Transcript Document
Honors General Chemistry 1050 [03] Chapter 1. Review of General Knowledge Chemistry is the study of matter and its properties, the changes that matter undergoes, and the energy associates with those changes. (at the levels of sub-molecule, molecule, and molecular ensemble) Matter is the physically observable object, which is ubiquitously differentiable according to its compositions. Composition: Two Forms Pure substances: formed of one type of molecule well-defined physical and chemical properties Mixture: formed of multiple types of molecules physical and chemical properties are dependent on the specific composition (type and amount). Some key phenomena for pure substances do not exist. for instance: melting point in rubber ? How about Plastic ? Property and Change Physical Change: any non-molecular-composition change (atom rearrangement). = change of physical property (how the matter can be changed, when molecule is not changed) Melting, Boiling, Color change, Density change, friction Change… Chemical Change: any change of molecular composition = change of chemical property (how molecule can be changed) “Reaction”, Salt Solvation, Corrosion Property and Change The same substance can have different “Physical Properties” and “Chemical Properties”. The different substance must have different “Physical Properties” and “Chemical Properties”. Chemical Change is always associated with Physical Change. What may be associated with Changes ? “Composition, Structure and Energy …” Energy is the only driving force for changes. Potential Energy is the stored energy: Gravitational energy, Elastic energy, and Chemical energy… Kinetic Energy is the energy, “stored” in the motion. Chemistry is the science on how energies flow with all the possible changes at the level of molecule, submolecule and molecular Ensemble. How to compare the properties: Measurements. The common references are essential for measurements (UNIT) Fundamental Units and Derived Units Length Measure quantity: Time Speed=Length/Time 6m 2s 3 m/s Number: 6 2 3 Unit: m s m/s Some unit is well-defined: J = mmm/s/s Conversion Factors in Calculations Varieties of units: sizes of often measured subjects & history Commonly used units: dependent on often measured subjects. Uncertainty and Significant Figures There is no absolute certain measurement. Different measurement apparatus have varied precisions. Two things need to be remembered on scientific measurement: 1. Uncertainty can not be avoided (random error); 2. Mistake should be avoided (systematic error). 30.56 ± 0.01 kg, 57.8 ± 0.1 s Uncertainty and Significant Figures How to record the values of measured quantities ? 1. 30.56 ± 0.01 kg, 57.8 ± 0.1 s 1. 30.56 30.5 read directly from balance 0.06 estimate the rightmost digit from balance “30.56 has four significant figures.” How to count significant figures ? All the numbers are significant except zeros that are not measured but are used to position the decimal point. Uncertainty and Significant Figures 0.009680 s, 4 sf 8.1 10-4 m, 80. K, 80.00 K 2 sf 2 sf 4 sf Uncertainty and Significant Figures Rules for Rounding off: 1. If the digit removed is more than 5, the preceding number is increased by 1; 2. If the digit removed is less than 5, the preceding number is unchanged; 3. If the digit removed is 5, the preceding number is increased by 1 if it is odd and remains unchanged if it is even.