Class02 - Chemistry 83 Science of Chemistry Science is...

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Chemistry 83 Class02 1 Science of Chemistry Science is knowledge obtained by making, organizing, and explaining observations Joesten,”Essentials”,Saunders, 1993, 3 Chemistry is a discipline of natural science, which is concerned with knowledge about matter (anything that occupies space and has mass) and energy (that which is able to cause motion of matter) Study of Non-living Matter
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Chemistry 83 Class02 2 Chemistry Composition of matter Structure of matter Properties of matter Changes that matter undergoes and the associated energies Contents of the discipline of chemistry Organize observations Explain observations Composition of Matter - description of components of samples and how they are combined Compound ( Combination of elements in fixed ratios shown as subscripts in formulas : H 2 O, NaCl) Element ( Simplest substance - represented by symbols : H, O, Na, Cl) Pure Substance (Fixed composition and homogeneous) Mixture (Variable composition - combination of elements and/or compounds) Homogeneous ( Uniform: solution of NaCl in H 2 O) Heterogeneous ( Non-uniform: NaCl and pepper)
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Chemistry 83 Class02 3 Physical Properties (observation does not require a change in composition) Chemical Properties (observation requires change in composition) Properties of Matter - identifying characteristics Melting point Boiling point Density Color Odor Reacts with water Reacts with oxygen Inert Explosive Flammable Physical Changes (involve no change in composition) Chemical Changes (involve change in composition) Changes in Matter Melting, boiling, etc. Burning, decomposing, etc. These changes in matter are always accompanied by changes in energy with physical changes involving less energy than chemical changes
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Chemistry 83 Class02 4 http://www.grc.nasa.gov/WWW/K-12/airplane/state.html cool heat cool heat Changes in states of matter require changes in energy Stoker, H.S., Chemical Principles, 3rd, MacMillan, NY, 1990 Endergonic Changes - energy is required continuously. Called endothermic if energy is heat.
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