1. A 20 L cylinder containing helium gas at a pressure of 29.5 atm is used to fi

Question

1. A 20 L cylinder containing helium gas at a pressure of 29.5 atm is used to fill a weather balloon in order to lift equipment into the stratosphere. To what maximum pressure (in atm) could a 155 L balloon be filled.

2. A 27.0 L cylinder containing helium gas at a pressure of 43.0 atm is used to fill a weather balloon in order to lift equipment into the stratosphere. What is the final pressure (in atm) in the cylinder after a 219 L balloon is filled to a pressure of 1.25 atm.

3.The reaction of magnesium metal with HCl yields hydrogen gas and magnesium chloride. What is the volume, in liters, of the gas formed at 760 torr and 21 oC from 6.99 g of Mg in excess HCl? (Hint, first write the balanced equation.)

Explanation / Answer

1. P1V1 = P2V2

So P2 = P1V1/V2 = 20 x 29.5/155 = 3.81atm

2. PiVi = PfVf where i indicates initial and f indicates final

So 27 x 43 = 219 x 1.25 + 27 x P

So P = (27 x 43 - 219 x 1.25)/27 =32.86 atm

3. Mg + HCl = MgCl2 + H2

no. of moles of Mg = 6.99/24 = 0.29

So moles of H2 is 0.29

760 torr = 1 atm, T =294 K

V = nRT/P = 0.29 x 0.0821 x 294/1 = 7 L

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