A NOTHER W AY TO M EASURE G ASES - V OLUME

The volume of a gas can be influenced by both temperature and pressure. Because of this behavior, it is necessary to specify the temperature and pressure whenever the volume of a gas sample is given. Scientists have chosen a "standard" temperature and pressure so that it is easier to relate gas volumes to one another. These "standard" conditions are: standard temperature: 0 o C standard pressure:101.3 kPa OR (1.00 atm) or(760 mm Hg) Note: " STP " is the abbreviation for standard temperature and pressure.

In the early 1800's, John Dalton had been working on a theory of matter and proposed that all matter was made of particles. At the same time, Gay-Lussac had discovered that when two gases combine to form a new substance, they do so in simple volume ratios. e.g. 1 L of oxygen combined with 2 L of hydrogen to give 2 L of gaseous water In 1811, the Italian scientist Amadeo Avogadro published a hypothesis (which was at first ignored) which to this day is called Avogadro's Hypothesis. It states that equal volumes of different gases at the same temperature and pressure contain equal numbers of molecules

Avogadro's Hypothesis can be rearranged to read: equal numbers of molecules at the same temperature and pressure have equal volumes. Experiments have confirmed this prediction, and have lead to the following: At standard temperature and pressure (STP), one mole of any gas has a volume of 22.4 litres. The quantity 22.4 L is known as the molar volume of any gas at STP.

S AMPLE P ROBLEMS : 1.Determine the volume, in litres, of moles of SO 2 gas at STP.

2. Determine the number of moles in 33.6 L of He gas. (Assume STP)

3.How many molecules are there in 15.0 L of hydrogen gas at STP? 4.Calculate the volume of 25.0 g of chlorine gas at STP.

5.The density of a gaseous compound of carbon & oxygen is kg/m 3 at STP. Determine the molar mass of the compound. What is the compound?