Fundamental Chemical Laws • Law of conserva<on of mass Mass is neither created nor destroyed Antoine Lavoisier There are three important fundamental laws that govern all chemistry Mass cannot be created/destroyed, although it may be rearranged in space, and changed into different types of particles. This implies that for any chemical process in a closed system, the mass of the reactants must equal the mass of the products. CH 4 + 2O 2 → CO 2 + 2H 2 O X g → X g
Example In a combustion reaction, 46.0 g of ethanol reacts with 96.0 g of oxygen to product water and carbon dioxide. If 54.0 g of water is produced, what mass of carbon dioxide is produced?
Fundamental Chemical Laws • Law of deFnite propor<on A given compound always contains exactly the same propor:on of elements by mass. Joseph Proust There are three important fundamental laws that govern all chemistry A chemical compound always contains exactly the same proportion of elements by mass. An equivalent statement is the law of constant composition , which states that all samples of a given chemical compound have the same elemental composition. Any amount of water (H 2 O) is composed of 8/9 O atoms and 1/9 H atoms regardless of the mss of the sample
Example A sample of chloroform (CHCl 3 ) is found to contain 12.0 g of carbon, 106.4 g of chlorine and 1.01 g of hydrogen. If a second sample of chloroform is found to have 30.0 g of carbon, what is the total mass of chloroform in the second sample?
Three samples of a solid substance composed of elements A and Z were prepared. The first contained 4.31 g of A and 7.70 g of Z. The second sample was 35.9% A and 64.1% Z. It was observed that 0.718 g of A reacted with Z to form 2.00 g of the third sample. Show that these date illustrate the law of definite composition.
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