Since, at a constant pressure, the volume of an ideal gas is directly proportion

Question

Since, at a constant pressure, the volume of an ideal gas is directly proportional to its temperature, the plot of volume versus temperature is a straight line. When temperature is plotted on the Celsius scale, the straight line can be extrapolated to the point where the volume is zero and the temperature is - 273 degree C. Because matter cannot have a negative volume, - 273 degree C must be the lowest possible temperature, absolute zero A cylinder with a movable piston contains 2.00 g of helium, He, at room temperature. More helium was added to the cylinder and the volume was adjusted so that the gas pressure remained the same. How many grams of helium were added to the cylinder if the volume was changed from 2.00 L to 4.50L ? (The temperature was held constant.) Express your answer with the appropriate units mass of helium added =

Explanation / Answer

1) Convert grams of He to moles:

2.00 g / 4.00 g/mol = 0.500 mol

2) Use Avogadro's Law:

V1/n1 = V2/n2

2.00 L / 0.500 mol = 4.50 L / x

x = 1.125 mol

3) Compute grams of He added:

1.125 mol - 0.500 mol = 0.625 mol

0.625 mol x 4.00 g/mol =2.5 grams of He added

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