a balloon filled with helium has a volume of 30.0L at a pressure of 100mmhgand a temperature of 15.0°C. how many moles of helium does the balloon contain?

Question

a balloon filled with helium has a volume of 30.0L at a pressure of 100mmhgand a temperature of 15.0°C.  how many moles of helium does the balloon contain?

anonymous · Answer

First convert 100mmhg(or Torr) to Kpa (Its easier this way) $$100mmHg \times \frac{ 133.3 Pa }{ 1mmHg}\times \frac{ 1Kpa }{ 1000Pa }=13.32Kpa$$
Then convert degrees to kelvin (you just have too) $$15^{o}+273.15K =288.15K$$
Use the following equation $$pV = nRT$$ Ideal gas equation, where 'p' is pressure, 'V' is volume, 'n' is moles, 'R' is a constant (8.314 in Kpa), 'T' is temperature in kelvins. (note: 'R' constant changes with different pressures).
$$n=\frac{ pV }{ RT }$$solve for 'n' (moles)
$$n=\frac{ 13.32Kpa \times30L }{ 8.314\times288.15 }=1.669molHe$$This is the answer.