Quantative chemistry For each of the laws in

Quantative chemistry • For each of the laws in the following slides, think of where in today’s chemistry we use them. • What is a “law” in science? • Do we know if these laws are always right? • Why do we accept them and work with them? • How do you think they obtained the evidence?

Law of Conservation of Mass Lavoisier - 18 th century From studying reactions involving oxygen, Lavoisier concluded that during any chemical reaction no atoms were destroyed and therefore the mass remains the same during any chemical reaction.

Law of Definite Proportions Joseph-Louis Proust - 1797 • Analytical tests showed that a pure substance consists of the same elements in definite proportions. • Example: water is always 88. 88 % oxygen by mass.

Law of Combining Volumes of Gases Gay-Lussac - 1803 • When gases react, they do so in whole number ratios in terms of volumes. • Example: 3 volumes of hydrogen react with 1 volume of nitrogen to form 2 volumes of ammonia.

Law of Multiple Proportions Dalton - 1800’s In 2 different compounds of the same elements, if the mass of 1 element is the same (e. g. 12 g C in CO and CO 2) than the ratio of the mass of the other element (e. g. 16 g and 32 g for oxygen) in each compound must be whole number.

Avogadro’s Law - 1811 Equal volumes of different gases at the same temperature and pressure must have equal number of particles (this explains Gay. Lussac’s Law).