explore Avogadro’s contribution to the Gas Laws

Avogadro and the Gas Laws In this presentation you will: • explore Avogadro’s contribution to the Gas Laws Next >

Early Discoveries The English scientist Henry Cavendish (1731 to 1810) established that when hydrogen and oxygen combine (to form water), they always combine in the ratio 2:1 atoms. Next >

Early Discoveries This was repeated by others including Joseph-Louis Gay-Lussac. He published in 1808 and noted that, not only was Cavendish correct, but all reactions between gases and the gaseous products produced are in simple ratios of whole numbers. Next >

Avogadro’s Law Amedeo Avogadro (1776–1856) was an Italian scientist. He lived in the northern part of Italy that was then governed by Napoleon. He studied the work of Gay-Lussac and in 1811 published his hypothesis. This is now known as Avogadro’s Law. Next >

Avogadro’s Law Avogadro’s Law states that equal volumes of all gases contain equal numbers of particles, provided they are at the same temperatures and pressures. Next >

Another Way of Stating Avogadro’s Law Avogadro’s Law allowed chemists to compare the relative masses of the molecules in two gases, simply by comparing the masses of equal volumes of the gases. We now need to look at how Avogadro’s Law is applied. Next >

Applying Avogadro’s Law Suppose we have n litersof an unknown gas X. We know, from Avogadro’s Law, that n liters of hydrogen will contain the same number of molecules as our unknown gas, X. If we find the mass of n liters of hydrogen and n liters of X, we should be able to establish a relationship: Mass of n liters of X Mass of n liters of hydrogen Mass of one molecule of XMass of one molecule of hydrogen = Next >

Applying Avogadro’s Law If we now have another gas Y and take n liters of this gas: Mass of n liters of Y Mass of n liters of hydrogen Mass of one molecule of YMass of one molecule of hydrogen = Next >

Comparison to a Standard The masses of molecules X and Y can now be compared since we have compared each of them to the “standard” mass of hydrogen. As long as all chemists agree on the standard, it is possible to compare the masses of any gases. Y X Nowadays, carbon-12 is used as the standard, but the principle is exactly the same. Next >

Standard Temperature and Pressure There is one other standard, that needs to be established. Avogadro’s Law says that the volumes must be measured at the same temperature and pressure. T P 273 K What are the values of this temperature and pressure? 5 1 × 10 Pa These have been agreed as 273 K and 1  105 Pa and are known as standard temperature and pressure (s.t.p.). Next >

Moles and Molar Volume A mole of a substance is defined as 6.022 × 1023 particles of the substance. 6.022 × 1023 is known as Avogadro’s Number. One of the implications of Avogadro’s Law is that a mole of any gas should occupy the same volume at s.t.p. This is known as the molar volume and is 22.4 liters. Next >

Question 1 What is the volume of a gas proportional to according to Avogadro? A) The number of moles of gas present B) The mass of gas present C) The number of molecules present D) All of the above Next >

Question 2 What is standard temperature and pressure? A) 0 °C and 1  105 Pa B) 100 °C and 1  105 Pa C) 273 K and 1  105 Pa D) 273 K and 1  106 Pa Next >

Summary In this presentation you have seen: • Avogadro’s contribution to the Gas Laws End >

explore Avogadro’s contribution to the Gas Laws