Avogadro's Law & Molar Volume (PDF)

Avogadro’s Law AND MOLAR VOLUME 1  Law of Combining Volumes Gay-Lussac also performed experiments to determine the volumes of gases in chemical reactions, in particular that between hydrogen and oxygen He observed that two volumes of hydrogen gas combined with one volume...

Avogadro’s Law AND MOLAR VOLUME 1  Law of Combining Volumes Gay-Lussac also performed experiments to determine the volumes of gases in chemical reactions, in particular that between hydrogen and oxygen He observed that two volumes of hydrogen gas combined with one volume of oxygen gas to form two volumes of water He concluded that when gases react, the volumes of gaseous reactants and products, measured under the same conditions of temperature and pressure, are always whole number ratios. This is now known as the law of combining volumes. However, he could not explain his observations. 2  Avogadro’s Law It took Italian scientist Amadeo Avogadro to explain Gay-Lussac’s observations. In 1811, he proposed that the law of combining volumes could be explained if equal volumes of gases contained the same number of particles. At the time his hypothesis was met with great skepticism and was ignored for over 50 years, but was eventually accepted as more observations supported it. 3  Avogadro’s Law The volume of a gas at a constant temperature and pressure is directly proportional to the number of moles. nαV 4  KMT & Avogadro’s Law When more gas enters a container, the increase in the number of molecules causes the pressure to increase. Because the pressure inside the container is greater than the external pressure at constant temperature, the volume will increase. The volume will continue to increase until the internal pressure caused by the gas becomes equal to the external pressure. 5  Mathematical Expression 𝑛1 𝑛2 = 𝑉1 𝑉2 Where n represents the amount of gas in moles and V represents it’s volume. Remember, the pressure and temperature remain constant. 6 Example #1 At STP, 1.0 mol of carbon dioxide gas has a volume of 22.41 L. What mass of carbon dioxide is present in 3.0 L? 7  Molar Volume (v) 𝑽 𝒗= 𝒏 Condition Pressure Temperature Molar Volume (v) Standard Temperature and 101 kPa 0°C 22.4 L/mol Pressure (STP) Standard Ambient Temperature and Pressure 100 kPa 25°C 24.8 L/mol (SATP) The volume of one mole of any gas is referred to as its molar volume (v), and it is the same for all gases. 8  Relationship Between Moles and Volume Molar volume is a conversion factor that allows you to convert from moles to volume of a gas if the gas is at standard conditions (STP or SATP). 9 Example #2 An experiment generates 0.152 g of hydrogen gas. What volume of gas was generated at STP? 10 Example #3 Find the volume that 20.0 g of carbon monoxide gas occupies at SATP. 11