# You have a partially filled party balloon with 2.00 g of helium gas. you then add 2.74 g of hydrogen gas to the balloon. assuming constant temperature and pressure, how many times bigger is the party balloon - comparing before and after the hydrogen gas has been added?

First, we need to get moles of He: moles of He = mass/molar mass of He when the molar mass of He = 4 g/mol                       and when the mass = 2 g    by substitution:   moles of He = 2 g / 4 g/mol                          = 0.5 moles and when V = nRT/P and n is the number of moles so, V1 = 0.5RT/P then, we need moles of H2 = mass / molar mass                                                 = 2.74g / 2g/mol                                                = 1.37 moles ∴ moles of He + moles of H2 = 0.5 moles + 1.37 moles                                                   = 1.87 moles so, V2= 1.87RT/P from the V1 and V2 formula: ∴V2/V1 = 1.87 / 0.5               = 3.74  ∴ the party balloon is 3.74 times bigger

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