffusion of liquids or solids. Comparing two gases, the lighter gasdiffuses faster that the heavier.Solids diffuse into one another as well, but at an even slower rate than liquids. The molecules in a solid cannot move very much at all. Not only does a solid have greater density compared to a liquid or gas, resulting in the very short movement of one molecule before its collision with another, but energetically favourable intermolecular interactions of a solid also slow diffusion. As a result, diffusion of a solid into another solid takes place over a very long period of time.

  11. Common examples of diffusion include the diffusion of solids into liquids, such as salt into water. The formation of a solution of the salt in the water by this process is called dissolution. A liquid may diffuse into a gas by the process of evaporation, or a solid into a gas by the process of sublimation.Osmosis is the diffusion of a liquid across a semipermeable membrane. Osmosis is important in the extraction by plants of water from the soil. Dialysis is an important application of diffusion. In dialysis a solution is passed over a semipermeable membrane, allowing solutes up to a certain size to diffuse across the membrane to a second solution. Artificial kidney machines use dialysis to remove metabolic waste products, such as urea and creatinine, from the blood. In these machines, blood is circulated on one side of a semipermeable membrane made from cellophane, while a dialysis fluid, which closely matches the chemical composition of blood, is circulated on the other side of the membrane. The waste products diffuse from the blood into the dialysis fluid and are then discarded. Important blood components, such as the oxygen- carrying protein hemoglobin, are too large to enter the pores of the membrane and hence are retained in the blood.

  12. A final example of the biological importance of diffusion is the exchange of gases to and from the blood that occurs in the alveolar membrane of the lungs. This membrane separates the flowing blood from the gases within the lung. Carbon dioxide is plentiful in venous blood that enters the lung. Release of the CO2 from this blood occurs by its diffusion across the alveolar membrane, and this CO2 is expelled upon exhalation. Inhalation brings air into the lung, and air contains 20.95% by volume of oxygen. Diffusion of O2 across the alveolar membrane, in the other direction, allows its dissolution in the blood. Oxygen is carried, bound to hemoglobin, by the arterial blood to the cells where it is released--again by diffusion--for its use by the cells as the terminal oxidant of aerobic respiration.

  13. Conclusion Solids vibrate about their fixed positions, liquids roll or slide over one another and gases move randomly in all directions. Elements, Compounds and Mixtures Introduction After learning how particles move, what exactly are the particles?

  14. Alloy An alloy is a partial or complete solid solution of one or more elements in a metallic matrix. Alloying one metal with other metal(s) or non metal(s) often enhances its properties. For example, steel is stronger than iron. The physical properties, such as density, reactivity, and electrical and thermal conductivity, of an alloy may not differ greatly from those of its elements, but engineering properties, such as tensile strength and shear strength may be substantially different from those of the constituent materials. This is sometimes due to the sizes of the atoms in the alloy, since larger atoms exert a compressive force on neighboring atoms, and smaller atoms exert a tensile force on their neighbors, helping the alloy resist deformation. Some alloys are made by melting and mixing two or more metals. Bronze, an alloy of copper and tin, was the first alloy discovered, during the prehistoric period now known as the Bronze Age; it was harder than pure copper and originally used to make tools and weapons, but was later superseded by metals and alloys with better properties. In later times bronze has been used for ornaments, bells, statues, and bearings. Brass is an alloy made from copper and zinc.

  15. Allotropes Allotropy is a behavior exhibited by some chemical elements: these elements can exist in two or more different forms, known as allotropes of that element. In each allotrope, the element's atoms are bonded together in a different manner. Allotropes are different structural modifications of an element. For example, carbon has 3 common allotropes: diamond, where the carbon atoms are bonded together in a tetrahedral lattice arrangement, graphite, where the carbon atoms are bonded together in sheets of a hexagonal lattice, and fullerenes, where the carbon atoms are bonded together in spherical, tubular, or ellipsoidal formations. For some elements, allotropes have different molecular formulae which can persist in different phases – for example, two allotropes of oxygen (dioxygen, O2 and ozone, O3), can both exist in the solid, liquid and gaseous states. Conversely, some elements do not maintain distinct allotropes in different phases – for example phosphorus has numerous solid allotropes, which all revert to the same P4 form when melted to the liquid state.

  16. Conclusion An element is the simplest kind of matter which cannot be broken down into two or more simpler substances. A compound is a substance containing two or more elements chemically combined together. . A mixture is a substance containing two or more elements not chemically combined together.

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