Calculate the Pressures of H2 and He: Are answers correct?

  • Thread starter blackjack18
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In summary, the formula for calculating pressures of H2 and He is P = nRT/V, where P is the pressure, n is the number of moles, R is the ideal gas constant, T is the temperature in Kelvin, and V is the volume. The number of moles for H2 and He can be determined by dividing the given mass of each gas by their respective molar masses. The ideal gas constant used in the formula is R = 0.0821 L·atm/mol·K. To convert the temperature from Celsius to Kelvin, you can use the formula K = °C + 273.15. This will give you the temperature in Kelvin, which is necessary for the pressure calculation. To check
  • #1
blackjack18
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A mixture of 1.00 g of H2 and 1.00 g of He is placed in a balloon of volume 1.0 L when filled with these gases at 27 deg C.

A) calculate the partial pressure of each gas and the total pressure

pressure of H2-12.315 atm?
pressure of He-6.158 atm?

B) calculate the mole fraction of He in the mixture.


I need help with B
 
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  • #2
(A) Looks right

(B) Start with how many moles of each gas are present.
 
  • #3


A) To calculate the partial pressure of each gas, we can use the ideal gas law:

PV = nRT

Where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature in Kelvin.

First, we need to calculate the number of moles of each gas present in the mixture:

n(H2) = 1.00 g / (2 g/mol) = 0.50 mol
n(He) = 1.00 g / (4 g/mol) = 0.25 mol

Now, we can plug these values into the ideal gas law to calculate the partial pressures:

P(H2) = (0.50 mol)(0.082 L atm/mol K)(300 K) / 1.0 L = 12.3 atm
P(He) = (0.25 mol)(0.082 L atm/mol K)(300 K) / 1.0 L = 6.2 atm

The total pressure of the mixture is simply the sum of these two partial pressures:

P(total) = 12.3 atm + 6.2 atm = 18.5 atm

B) To calculate the mole fraction of He in the mixture, we can use the following formula:

X(He) = n(He) / n(total)

Where X(He) is the mole fraction of He, n(He) is the number of moles of He, and n(total) is the total number of moles in the mixture.

In this case, n(total) = n(H2) + n(He) = 0.50 mol + 0.25 mol = 0.75 mol

Therefore, the mole fraction of He is:

X(He) = 0.25 mol / 0.75 mol = 0.33

This means that approximately one-third of the moles in the mixture are He.
 

1. What is the formula for calculating pressures of H2 and He?

The formula for calculating pressures of H2 and He is P = nRT/V, where P is the pressure, n is the number of moles, R is the ideal gas constant, T is the temperature in Kelvin, and V is the volume.

2. How do you determine the number of moles for H2 and He?

The number of moles for H2 and He can be determined by dividing the given mass of each gas by their respective molar masses. The molar mass of H2 is 2 g/mol and the molar mass of He is 4 g/mol.

3. What is the ideal gas constant used in the formula for calculating pressures of H2 and He?

The ideal gas constant used in the formula is R = 0.0821 L·atm/mol·K.

4. How do you convert the temperature to Kelvin?

To convert the temperature from Celsius to Kelvin, you can use the formula K = °C + 273.15. This will give you the temperature in Kelvin, which is necessary for the pressure calculation.

5. How can you check if your calculated pressures for H2 and He are correct?

You can use the ideal gas law to calculate the pressure of each gas and compare it to your calculated values. If they are close in value, then your calculations are likely correct. You can also check for any calculation errors and ensure that you are using the correct units for each variable.

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