think about what you had for breakfast today. the packaging on any processed food you ate, including cereal, milk,bread and yogurt, has a label that provides you with nutrition information so you can make healthy diet choice. this imformation comes from chemical analysis.
suppose you ate a boiled egg and a banana instead of the cereal and milk. there is no label with nutrition information there, but analytical chemists have rested a sample of eggs and bananas for residues of harmful chemicals so you can be confident that your breakfast is safe to eat.
your toothpaste, too, will have a label that says something like 'active ingredient 0.7% w/w sodium monofluorophosphate'. an analytical chemist would have checked that this amount of active ingredient was correct.
analytical chemists are employed in a range of industries, from food manufacturing to environmental monitoring and foerensic sciences and many more. they use a range of techniques and technologies to determine the identity, quality, and quantity of the chemicals that make up our world.
the composition of consumer goods is of great importance. for example, residues such as dieldrin and DDT have been detected in meat. nutrionists urge us to eat fish on a regular basis to take advantage of the beneficial fatty scids that many fish contain. but fish can also contain heavy metals, such as mercury. goernments have placed restrictions on the amount of pesticides and heavy metals allowed in foods. for example, the acceptable daily intake of DDT is 0.002 milligram per kilogram of body weight per day(0.002mg/kg/day) while that of dieldrin is 0.0001mg/kg/day

是物理和化学还是物化？如果是物理和化学，那么还是高考卷子历年的比较好如果是大学的物化，那么还是看你们要考哪一版的，然后题就做对应的习题，我们学的是第三版的，也就是下面有人说的那个一版，然后做题可以选择大红本，或是第三版，或是第六版的题，这个针对性比较广

w>0,系统得到环境所做的供；w<0时，环境得到系统所作的功，即系统对环境作功（见教材40页）
这教材是天津大学物理化学教研室编的，王正烈，周亚平修订，高教出版社出版的。我是理工的学生，现在我们的教材用的是这一版。
希望能对你有所帮助